personal space research paper

ORIGINAL RESEARCH article

Personal space increases during the covid-19 pandemic in response to real and virtual humans.

• 1 The Department of Psychiatry, Massachusetts General Hospital, Boston, MA, United States
• 2 Harvard Medical School, Boston, MA, United States
• 3 The Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States
• 4 The Department of Radiology, Massachusetts General Hospital, Boston, MA, United States

Personal space is the distance that people tend to maintain from others during daily life in a largely unconscious manner. For humans, personal space-related behaviors represent one form of non-verbal social communication, similar to facial expressions and eye contact. Given that the changes in social behavior and experiences that occurred during the COVID-19 pandemic, including “social distancing” and widespread social isolation, may have altered personal space preferences, we investigated this possibility in two independent samples. First, we compared the size of personal space measured before the onset of the pandemic to its size during the pandemic in separate groups of subjects. Personal space size was significantly larger in those assessed during (compared to those assessed before) the onset of the pandemic (all d  > 0.613, all p  < 0.007). In an additional cohort, we measured personal space size, and discomfort in response to intrusions into personal space, longitudinally before and during the pandemic, using both conventional and virtual reality-based techniques. Within these subjects, we found that measurements of personal space size with respect to real versus virtual humans were significantly correlated with one another ( r  = 0.625–0.958) and similar in magnitude. Moreover, the size of personal space, as well as levels of discomfort during personal space intrusions, increased significantly during (compared to before) the COVID-19 pandemic in response to both real and virtual humans (all d  > 0.842, all p  < 0.01). Lastly, we found that the practice of social distancing and perceived (but not actual) risk of being infected with COVID-19 were linked to this personal space enlargement during the pandemic (all p  < 0.038). Taken together, these findings suggest that personal space boundaries expanded during the COVID-19 pandemic independent of actual infection risk level. As the day-to-day effects of the pandemic subside, personal space preferences may provide one index of recovery from the psychological effects of this crisis.

Introduction

Personal space is the “comfort zone” surrounding the body that is typically maintained free of intrusions from others in order to protect the organism from harm ( Hayduk, 1983 ; Graziano and Cooke, 2006 ). The monitoring and defense of this space is an evolutionarily conserved function of the brain across many species, from insects to mammals ( Graziano and Cooke, 2006 ). In humans, the dimensions of personal space are moderately influenced by a number of situational, social, and psychological factors, including gender, age, social status, cultural norms, and psychological characteristics ( Hayduk, 1983 ; Uzzell and Horne, 2006 ; Kennedy and Adolphs, 2014 ; Holt et al., 2015 ; Iachini et al., 2016 ). However, when many of these situational factors are controlled within a laboratory setting, the preferred distance that a given individual maintains from others remains remarkably stable over repeated measurements ( Hayduk, 1981 ; Tootell et al., 2021 ).

Since early 2020, “social distancing” recommendations aiming to reduce transmission of the COVID-19 virus have influenced how far people stand from each other in many public settings. These consciously adopted distances (usually 6 feet in the US, and 2 meters elsewhere) are much larger than those generated by the intrinsic brain mechanisms involved in personal space regulation (e.g., 50–100 cm) ( di Pellegrino and Làdavas, 2015 ). However, it is unclear whether the practice of social distancing, and other effects of the pandemic on social interactions ( Killgore et al., 2020 ; Tull et al., 2020 ; Calbi et al., 2021 ), have broadly influenced personal space regulation. To examine this question, we measured personal space in two independent cohorts of subjects. In addition, in the second cohort, personal space size was measured with respect to both real people and avatars presented using virtual reality technology. With these data, we tested the prediction that the size of personal space, assessed in the laboratory using the well-validated Stop Distance Procedure ( Hayduk, 1983 ; Kaitz et al., 2004 ), increased during the pandemic, even in a virus-free, virtual reality context.

Materials and methods

Participants.

A subset of the participants of a study of the mental health of college students ( Burke et al., 2019 ; DeTore et al., 2022 ) underwent a comprehensive in-person clinical and cognitive assessment that included measurements of personal space size with human confederates (see details below). A total of 249 participants were assessed (65.1% female, mean age: 19.0), including (1) n  = 178 in 2017–2019 (65.2% female; mean age: 19.0), (2) n  = 38 in January and February of 2020, immediately prior to the beginning of the pandemic and the institution of the associated restrictions and mandates in Boston (68.4% female, mean age: 18.7), and (3) n  = 33 after March 2020, during the pandemic (60.6% female, mean age: 19.3). There were no significant differences in age or gender across these three groups (see Supplementary Table S1 for additional demographic information about this cohort). The three groups were 100% independent of each other (with no common subjects). Also, the experimental procedures were identical across these groups, other than some additional precautions implemented during the pandemic (see below).

A second cohort of healthy individuals ( n  = 19, 47% female, mean age: 30.6 ± 11.3 years) were recruited via online advertisement posted on the Massachusetts General Hospital (MGH) Rally Website 1 and initially assessed before the COVID-19 pandemic lockdown began in Boston, MA (during the period between September 2019 and early March 2020; the pandemic lockdown in Boston began on March 13, 2020). A subset of this same group of subjects ( n  = 12, 42% female, mean age: 33.3 ± 11.2 years) returned to complete a second assessment session, which was identical to the first (other than the addition of pandemic-related precautions, see below), during the initial surge of the COVID-19 pandemic in Boston (July–December 2020; see Supplementary Table S2 for additional demographic information about this cohort). All subjects of the baseline sample who were willing and able to return were enrolled in the second session. The two sessions were an average of 10.04 ± 1.6 months apart. Intrinsic personal space preferences have been shown to be stable and measured reliably over that length of time ( Hayduk, 1983 ).

All research protocols were approved by the Mass General Brigham Healthcare Institutional Review Board. Written informed consent was obtained from all subjects prior to enrollment.

Overview of procedures

Throughout this study, we used a well-validated, highly reliable (kappa ~0.8) experimental procedure for measuring personal space size, the Stop Distance Procedure (SDP) ( Hayduk, 1983 ; Kaitz et al., 2004 ). The SDP measures the distance from a subject at which the subject first becomes uncomfortable when another person (the experimental confederate) approaches them (passive trials), or when the subject approaches another person (active trials). Both types of trials measure the distance between the subject’s body and their personal space boundary.

To control additional variables that could potentially influence personal space size (such as varying physical characteristics of the SDP confederates), in Cohort 2 we also collected personal space measurements using an immersive virtual reality (VR) version of the SDP, in addition to the conventional SDP. This VR procedure measures personal space in response to virtual simulations of humans (“avatars”) but is otherwise identical to the SDP conducted with real humans. VR-based measurements of personal space with respect to avatars have been shown to correspond closely to those measured to real humans in vivo ( Iachini et al., 2016 ; Tootell et al., 2021 ).

In addition, in Cohort 2, arousal responses to personal space intrusions (as reflected by subjective discomfort ratings) were measured at different distances within (as well as outside of) personal space boundaries, to both real and virtual humans (see details below).

The conventional SDP

Passive SDP trials: Subjects were first asked to stand still while facing a human confederate (a laboratory staff member) who was standing 3 meters away from the subject. Subjects were instructed to maintain eye contact with the confederate, who maintained a neutral facial expression, and told that the confederate would start walking slowly toward them, and that they should say “okay” when the confederate reached the distance that the subject would typically maintain from a person they had just met. For these passive trials, the confederates were trained to walk at approximately 0.1 m/s. Passive SDP trials were collected in both Cohorts 1 and 2.

Active SDP trials: In Cohort 2, the active version of the SDP was also conducted, in addition to the passive version. Active trials began similarly to the passive trials, with the subject standing 3 meters away from the confederate. However, in the active version of the procedure, the subjects were instructed to approach the confederate, and to stop at the distance described above and say “okay.” Again, subjects were asked to maintain eye contact with the confederate, who maintained a neutral facial expression.

Both the active and passive SDP trials were conducted with a male and a female confederate, in a counterbalanced order, with two trials per gender.

The VR-based SDP

A HTC VIVE Virtual Reality System was used to collect the VR-based SDP and the measurements of responses to personal space intrusions by avatars. A head-mounted display (HMD) presented stereoscopic images at a resolution of 1,080 × 1,200 pixels per eye, with a 110° field of view at a refresh rate of 90 Hz. A software program for measuring personal space (designed by the research team and developed by Productive Edge, 2 Chicago, Illinois, United States) was run via a SteamVR platform on an Alienware 15 R3 Laptop. In the HMD, each avatar was presented in the identical simple environment (a room with white walls, see Supplementary Figure S1 ). The avatars (i.e., non-player characters) could be placed at different distances from the subjects and could appear to walk toward subjects while maintaining eye contact with them. Both active and passive SDP trials were conducted using four different avatars (two males and two females, 50% non-white in appearance). The SDP type (active or passive), SDP modality (real or virtual), and confederate order were counterbalanced across subjects. There were two trials per avatar, with a total of eight active trials and eight passive trials (16 trials per time point).

In the VR environment, the height of each avatar was set to equal the height of the subject, and the approach speed was set at 0.1 m/s. As with the conventional SDP, in the passive trials, subjects were asked to stand still and maintain eye contact with an avatar that began walking toward them. The subjects were instructed to say “okay” when the avatar reached the distance that they would typically maintain from such a person they had just met. During the active trials, the subjects were instructed to approach the avatar, and to stop at this distance and at the same time say “okay.”

Summary of design and number of trials of the SDP

Thus, for Cohort 1, the SDP included only passive trials with human confederates (the standard procedure), with a total of 4 trials collected per subject (two trials per each confederate gender).

In Cohort 2, the SDP included both passive and active trials (with two trials per each confederate gender), with both human (1 male and 1 female: 4 trials × 2 (passive and active) = 8 trials) and avatar (2 male and 2 female: 8 trials × 2 (passive and active) = 16 trials) confederates (a total of 24 SDP trials), at two time points (before and during the pandemic). Thus for Cohort 2, a total of 48 SDP trials were collected per subject.

Responses to personal space intrusions

In Cohort 2, discomfort in response to personal space intrusions was also measured, in addition to personal space size. First, personal space size was calculated independently in each individual subject for each of the two SDP modalities (real and virtual), using the average personal space size measured in the active trials of that visit, which are slightly more stable than the passive trials ( Tootell et al., 2021 ). Then multiples of each individual subject’s personal space size (25, 50, 100, 200, and 400%) were calculated. To measure discomfort in response to personal space intrusions, real or virtual humans were presented in separate runs at these 5 distances from the subject in a counterbalanced, pseudorandomized order. For each trial, the subject began the trial with their eyes closed, and then was asked to open their eyes during the presentation of each stimulus. The subject was instructed to stand still during the stimulus presentation and maintain eye contact with the real or virtual human. During each presentation, subjects were asked to rate their agreement to the statement “I want to move away” (indicating subjective discomfort) on a Likert scale from 1–5 (1: not at all, 3: somewhat, 5: very much). The order of modality (i.e., of the two procedures conducted with real vs. virtual humans) was the same as the order used for the initial SDP measurement within each subject and visit ( Tootell et al., 2021 ).

Fitting power law functions

A prior study demonstrated that relative magnitudes of discomfort in response to varying personal space intrusions (as above) were best approximated by a power law function ( Tootell et al., 2021 ). To test whether such a pattern of discomfort responses was altered during the pandemic in Cohort 2, power law functions as D = a x b were fitted to the pooled discomfort ratings for each time point, where D is the reported discomfort level, x is the distance between the subject and the real or virtual human (as a percentage of pre-pandemic personal space size), and a , b (the prefactor and the exponent, respectively) are parameters obtained by minimizing the sum squared error between the power law function and the data. Separate power law functions were fitted to the data collected before and during the pandemic, and for the procedures using real and virtual humans. To test whether the power law functions were significantly different before versus during the pandemic, the fitting procedure was repeated 1,000 times in each case, by bootstrapping the data with substitution. The resultant a and b parameters of the two time points (before and during the pandemic) were compared using the nonparametric two-sample Kolmogorov–Smirnov (KS) test, separately for real and virtual humans.

COVID-19 safety procedures

For assessments occurring during the pandemic, subjects were screened for COVID-19 symptoms and travel within 48 h of arrival in accordance with MGH guidelines. In addition, mask-wearing and social distancing policies were in effect for all subjects and staff members throughout the majority of the research visits. The only exception to this (approved by the MGH COVID safety team) was during the SDP measurement of personal space to real humans; in this case, the subject wore a mask and protective eye goggles, while the confederate (i.e., staff member) did not wear a mask. This was done in order to maintain the same SDP conditions from the perspective of the subject (facing someone who is not wearing a mask) before and during the pandemic. Immediately following the SDP procedure, the staff member resumed wearing a mask.

Statistical analyses

A one-way ANOVA was used to test for differences among the three groups in the size of personal space, and significant effects were followed up by Independent Sample t -tests, to test the hypothesis that personal space was larger during, compared to before, the pandemic.

Repeated-measure ANOVAs (modality × time) and paired samples t -tests were used to test for differences in personal space size and discomfort ratings across modality (real and virtual) and the two time points (before and during the pandemic), to test the hypothesis that personal space size and discomfort in response to personal space intrusions increased during vs. before the pandemic in this cohort. Significance values (for paired t -tests comparing discomfort ratings across distances) were corrected for multiple comparisons (alpha = 0.05, Bonferroni corrected), within each time point and modality. Change scores were calculated as the difference between values collected at the second and first time point (i.e., “During” minus “Before” the COVID-19 pandemic). Thus, a positive change score indicated an increase in the respective measure over time.

Correlations

Because some of the Cohort 2 personal space measurements and the self-report questionnaire data were not normally distributed, Spearman’s correlations were used in the correlation analyses, including those measuring relationships between (1) personal space size during the pandemic and (2) changes in personal space size over time and:

1. local rates of COVID-19 cases, measured as the positive COVID-19 case rate during the previous 2 weeks in the town in which the subject lived (obtained from Massachusetts Department of Public Health COVID-19 data archive). 3

2. self-reported beliefs and experiences related to the pandemic ( Gerhold, 2020 ), including the perceived risk of COVID infection and the practice of social distancing.

Correlations with symptoms of psychopathology and distress were also explored, including anxiety and distress related to the pandemic, as well as levels of depression ( Beck et al., 1961 ), anxiety ( Spielberger et al., 1983 ), and subclinical psychotic symptoms ( Peters et al., 1999 ; Supplementary Table S1 ).

A one-way ANOVA [ F (246,248) = 5.698, p  = 0.004] revealed that in Cohort 1, the size of personal space (measured with respect to real humans) was significantly larger in the group assessed during the pandemic compared to both: (1) those assessed in early 2020 [ t (69) = −3.076, p  = 0.003] and (2) those assessed more than 6 months before the pandemic [ t (209) = −3.238, p  < 0.001; Figure 1 ].

Figure 1 . The size of personal space was larger during (compared to before) the pandemic (Cohort 1). Bar plots of mean personal space size, as measured by the standard Stop Distance Procedure (using human confederates), of the three groups of subjects in Cohort 1 are shown. Personal space size was significantly larger in the group assessed during the pandemic (light blue bar) compared to (1) those who had been assessed in early 2020 [1 month before the pandemic; t (69) = −3.076, p  = 0.003; right dark blue bar] and (2) those who had been assessed well before the pandemic [> 6 months before the pandemic; t (209) = −3.238, p  = 0.001; left dark blue bar]. There was no significant difference between the mean personal space size of the two groups assessed before the pandemic [ t (214) = −0.222, p  = 0.824]. Error bars indicate standard errors of the mean. * p  < 0.005.

As expected ( Tootell et al., 2021 ), in Cohort 2, the size of personal space with respect to real humans was highly correlated with the size of personal space to virtual humans (avatars) across individuals, for both the passive and active trials, both before [passive trials: r (17) = 0.625, p  = 0.004; active trials: r (17) = 0.644, p  = 0.003] and during [passive trials: r (10) = 0.958, p  < 0.001; active trials: r (10) = 0.790, p  = 0.002] the COVID-19 pandemic.

In addition, within these Cohort 2 subjects, the size of personal space was significantly larger during, compared to before, the COVID-19 pandemic for all four measurements of personal space size [real humans: passive trials: t (11) = 5.732, d  = 1.655, p  < 0.001; active trials: t (11) = 3.863, d  = 1.115, p  = 0.003; virtual humans: passive trials: t (11) = 2.918, d  = 0.842, p  = 0.014; active trials: t (11) = 3.082, d  = 0.890, p  = 0.01; see Table 1 ; Figure 2 ; Supplementary Table S3 ]. Also, these changes in personal space size during the pandemic to real and virtual humans were significantly correlated with each other (passive trials: r  = 0.608, p  = 0.036; active trials: r  = 0.762, p  = 0.004; See Supplementary Figure S2 ).

Table 1 . Personal space size measurements, Cohort 2.

Figure 2 . Personal space size and discomfort during personal space intrusions increased longitudinally within individuals during the COVID-19 pandemic (Cohort 2). (A) Examples of real and virtual human confederates that were used in the Stop Distance Procedure (SDP) and (B) the measurements of mean personal space size in Cohort 2 are shown. Personal space size, measured using the SDP with real and virtual humans, increased significantly during the COVID-19 pandemic within individuals. Also, the increases in personal space during the pandemic to the real and virtual humans correlated with each other (all r  > .608; all p  < .036). (C) Power law fits to the before- and during-pandemic discomfort ratings, as a function of distance from real or virtual humans, expressed as percentages of before-pandemic personal space size, are shown.

Prior work has shown that intrusions into personal space by unfamiliar others lead to an increase in discomfort at progressively closer distances ( Felipe and Sommer, 1966 ; Hayduk, 1981 ; Llobera et al., 2010 ; Schoretsanitis et al., 2016 ), perhaps following a power law function ( Tootell et al., 2021 ). To test whether such personal space intrusion-driven discomfort levels changed during the pandemic, subjects were asked to rate their discomfort in response to real and virtual humans, which were presented at a range of distances (25, 50, 100, 200, 400% of each subject’s personal space size, see “Materials and methods”), both before and during the pandemic.

The discomfort levels as a function of distance followed a power law fall-off, as previously ( Tootell et al., 2021 ) in all four cases (to real humans, before and during the pandemic, respectively: R 2 = 0.71 and 0.67 ; to virtual humans, before and during the pandemic respectively, R 2 = 0.73 and 0.74 ). During the pandemic, discomfort to personal space intrusions increased significantly compared to the pre-pandemic discomfort ratings in response to both real and virtual humans, following a power law (real humans: p  < 0.0001, KS statistic 0.53; virtual humans: p  < 0.0001; KS statistic 0.21; Figure 2C ). Specifically, the prefactor a was significantly different between the two timepoints ( p  < 0.0001 for both real and virtual humans, KS statistics 0.36 and 0.20, respectively) and the exponent b was significantly different between the two timepoints ( p  < 0.0001 for both real and virtual humans, KS statistics 0.53 and 0.21, respectively).

Correlations with beliefs and experiences during the pandemic

For those assessed during the pandemic (of Cohorts 1 and 2 combined, n  = 43), personal space size (in response to real humans, passive trials) was significantly positively correlated with social distancing behavior (ratings of “I stay at least 6 feet away from people when I am outside”; r (41) = 0.358, p  = 0.019; Figure 3A ). There were no significant correlations between personal space size during the pandemic and perceived or actual risk of infection, COVID-related anxiety or distress or any psychopathology measure (all p  > 0.126).

Figure 3 . Associations with social distancing behavior and perceived risk of being infected with COVID-19 during the pandemic. (A) There was a significant correlation between personal space size during the pandemic and social distancing behavior (as assessed using ratings of the statement “I stay at least 6 feet away from people when I am outside”; r (41) = 0.358, p  = 0.019) in the subjects assessed during the pandemic (31 subjects of Cohort 1 and 12 subjects of Cohort 2; total n  = 43). Two subjects of Cohort 1 did not complete the scale measuring beliefs and experiences related to the pandemic. (B) Across all four personal space measurements (i.e., real and virtual, passive and active SDP trials), the change in personal space size observed in Cohort 2 that occurred following the onset of the pandemic (During – Before) was significantly positively correlated with perceived risk of COVID-19 infection (Real: passive: r (10) = 0.745, p  = 0.005, active: r (10) = 0.656, p  = 0.021; Virtual: passive: r (10) = 0.603, p  = 0.038, active: r (10) = 0.738, p  = 0.006).

In Cohort 2, the within-subject increase in personal space size during the pandemic in response to both real and virtual humans was significantly correlated with the perceived risk of being infected with the COVID-19 virus (ratings of “How likely do you think it is that you might become infected with COVID-19 in the near future?”) across all four personal space measurements (all r  > 0.603; all p  < 0.038; Figure 3B ). In contrast, there were no correlations between the increase in personal space size during the pandemic and rates of actual infection, as reflected by case rates in the towns where the subjects lived. Perceived and actual risks of COVID infection were not correlated with each other ( r  = −0.030, p  = 0.927).

Also, ratings of pandemic-related anxiety and distress and social distancing behaviors during the pandemic did not correlate with the increase in personal space size during the pandemic (all p  > 0.073).

Summary of findings

Here we report evidence derived from two independent cohorts of subjects that personal space boundaries expanded during the COVID-19 pandemic. In the first cohort, an increase in personal space size was observed in individuals assessed during the pandemic in comparison to two similar groups assessed either immediately before, or greater than 6 months before, the beginning of the pandemic. In a second smaller cohort, comprehensive measurements of personal space characteristics, collected both before and during the pandemic in the same subjects, revealed a large (~40–50%) increase in personal space size following the onset of the pandemic, accompanied by an increase in discomfort with the physical proximity of others. These longitudinal changes in personal space size occurred in response to both real humans and to avatars encountered in a virtual setting in the absence of COVID infection risk. The fact that the identical effect was observed in response to both real humans and avatars suggests that changes in personal space regulation during the pandemic became somewhat habitual and automatic over time.

Consistent with this interpretation, we also found that the size of personal space during the pandemic was significantly correlated with social distancing. Prior evidence for plasticity in the intrinsic mechanisms involved in monitoring external space near the body ( Canzoneri et al., 2013 ; Martel et al., 2016 ; Serino, 2019 ) suggests that such plasticity occurring in response to social distancing or isolation may underlie changes in personal space-related behaviors during the pandemic. Thus, the current data raise the possibility that experience-dependent modifications in personal space regulation can be maintained and reinforced over time by a habitual behavior such as social distancing. However, further testing of this hypothesis is necessary to fully understand the mechanisms underlying these behavioral changes.

In addition, the perceived, but not the actual, risk of being infected with COVID-19 was correlated with the pandemic-associated change in personal space size in the second cohort. Thus, beliefs about the infectiousness of the virus may have contributed to a preference for greater distance from others during the pandemic, which was manifested even in response to avatars encountered in an immersive virtual reality environment in this study. This link between personal space size and perceived risk of infection replicates and extends a prior finding of an association between self-reported personal space preferences (assessed using a projective, online scale) and perceived, but not actual, COVID-19 infection risk during the early pandemic ( Iachini et al., 2021 ). It is also consistent with a finding of an association between greater segregation of near and far space during the pandemic and greater germ aversion ( Serino et al., 2021 ).

Intriguingly, interpersonal distances measured during the pandemic have been found to be smaller if the confederate in projective measurements of such distances appears to be wearing a mask when compared to non-mask-wearing confederates ( Cartaud et al., 2018 ; Lisi et al., 2021 ; Biggio et al., 2022 ). These findings suggest that the presence of a mask elicits a sense of safety that influences personal space regulation. Based on these findings, we can speculate that the inclusion of mask-wearing confederates in the current study might have reduced or eliminated the pandemic-linked increases in personal space size. However, given that we found that perceived risk of COVID infection was not correlated with actual risk, and perceived infection risk was associated with increases in personal space size during the pandemic, it is possible that the presence of masks (and knowledge about their protective effects) would not have strongly impacted these results.

Subjective discomfort ratings increased in concert with the observed increases in personal space size in the current study. These findings are broadly consistent with other evidence for discomfort with the physical proximity of others during the pandemic, such as higher arousal ratings and more negative appraisals of images depicting large social gatherings during the early pandemic ( Massaccesi et al., 2021 ). The time course of this discomfort response (i.e., the length of time it may take to abate after the most threatening aspects of the pandemic, related to the risks for serious illness, death, or loss, have substantially lessened) remains unclear.

The functions of personal space

Although one goal of maintaining a safety zone around the body is the avoidance of harm ( Graziano and Cooke, 2006 ), in humans there are clearly other functions of personal space-related behaviors beyond the physical protection of the body. Adjustments in personal space during social interactions are used by humans to communicate non-verbal, social signals ( Hayduk, 1983 ) similar to the way that other forms of “body language” convey this type of information to others. For example, smaller interpersonal distances can signal trust, support, or comfort, whereas larger distances can convey fear or respect. During the pandemic, this normally automatic channel of social information exchange has not been fully available in many circumstances, i.e., it has been blunted or modified in many contexts due to social distancing practices, concerns about infection risk, and related avoidance behaviors. The specific impediment to social communication associated with the blunting of “natural” personal space regulation during the pandemic is analogous to that associated with wearing masks (i.e., mask-related interference with facial affect recognition; Pavlova and Sokolov, 2022 ). Given the length of time that such practices were in effect (and are still intermittently reinstated or voluntarily adopted) in some parts of the world, it is not surprising that this specific form of nonverbal communication may have been impacted. Some individuals may require time to regain full use of some of these tools of social interaction, such as personal space regulation.

In addition, individuals who had experienced some impairments in these domains or who had not yet fully developed these skills (e.g., children) before the pandemic may find this period of recovery (or transition to an endemic phase of the pandemic) particularly challenging. Personal space abnormalities have been observed in autism ( Kennedy and Adolphs, 2014 ; Asada et al., 2016 ), schizophrenia ( Park et al., 2009 ; Holt et al., 2015 ; Schoretsanitis et al., 2016 ; Lee et al., 2021 ; Zapetis et al., 2022 ), and Post Traumatic Stress Disorder ( Bogović et al., 2016 ) and have been linked to loneliness ( Layden et al., 2018 ), anxiety ( Iachini et al., 2015 ) and social functioning impairments ( Nechamkin et al., 2003 ; Holt et al., 2015 ; Zapetis et al., 2022 ). Thus, persistently impaired regulation of personal space in certain individuals could indicate a need for further evaluation, close monitoring or therapeutic intervention.

The neural basis of changes in personal space during the pandemic

Although personal space-related behaviors have been linked to the function of the network of parietal and frontal cortical brain regions involved in monitoring the space near the body ( Graziano and Cooke, 2006 ; Huang et al., 2012 ; Cléry et al., 2015 ; di Pellegrino and Làdavas, 2015 ), it is not known whether the function or structure of this network has been altered in parallel with changes in personal space-related behaviors during the pandemic. Given that the functional connectivity of this network ( Holt et al., 2014 ; Zapetis et al., 2022 ) and variability in its responses ( Ferri et al., 2015 ) have been linked to individual differences in personal space preferences, it is possible that changes in this circuit may have accompanied habitual enlargements in personal space during the pandemic. If such changes are persistent, longitudinal neuroimaging studies may be able to detect them and potentially shed light on some of the mechanisms underlying the plasticity of personal space regulation.

Limitations and future directions

The findings of this study must be interpreted with caution due to several limitations of this work. The sample size of the second cohort was small, and inclusion in the second assessment of this cohort was based on the subjects’ willingness and ability to participate in research during the pandemic. However, the effect sizes of the longitudinal changes observed in this cohort were consistently large across all four measurements of the size of personal space (0.84 to 1.66), suggesting that these findings are relatively robust. Follow-up studies will be necessary to determine the time course of these changes as society emerges from the pandemic and resumes social activity levels that are closer to pre-pandemic norms. For those with persistent fears about the risks associated with physical proximity to others, the development of behavioral interventions that address these concerns may be helpful.

Data availability statement

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found at: https://osf.io/hp2n4/?view_only=a017443177bf425087daccd1ca86fd74 .

Ethics statement

The studies involving human participants were reviewed and approved by Massachusetts General Brigham Institutional Review Board. The participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

Author contributions

DH developed the study concept, obtained the funding for the project, and oversaw the study. DH, SZ, and RT were involved in the study design. SZ and JZ collected the data. SZ, JZ, and BB analyzed the data. DH and SZ drafted the manuscript. RT, BB, and JZ revised the manuscript. All authors contributed to the article and approved the submitted version.

This work was supported by the Research Scholar Program of the Executive Committee on Research of Massachusetts General Hospital (DH), and the National Institute of Mental Health (5R01MH109562; DH), and the MGH Translational Neuroscience Training for Clinicians Program (T32MH112485; BB).

Acknowledgments

The authors have no disclosures to report. A preprint of a portion of these results is available on medRxiv ( Holt et al., 2021 ; https://www.medrxiv.org/content/10.1101/2021.06.09.21258234v1 ).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fpsyg.2022.952998/full#supplementary-material

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Keywords: personal space, social distancing, COVID-19, virtual reality, public health, anxiety

Citation: Holt DJ, Zapetis SL, Babadi B, Zimmerman J and Tootell RBH (2022) Personal space increases during the COVID-19 pandemic in response to real and virtual humans. Front. Psychol . 13:952998. doi: 10.3389/fpsyg.2022.952998

Received: 25 May 2022; Accepted: 01 August 2022; Published: 14 September 2022.

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Copyright © 2022 Holt, Zapetis, Babadi, Zimmerman and Tootell. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Daphne J. Holt, [email protected]

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• Published: 25 October 2021

Psychological and physiological evidence for an initial ‘Rough Sketch’ calculation of personal space

• Roger B. H. Tootell 2 , 3 , 4 ,
• Sarah L. Zapetis 1 ,
• Baktash Babadi 1 , 2 ,
• Zahra Nasiriavanaki 1 , 2 ,
• Dylan E. Hughes 1 ,
• Kim Mueser 5 ,
• Michael Otto 6 ,
• Ed Pace-Schott 1 , 2 &
• Daphne J. Holt 1 , 2  

Scientific Reports volume  11 , Article number:  20960 ( 2021 ) Cite this article

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• Neuroscience

Personal space has been defined as “the area individuals maintain around themselves into which others cannot intrude without arousing discomfort”. However, the precise relationship between discomfort (or arousal) responses as a function of distance from an observer remains incompletely understood. Also the mechanisms involved in recognizing conspecifics and distinguishing them from other objects within personal space have not been identified. Accordingly, here we measured personal space preferences in response to real humans and human-like avatars (in virtual reality), using well-validated “stop distance” procedures. Based on threshold measurements of personal space, we examined within-subject variations in discomfort-related responses across multiple distances (spanning inside and outside each individual’s personal space boundary), as reflected by psychological (ratings) and physiological (skin conductance) responses to both humans and avatars. We found that the discomfort-by-distance functions for both humans and avatars were closely fit by a power law. These results suggest that the brain computation of visually-defined personal space begins with a ‘rough sketch’ stage, which generates responses to a broad range of human-like stimuli, in addition to humans. Analogous processing mechanisms may underlie other brain functions which respond similarly to both real and simulated human body parts.

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Introduction.

The widespread recent practice of social distancing during the COVID-19 pandemic has greatly influenced the way we position ourselves relative to others. This social distancing has generated renewed interest in interpersonal space regulation 1 , 2 . Historically, the study of personal space is often traced to ethological observations in the middle twentieth century 3 , 4 , 5 , related to the ‘fight or flight’ interactions between different animals, including predator and prey species. Subsequent studies clarified that the more specific behavior of personal space regulation occurs between members of the same species, i.e. conspecifics 6 , 7 , 8 , 9 . Typically, personal space has been studied in humans, but analogous behavioral interactions have been reported between macaque monkeys 10 .

In studies conducted in humans, personal space has been defined as ‘the area individuals maintain around themselves into which others cannot intrude without arousing discomfort’ 11 , 12 . Often in real life, and in laboratory studies of personal space, a subject positions themself at a consistent distance from an unfamiliar person. The size of personal space or interpersonal distance can vary widely across individuals, often averaging between 60 to 100 cm 11 . Reviews of the literature have concluded that personal space is influenced by age, physical and psychological variables, psychological disorders 13 , 14 , 15 , gender 16 , 17 , 18 , 19 , 20 , and cultural differences. Nevertheless, an individual’s preferred personal space size tends towards a relatively stable default value (a “trait-like” preference), which may be further influenced by these modulating factors.

Several models of the shape of personal space (as defined by discomfort in response to the proximity of others) are illustrated in Fig.  1 . Early models of personal space included a snail shell 21 , or a ‘soap bubble’ 22 , 23 . Those models implied a discrete boundary around the subject, beyond which the level of discomfort due to the presence of another person changes dramatically , e.g. as a step function in the discomfort-by-distance relationship (Fig.  1 a). Subsequently, proposed models were more graded, including an electromagnetic gradient or a compressible spring 24 (e.g. Fig.  1 b–e). However, the exact form of the personal space gradient has remained difficult to define. Hayduk 24 suggested that a combination of linear and nonlinear factors determine personal space (Fig.  1 d). Other studies proposed that the function of distance-by-discomfort is U- or V-shaped 25 , 26 , as elaborated in the social equilibrium model (Fig.  1 e) 19 , 27 , 28 . Another study concluded that the relationship between personal space and absolute distance is ‘curvilinear’ 29 . Adding to the inherent challenges in defining this function are the methodological differences among studies, and the limited number of data points used to estimate the shape of the function in several experiments.

Models of personal space. Qualitative models of variations in discomfort (on the y axis) to an unfamiliar human positioned at different distances from a subject, as a percentage of the subjects’ personal space size (x axis). The dashed vertical line represents the personal space boundary, i.e. 100% of the average SDP value for each subject. The models include a: ( a ) bubble model, ( b ) linear gradient model, ( c ) linear gradient with a threshold, ( d ) power law, and ( e ) social equilibrium model. The panels also show the hypothesized changes in discomfort for each model, as variations in red shading (most discomfort = most saturated red).

Based on this literature, the primary goal of the current study was to clarify the ‘distance-by-discomfort’ function of personal space processing, in ways that are complementary to prior experiments, in several respects. First, prior studies have typically investigated personal space across subjects based on absolute physical distance. Here we instead measured responses to distances from the subject after normalization to the threshold personal space measurement in each given individual. As an analogy, heights across human individuals have a certain variability when based on absolute distance—but the variability decreases significantly when height is normalized by the size of other body parts, e.g. arm length 30 , 31 , 32 .

Second, we measured the discomfort-by-(normalized)-distance functions within a given individual using both (1) discomfort ratings and (2) measurements of ‘arousal’, based on palmar skin conductance responses (SCR). Such dual measurements within each subject made it possible to test the degree to which self-reported discomfort ratings corresponded to visceral discomfort at correspondingly closer interpersonal distances. More broadly, the dual measurements allowed us to test whether psychological ratings and physiological measurements yielded similar or disparate functions.

Third, these measurements were collected during intrusions into personal space of both humans and human-like avatars. By comparing responses to real and virtual humans, we tested a neural model in which the brain calculates personal space in multiple stages. In this model, the brain first calculates a default ‘rough sketch’ of nearby objects and their spatial arrangement relative to the observer, along with ‘tags’ for objects that may be socially or personally relevant. Neurobiological evidence suggests that this stage might be linked with the re-encoding of surrounding space from eye-centered to body- (or person-) centered space, which may involve posterior parietal cortex 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 . Subsequent stages involving higher level cortical areas presumably fine-tune decisions about whether a given intruder is in fact human, and account for more subtle modulating factors (e.g. age, culture, gender, psychological characteristics), and then mediate motor and visceral responses to intruders.

Crucially here, the human-like avatars were instantly and unambiguously distinguishable from real humans. Our rough sketch hypothesis predicted that the expected effects of personal space intrusion (e.g. increased subjective discomfort and increased physiological responses at distances that are at or within the individual’s personal space boundary) would be evoked similarly in response to both humans and avatars.

Nineteen healthy subjects were included in the main experiment (9 female, mean age = 30.6 ± 11.3 years). Data collected in a previously assessed cohort of 30 healthy subjects (8 female, mean age = 26.1 ± 6.1) were also examined to further validate the reliability and stability of the conventional procedures we used to measure the size of personal space in humans. Subjects from both cohorts were recruited via online advertisement posted on the Massachusetts General Hospital Rally Website. Participants were required to be 18–55 years old and without an unstable medical or neurologic illness or diagnosis of a psychiatric disorder 41 , and have normal (or corrected to normal) vision. All experimental protocols were approved by, and all procedures were performed in accordance with the guidelines and regulation of the Mass General Brigham Healthcare Institutional Review Board. Written informed consent was obtained from all subjects prior to enrollment.

The 19 subjects enrolled in the main experiment were also screened for virtual reality (VR) sickness (vertigo or nausea) using the Simulator Sickness Questionnaire 42 after spending ~ 10 min in the immersive VR system. No subjects were excluded due to VR sickness. Based on prior work showing that physical characteristics such as arm length may influence personal space size 32 , arm length (from the shoulder to the fingertips) and arm span (fingertips on one hand to those on the other, with horizontally oriented arms) were measured in each subject.

All data were collected prior to March 9, 2020, i.e. before the initial surge of the COVID-19 pandemic in the Boston area when the resulting infection control mandates, including social distancing recommendations, were adopted. Thus, subjects in these experiments did not wear face masks, and had no experience with mandated social distancing.

Personal space measurement

Personal space size was measured using the well-validated Stop Distance Procedure (SDP) 11 , 43 . Two types of SDP measurements were collected, using a ‘passive’ 44 and an ‘active’ procedure 45 . In addition, each procedure was repeated in two different modalities: in real physical space with human intruders, and in an immersive virtual reality (VR) environment using human-like avatars. (Here we use the term ‘intruder’ to refer to the study staff member who positioned themselves at different distances from the subject or the analogous virtual character in the VR environment).

In the ‘passive’ measurements, subjects were asked to stand still, facing the intruder, who initially stood 3 m from the subject. Subjects were instructed as follows: “ Please stand still as my colleague walks slowly towards you. Say ‘okay’ when they reach a distance at which you would normally stand to talk to someone who you have just met. When you say ‘okay’, they will pause… Please make sure to maintain eye contact with my colleague throughout the procedure ”. The intruder maintained a neutral facial expression throughout the measurements. The distance between the subject and the intruder (the ‘stop distance’) was measured by a staff member after each trial, defined as the distance between the proximal tips of their shoes on the floor. The stop distances were considered to represent the preferred size of personal space for each subject.

The ‘active’ measurements began similarly, with the subject and intruder standing 3 m apart. In this procedure, the instructions were: “ Please walk up to my colleague and stop at the distance at which you would normally stand to talk with someone who you have just met. Please make sure to maintain eye contact with them throughout the procedure ”. Again, the subject was instructed to stop and say ‘okay’ at the final chosen distance. This stop distance was measured and recorded by a staff member.

These experiments measured responses to both real humans and to human-like avatars (Fig.  2 ; Informed consent was obtained from the two individuals shown in Fig.  2 a to publish these images in an online open-access publication). The VR-based SDP procedures and instructions were generally the same as those described above, except that an avatar (who was controlled by a member of the study staff) was presented instead of a human, within an immersive environment (a generic virtual room).

Examples of human and virtual ‘intruders’. The examples shown here include real humans (left and middle right rows, a male and female, respectively) and avatars (middle left and right rows) which served as ‘intruders’ in the Stop Distance Procedures and the Distance Range Experiments. Human and virtual intruders were positioned at systematically varied distances. The distance variations were based on a percentage of each subject’s personal space size. For this illustration, the personal space size was arbitrarily set at 75 cm. The avatars displayed here are highly similar in appearance to the human subjects shown, in order to illustrate minimum possible differences in appearance between the humans and avatars that could be achieved. Despite the similarities of these examples, it is easy to distinguish the avatars from the human subjects. In the actual experiment, the humans and avatars viewed by each participant were not necessarily similar in appearance. Also, additional cues made it trivial to distinguish the real versus virtual intruders (e.g., subjects were clearly aware of whether they were wearing VR goggles, or not).

In the procedures using human intruders, we presented one male and one female to each subject (both of whom were previously unknown to the subject). In the procedures using avatars, there were four different intruders (two male and two female avatars). For each subject, each type of measurement (active and passive) of the SDP was repeated twice for each human or avatar intruder, resulting in 4 trials with humans and 8 trials with avatars per SDP type. In the VR environment, the height of each avatar was set to the height of the subject, and the approach speed was set at 0.1 m/sec. In the version using humans, the human intruders were trained to walk at approximately the same speed as the avatars. Across subjects, the following were counterbalanced: (1) the presentation order of the intruders, (2) the orders of procedure modality (human or avatar), and (3) the type of SDP measurement (active or passive).

Immersive virtual reality system

The HTC Vive Virtual Reality System included a wired head mounted display (HMD), two sensors mounted on tripods, and two handheld controllers. This HMD system displayed a neutral room within which avatars could be placed at different distances from the subjects, and then walk towards the subjects while maintaining eye contact (i.e., in the passive SDP), or to remain stationary while subjects walked towards them (i.e., in the active SDP). Personal space measurements were collected using a custom-designed program (Productive Edge; https://www.productiveedge.com/ ), generated on a Unity engine, running on a SteamVR platform. The virtual display was stereoscopic, with a resolution of 1080 × 1200 pixels per eye, with a 110° field of view and a refresh rate of 90 Hz.

Distance range measurements

Based on the above measurements of personal space size (also referred to as ‘interpersonal distance’ here) collected using the active SDP procedure, 5 percentages (25%, 50%, 100%, 200% and 400%) of the subject’s average personal space size were calculated for each subject, and for each modality (averaged over the two genders). The active SDP measurements were chosen for these calculations, instead of the passive SDP values, because of the slightly greater reliability in the former measurements (see below). Then the human and avatar intruders were presented to the subjects at these five distances (real and virtual distances, respectively), in a counterbalanced, pseudorandomized order.

For each modality (human and virtual), the same procedure was conducted twice (using the same order of modality, human or virtual first), for a total of 4 presentations. During the first two presentations, skin conductance responses (SCRs) to an intruder were measured. During the second two presentations, the subjective levels of discomfort were rated by the subject. This fixed order of measurements (with SCR measurements followed by the discomfort ratings) was chosen to minimize habituation of the SCRs to the stimuli, and to avoid potentially confounding effects of the subjective ratings on the SCRs. In the first two presentations (to measure SCRs), each distance was repeated twice per intruder in each modality (real and virtual; the order of which was counterbalanced across subjects). In the second two presentations (to measure subjective ratings), each distance-by-intruder combination was presented once. The overall sequence of procedures and experimental design is shown in Supplementary Figure S1.

To both human and avatar intruders, the experimental timing was as follows: (1) eyes closed, (2) control presentation of empty room (real or virtual), (3) eyes closed, (4) experimental presentation of the intruder in the room (real or virtual), and repeat. The intertrial interval before and after the “eyes closed” conditions was systematically varied, with a mean of 5 s. During the SCR trials, the subjects were instructed to begin with their eyes closed, then to open their eyes for 5 s to a blank room, in which no intruder was present. This inter-trial interval allowed physiological responses to return to baseline between trials. Subjects were then instructed to close their eyes again, and then to open them when cued, at which time an intruder was presented at a given distance. This opening and closing of the eyes was used to avoid possible artifacts due to movement of the human intruder re-positioning themselves within the room. The subject was then instructed to stand still during the presentation of the intruder, and to maintain eye contact for a duration of 10 s, as cued by study staff. During the second (discomfort ratings) trial, subjects were also asked to open and close their eyes, without any blank room condition. When subjects opened their eyes to view the intruder, they were asked to rate their agreement to 3 statements (“I want to move away”, “I am making this person uncomfortable” and “This person is making me uncomfortable”; order counter-balanced across subjects) on a Likert scale ranging from 1 to 5 (1 = agree not at all; 5 = agree very much).

Prior to beginning the Distance Range experiment, two 11-mm Ag/AgCl sensors filled with isotonic paste were placed 14 mm apart on the hypothenar surface of the subject’s non-dominant hand. Skin conductance level (SCL) was measured (in micro siemens) using the MP150 data acquisition system (BIOPAC Systems, Inc., Goleta, CA) at a sampling rate of 2000 Hz, in analogue format, then digitally resampled to 125 Hz before analysis. An event marker was placed at the start of each stimulus trial to allow for measurement of SCL before and after stimulus presentation. SCR amplitude was calculated for each trial by subtracting the mean SCL 1 s before stimulus presentation from the peak of the SCL during the stimulus presentation. We chose to use this simple standard approach, focusing on capturing the amplitude of the response to each stimulus, corrected for possible drifts in SCL due to prior stimulus trials, because it requires no assumptions or models and has been used extensively in prior studies 46 , 47 , 48 .

Statistical analyses

Pearson’s correlations were calculated to compare personal space size across SDP measurements and the two SDP modalities (real and virtual). For the Distance Range measurements, repeated measures ANOVAs were used to test for differences in discomfort ratings (conducted using the average of the ratings for the three statements at each distance, to limit the number of statistical tests) and SCRs within and across modalities and across the personal space distances. These ANOVAs were followed by post-hoc paired samples t-tests. Significance values were corrected for multiple comparisons (Bonferroni), within each comparison.

Most of the data collected in this study were normally distributed. However, several distributions were slightly skewed, such as the personal space size data collected using the active Stop Distance Procedure in the reference cohort of 30 subjects. However we chose to use parametric tests throughout, given that normality requirements can be relaxed for data with the sample sizes of this study 49 , 50 , 51 and because this approach facilitates comparisons across the different portions of our data and with the findings of related studies also using parametric tests.

Model fitting

The SCR and subjective rating data as a function of distance to intruder were modeled using three different curves, all of which were strictly decreasing functions. They include a power law function \(\left(f\left(x\right)=a {x}^{-b}\right)\) , an exponential function \((f(x)=a {e}^{-bx})\) and a logarithmic function \((f(x)=a-b\mathrm{ log}\left(x\right)\) . In each case, \(f(x)\) represents the variable of interest (SCR or subjective rating), \(x\) is the distance from the intruder, and \(a,b\) are pararameters (positive real numbers) to be inferred from the data, using a least square method. As an index for ‘goodness of the fit’, the normalized Root Mean Square (RMS) error was reported in each case. The RMS error was defined as \(RMS=100 \sqrt{\frac{1}{n}{\sum }_{i=1}^{n}{\left(\frac{{y}_{i}-f({x}_{i})}{{ y}_{i}}\right)}^{2}}\) , where \({x}_{i}\) is the \(ith\) distance, \({y}_{i}\) is its corresponding \(ith\) measurement (SCR or subjective rating), and \(n\) is the total number of data points. The coefficient 100 was added to represent the RMS of Error as a percentage.

Within-subject measurements of personal space

These experiments relied on extensive within-subject measurements, in order to increase the signal/noise ratio for each measurement. To test whether such repeated measurements would remain stable over time, we measured the reliability of SDP measurements of personal space size in 30 subjects, with human intruders only. In one session, only passive measurements were collected. In another session, active and passive measurements were collected. The order of passive and active measurement (and the order of intruder gender) was counterbalanced pseudo-randomly across subjects. For each SDP measurement type (passive vs. active), personal space size (i.e. the preferred interpersonal distance) was measured six times.

As illustrated in Fig.  3 a, we found that the personal space size measured in a given subject (relative to a given human intruder) was relatively stable across all six trials, particularly for the active SDP measurements. For instance, the correlations across all active SDP measurements were high (all r > 0.929), and the average of first and last (sixth) measurements were statistically identical to each other (first distance = 55.7 cm ± 4.09; last distance = 54.5 cm ± 3.6) (Fig.  3 b). Nevertheless, consistent with past studies, we observed wide variability in personal space size across individual subjects (e.g., mean active personal space size = 63.3 cm, s.d. = 25.2 cm). Because of the high reliability of values within each subject, and the considerable variability between subjects, we chose the SDP measurements collected using the active procedure to calculate the personal space increments for each subject used in the Distance Range experiment (see below).

Measurements of personal space size are highly reliable within subjects, but vary across subjects. ( a ) Examples of multiple measurements of personal space size, from six subjects, using the passive Stop Distance Procedure (SDP). Data from each subject is shown in a given unique color, arbitrarily chosen for each subject. The SDP values of personal space size remained quite stable across the six trials for each individual subject. ( b ) Group-averaged personal space size (n = 30), measured using the passive SDP (see the dotted line (Session 1) and the dashed line (Session 2, occurring 2–3 days later)), and using the active version of the SDP (see the solid line; Session 2). Again, these group-averaged SDP data show that personal space size is stable over time, and measurements collected using the passive SDP are consistently larger than those collected using the active SDP. Error bars represent one standard error in each direction.

In the SDP measurements collected using the passive procedure, we found that the personal space size values were slightly higher in the initial two trials, then quickly stabilized. For instance, in the average passive SDP values shown in Fig.  3 b, the mean in the third trial was 10.47% less than that in the first trial. However, after stabilization (e.g. trials 4 through 6), differences across trials were not significant (all p  > 0.112), and the correlations across those last three trials were high (all r > 0.957).

Overall, these results suggest that extensive repetition of measurements of personal space size within a given subject do not evoke progressively weaker responses. That is, we found no habituation of the response due to familiarity or diminished orienting/attentional effects, at least beyond the initial trials. These data suggest that personal space is regulated in a relatively stable manner, in response to a given intruder.

Personal space relative to human vs. avatar intruders

Several experiments using virtual reality (VR) environments have suggested that virtual human-like ‘avatars’ can evoke responses related to personal space regulation that may be similar to such responses to real human subjects, even though such avatars are clearly distinguishable from humans 17 , 19 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 . However, the extent to which the properties of such personal space responses to avatars corresponds to those to humans, in otherwise similar contexts, remains unresolved.

Figure  4 and Supplementary Figure S2 show the relationships between the experimental SDP measurement (passive vs. active) and the experimental intruder type (human vs. avatar). For both humans and avatars, measurements of personal space size were larger when measured using the passive compared to the active SDP procedure (humans: t = 5.376, p  < 0.001; avatars: t = 3.547, p  = 0.002), consistent with prior work 54 (but see 19 ). Critically, the measured personal space size to avatars was highly correlated with those to humans (passive: r = 0.734, p  < 0.001; active: r = 0.704; p  < 0.001).

Personal space size measured to human intruders (y axis) is highly correlated with the personal space size measured to virtual intruders (x axis). Each dot represents the average personal space size measured in each subject using the Stop Distance Procedure (SDP) (n = 19). Panel ( a ) shows the correlation in the passive SDP measurements, and Panel ( b ) shows the correlation in the active SDP measurements.

Discomfort ratings across a range of interpersonal distances

The above data are based on measurements of personal space using the SDP, which is a threshold measurement of discomfort 11 , 12 . However, it is now well recognized that discomfort levels vary with distance from an intruding person, when those distances are within the personal space threshold defined by the SDP.

To measure variation in discomfort relative to this personal space threshold, we presented human and avatar intruders at five systematically-varied distances from the subject. These distances corresponded to 25%, 50%, 100%, 200% and 400% of the personal space size that was defined earlier in each subject, based on the active SDP procedure. For avatar-based intruders, the binocular disparity and the head size were calculated and presented to match those of real humans at a comparable distance range. During each trial, the subject was asked to rate their agreement to three specific statements to quantify their subjective level of comfort. The discomfort ratings to each question at each distance for both human and avatar intruders are shown in Supplementary Figure S3, and the average responses to the three questions are shown in Fig.  5 .

Discomfort ratings across a range of distances, normalized to individual personal space size. Group-average (n = 19) ratings of discomfort (the average of ratings of three statements, see text), on a Likert scale of agreement ranging from 1 (‘not at all’) to 5 (‘very much’), to variations in the distance (as a percentage of the personal space size of each subject) (x axis) in response to humans (solid line) and avatars (dotted line). Discomfort ratings were highest for both humans and avatars presented at the closest distance (25% of personal space size). Conversely, the discomfort ratings were lowest to both humans and avatars (at and near baseline of 1 = lowest possible ratings) when presented at distances further than the personal space boundary, i.e. 200% and 400% of a given subjects’ personal space size.

Overall, we found little difference among the responses to the three questions, compared to their average, for both the humans and avatars. A repeated measures ANOVA revealed no significant main effect of SDP modality (real vs. virtual, F = 0.516, p  = 0.482) but revealed a significant main effect of distance (F = 5.873, p  < 0.001; see Supplementary Table S1 for additional ANOVA results). This effect was due to significantly higher discomfort ratings at the closer distances (25%, 50%) compared to the personal space boundary (100%) and beyond it (200%, 400%), in both modalities (see Supplementary Table S2 for pairwise t-test results). Responses at the ‘baseline’ values, outside of personal space (200% and 400%), did not differ significantly from each other, in either the real and virtual modalities. Lastly, a modality by distance interaction (F = 4.375, p  = 0.003) resulted from non-significant trends towards differences between the responses to real vs. virtual humans at the 25% and 200% distances (Supplementary Table S1 ).

Taken together, these results are most consistent with the model shown in Fig.  1 d. These results do not support a two-armed V-shaped function, which is a defining feature of the social equilibrium model; Fig.  1 e) 19 , 27 .

Model testing of ratings data

To model the fall-off of this discomfort-by-distance function, we fit three different monotonically decreasing functions to the average discomfort ratings as a function of the distance between subjects and intruders. In the responses to both humans and avatars, the fall-offs were better fit by a power law function (Root Mean Square (RMS) error of the fit = 10.37% and 12.92% for humans and avatars, respectively), compared with either an exponential (RMS error 15.70% and 16.97% for humans and avatars, respectively) or a logarithmic function (RMS error 19.64% and 31.32% for humans and avatars, respectively (Fig.  6 ).

Model fitting of discomfort ratings data. Average ratings of discomfort (y axis) as a function of personal space size (in %, on the x axis) to either human (left panel) or avatar (right panel) intruders. In both panels, the data is shown as a white dotted line. Brackets indicate one standard error. Three possible functions were tested to model the average fall-off of comfort ratings, including exponential (blue), logarithmic (green), and a power law (red). The power law function produced the best fit.

Moreover, to both humans and avatars, all three functions showed a superior fit to scales of interpersonal distance, rather than to absolute distance. For instance, for the power law fit, the RMS error for the absolute distance = 28.99% and 28.76% for humans and avatars, respectively, compared to the RMS error for interpersonal distance = 10.37% and 12.92% for humans and avatars, respectively. This supports the hypothesis that these discomfort responses reflect gradations in interpersonal distance (i.e. normalized to each subject), rather than absolute distance.

Skin conductance responses across a range of interpersonal distances

It has been suggested that the discomfort evoked by personal space intrusions might manifest itself in physiological variations of the skin conductance response (SCR) at correspondingly different interpersonal distances, given that SCR is thought to reflect variations in ‘arousal' 59 , 60 , 61 , 62 , 63 , 64 , 65 , based on sympathetic nervous activity. Given that expectation, we also measured whether (or how closely) such SCR responses to avatars would match those to the human subjects, as a further test of our rough sketch model.

We measured SCR amplitudes to presentations of both humans and avatars, over the same distance range tested above, i.e. 25%, 50%, 100%, 200% and 400% of each subjects’ individual personal space. Following data collection, one subject was excluded as an outlier based on a priori criteria (average skin conductance responses outside of 1.5* interquartile range); thus these analyses are of data collected from the remaining 18 subjects. The stimuli were identical to those used in the rating measurements. We measured and averaged the SCRs across 4 or 8 trials per distance, relative to the real humans or avatars, respectively.

We found that the SCR functions in response to humans and avatars (Figs.  7 and 8 ) were similar to each other, and also similar to the discomfort rating functions (Figs.  5 and 6 , and Supplementary Fig. S3). Supporting this observation, a repeated measures ANOVA revealed a main effect of distance (F = 17.116, p  < 0.001), with no main effect of modality (real vs. virtual; F = 0.146, p  = 0.707) or modality by distance interaction (F = 0.294, p  = 0.881). Follow-up paired sample t-tests showed no differences between SCRs elicited by humans vs. avatars at each distance (all p  > 0.2; see Supplementary Table S1 ). Also, within each modality (real and virtual), significantly higher SCRs were found at the closer distances (25%, 50%) compared to the further ones (100%, 200%, 400%), and there were no significant differences between the SCRs elicited at any of the further distances (200% vs. 400%, 100% vs. 200%, and 100% vs. 400%; see Supplementary Table S3 for pairwise t-test results).

Average skin conductance responses across a range of distances, normalized to individual personal space size. The top panels show the average time courses of skin conductance levels measured in response to humans (panel a ) and to avatars (panel b ), when presented at different percentages of each subject’s personal space size. The bottom panels show the average peak skin conductance response amplitudes (‘arousal level’) across five percentages of personal space size (x axis), for humans (solid line) and avatars (dotted line), plotted on a linear axis (panel c ) and on a logarithmic axis (panel d ).

Model fitting of skin conductance responses. SCR peak responses (y axis) as a function of personal space size (in %, on the x axis) in response to either a human (left panel) or avatar (right panel) intruder. As in the ratings data, the averaged SCR response (dotted white line) was best fit by a power law (red), compared to either an exponential (blue) or a logarithmic (green) function.

Model testing of SCR data

As in the ratings data, we found that the fall-off in SCR values to both human and avatar intruders was well fit by a power function (RMS error 18.43% and 18.57% for humans and avatars, respectively), and less well fit by an exponential (RMS error 39.39% and 43.57% for humans and avatars, respective) or logarithmic function (RMS error 39.02% and 53.02% for humans and avatars, respectively (Fig.  8 ).

Consistency across the data and effects of physical features

To highlight the consistency across the two measurements in the discomfort-by-distance functions, in responses to both humans and avatars, both the discomfort ratings and SCR data are shown in Fig.  9 .

Similarity of discomfort ratings and skin conductance responses, to humans and avatars. The discomfort ratings are shown in green and the SCRs are shown in red. The ratings and SCRs to humans and avatars are displayed with solid and dashed lines, respectively. The minimum rating was 1, so the baseline values (further than the averaged personal space, e.g. at 200% and 400%) was near (but slightly above) 1. In the SCR measurements, the baseline values averaged near 0.4 microSiemens. Both the rating and SCR scales are linear. The scaling of ratings to SCR was otherwise arbitrary.

Lastly, we found no statistically significant correlations between measurements of arm length or span and the personal space (SDP) measurements, the discomfort ratings or the SCR data.

Overall, this study found little or no significant differences between the interpersonal distances measured in response to real and virtual human intruders. This similarity in personal space with respect to humans and avatars was confirmed in extensive measurements of rated discomfort levels across a range of interpersonal distances, including those closer and further than each subject’s personal space boundary. This decrease in comfort at distances closer than the personal space boundary (i.e. the ‘fall off’ in discomfort at increasing distances) was well fit by a power law, for the responses to both humans and avatars, and for both psychological (ratings) and physiological (SCR) measurements.

These results suggest that responses to simulations of humans (avatars) at different virtual distances share neural mechanisms with those involved in responding to real humans at corresponding actual interpersonal distances. Such evidence for shared neural processing supports the hypothesis that the brain performs a ‘rough sketch’ of personal space at an early stage of information processing.

Variations in discomfort across interpersonal distance

The classic stop distance measurements of personal space described above define a (binary) threshold response, i.e. a specific distance at which the subject begins to feel uncomfortable in response to an intruder. At distances that are progressively closer than that threshold-defined personal space size, many prior studies (and the data here) show that the level of discomfort increases accordingly. Prior studies have reported that this gradient is linear with personal distance (with strong non-linear contributions) 24 , or logarithmic 59 , or one arm of a wider ‘V’ shaped function 19 , 27 .

Here, the fall-off was well fit by a simple power law, in both discomfort ratings and skin conductance data. Accordingly: (1) the highest responses occurred at the closest distance tested (25% of personal space); (2) the lowest (baseline) responses occurred at the furthest distances tested (200 and 400%); (3) the function approached baseline near the behaviorally-defined personal space boundary (100%); and (4) intermediate responses were found at an intermediate distance (50%).

Stevens 66 formulated the quantitative relationship between the perceived magnitude of a stimulus and its physical intensity as a power law. That relationship became known as a “fundamental law of psychophysics” 67 , which has been confirmed empirically in multiple sensory systems and tasks. For instance, in the visual system, a power law function has been attributed to the relationship between stimulus luminance and brightness, the physical size of an stimulus and its perceived size, the purity of a hue and its saturation, and several other attributes of visual stimuli and their perceived magnitude 68 . Physiologically, power law relationships have been demonstrated in neural activity across different scales, ranging from the firing rate of single neurons in visual cortex in response to stimuli with different intensities, the number of neurons activated by stimuli with different intensity levels 69 , the relationship between luminance and visual-evoked potential latency 70 , and even to the relationship between cognitive complexity (numerosity) and neural activity in the prefrontal cortex of monkeys 71 .

The mechanistic roots of the power law relationship can be inferred from the activity of the neuronal substrate at various levels. At the level of a single neuron, a noisy linear-threshold function can account for the power law relationship between the input voltage and the firing rate of a neuron 72 . At the level of neural circuits, a power law nonlinearity can arise from an interaction of neurons with nonlinear sigmoid activation functions through a feedback loop 73 . At the level of neural ensembles, power laws can arise from averaging multiple independent exponential decay processes 74 . More generally, power laws, being quite common in biological systems 75 , can arise from the properties of self-organized critical systems that are far from thermodynamic equilibrium 76 .

Thus, power laws are common in models of sensory systems, and the evidence here for power law responses to personal space intrusions is broadly consistent with our rough sketch model of personal space, at early (e.g. more sensory-dominated) stages of computation.

It is also broadly consistent with evidence from fMRI studies for increases in activity in areas of parietal cortex and closely connected brain regions in response to images of human faces that are located within, but not outside of, virtual personal space 77 ; the amplitude of this response is proportional to the proximity of the stimulus. Additional work can reveal whether such fMRI responses also follow a power law function.

Within-subject and between-subject variability in personal space

It is well established that SDP measurements based on absolute distance vary significantly between individuals 11 . To account for this variation, Hayduk 24 argued that it is helpful to normalize (or ‘proportion’) personal space measurements across individuals. Consistent with this, we found that such a normalization yielded data that was more consistent across individuals, and less noisy, compared to variations in absolute distance. This scaling of interpersonal vs. absolute space implies that a specific set of brain mechanisms are engaged to calculate and regulate personal space in all subjects, but that the values in a given subject scale by a constant.

In contrast to the wide variation between individuals, we found high reliability within subjects, in repeated measurements of stop distance, with a mean inter-trial reliability of r  = 0.879 (lowest correlation of 0.763) among all six trials of passive and six trials of the active SDP measurements. This high reliability is consistent with prior studies, which reported an inter-trial reliability of r  = 0.81 24 , 78 . Although the measurements of the passive SDP task showed slightly higher initial values, the small increase in the passive mean SDP scores may arise because in the passive (but not the active) condition, subjects anticipated an impending personal space intrusion, which could be avoided only by saying ‘stop’. Thus, slightly earlier ‘stop’ commands resulted in a slightly larger personal space size, perhaps reflecting a more general contribution from threat detection mechanisms, in addition to basic mechanisms regulating personal space. Regardless, the near-constant values evident in the active condition, and after stabilization in the passive version, suggest that repeated conventional measurements of personal space size reflect surprisingly little or no habituation. Other studies have also reported that values of personal space size are highly replicable over time, over durations ranging from 1 to 60 s 79 , to multiple weeks between measurements 80 . Based on these data, Hayduk 78 concluded that “there are few social science phenomena that can be measured as precisely as personal space”.

Here, the high reliability of personal space measurements was important for two reasons. First, this property was crucial in order to reduce experimental noise by extensive signal-averaging, based on the Central Limit theorem. Second, the high reliability also supports our hypothesis that lower stage (near-sensory) brain sites calculate a rough sketch at an early stage of the personal space calculation. In visual cortex, many responses are relatively stereotyped over numerous repetitions, whereas activity of higher stage, cognitive areas is more likely to habituate.

Alternative models of personal space

Essentially all models of personal space posit a zone immediately surrounding the subject into which intrusion by another person evokes discomfort (see Fig.  1 ). In addition, a ‘social equilibrium’ model’ 27 further proposed a second zone of increasing discomfort in response to persons that are located further (rather than nearer) than the conventionally-defined personal space boundary 25 , 26 (Fig.  1 e). This hypothetical second zone of increased discomfort has been termed an ‘extrusion’ zone 19 , 24 . A recent study reported experimental evidence for such a discomfort-producing extrusion zone, based on higher ratings of discomfort found both within and outside of the personal space boundary 19 . Here, we did not find evidence for such an extrusion zone, even though our measurements spanned a larger range of absolute distances than this prior study. Perhaps differences in contextual factors or task instructions account for the presence or absence of an extrusion effect. For example, if discomfort ratings in prior studies reflected responses to violations of social norms for interpersonal distances, subjects may have reported some subjective discomfort at distances outside of their expected personal space boundary.

This unresolved question bears specifically on our understanding of experiences of social distancing during the COVID-19 pandemic. The existence of an extrusion zone would predict that standing at pandemic-related social distances (e.g. 2 m) would induce additional discomfort, compared to standing at typical interpersonal distances 81 . However if there is no extrusion zone, no increase in discomfort would occur during social distancing.

A rough sketch of interpersonal distance

Based on the results described here, we propose that the neural calculation of personal space includes an imprecise initial value of personal space size (i.e. a rough sketch) at an early stage of spatial encoding. Single-neuron recording in monkeys 38 , 40 , 82 , behavioral studies 39 , neuropsychology 40 , 83 , 84 , 85 , 86 , and fMRI results in humans 35 , 37 , 87 suggest that such an initial stage of personal space computation might involve parietal cortex. Our general hypothesis is that the eye-centered spatial encoding in visual cortex is integrated into a broader body -centered or ego-centered) spatial mapping in/near inferior parietal cortex. Such a body- (or person-) centered coordinate system could be used as an initial substrate for mapping personal (as well as non-social) space.

An implied corollary of this hypothesis is that this rough sketch is communicated to higher stage cortical areas which fine-tune that initial value of interpersonal distance, based on more subtle cues (e.g. whether the intruding object is a real human, and of which gender, whether presenting in an aggressive or welcoming stance, etc.). By design, our experiment focused on testing for the proposed initial rough estimate of personal space size; thus we deliberately reduced variations in higher stage variables.

Our model is broadly analogous to the ‘2 ½ D’ model of visual cortical processing, as proposed by Marr and colleagues 88 , 89 . In that model, lower level visual cortical mechanisms first generate an approximation of visual objects (a “2 ½ D” sketch), which is then further modified at higher computational (or brain) stages to yield the more detailed images which we ultimately ‘see’ in 3D. Related models also proposed that visual cortical inputs are processed more grossly (roughly) at lower levels, then more specifically at progressively higher levels of visual cortex 90 , 91 , 92 , 93 , 94 .

This ‘rough sketch’ model may also apply to other systems. For instance, in one form of the “rubber arm illusion”, a person’s real arm is hidden, and a slightly displaced artificial arm and fingers (generated using either rubber prosthetics, or programmed in virtual VR) is presented, to generate feelings of ‘ownership’ of that artificial arm, including protective responses to it 95 , 96 , 97 , 98 , 99 , 100 , 101 . Typically, the artificial arm can be easily discriminated from the subject’s real arm by direct inspection (since it is either an imperfect rubberized dummy or a slightly blurry, pixelated image viewed through VR goggles). Nevertheless, analogous to the results reported here, a subject’s perception can still be fooled by the approximate representation of the arm, eliciting responses ‘as if’ it were a real arm.

Another example of this effect is seen in studies using experimental achromatic images of human faces mimicking specific emotional expressions, that aim to generate responses akin to the corresponding emotions in the viewer 102 , 103 , 104 , 105 , 106 . Again in this case, the subject typically correctly perceives the emotional faces as simulated rather than real—but nonetheless experiences automatic, affective responses to them.

Necessary and sufficient information for eliciting a ‘Rough Sketch’ response

Several prior studies using VR have tested for related properties of personal space regulation with respect to avatars and humans, as in the current study. However, some of these studies have reported differences between interpersonal distances (stop distance values) measured to humans when compared to those measured to inanimate human-like intruders, including plastic mannequins 17 , robots 54 , or more rudimentary avatars 55 , 107 . Additional experiments will be required to define the specific features of human-like avatars which must be present to evoke a need for personal space.

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This work was funded by NIMH (RO1MH109562, to DJH) and the Research Scholars Program of the Executive Committee on Research of Massachusetts General Hospital (DJH).

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Tootell, R.B.H., Zapetis, S.L., Babadi, B. et al. Psychological and physiological evidence for an initial ‘Rough Sketch’ calculation of personal space. Sci Rep 11 , 20960 (2021). https://doi.org/10.1038/s41598-021-99578-1

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The anisotropy of personal space

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Validation, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliation Department of Psychology, Johannes Gutenberg-Universität Mainz, Mainz, Germany

Roles Conceptualization, Supervision, Writing – review & editing

Roles Conceptualization, Resources, Supervision, Writing – review & editing

• Robin Welsch, 
• Christoph von Castell, 
• Heiko Hecht

• Published: June 4, 2019
• https://doi.org/10.1371/journal.pone.0217587
• Reader Comments

Violations of personal space are associated with discomfort. However, the exact function linking the magnitude of discomfort to interpersonal distance has not yet been specified. In this study, we explore whether interpersonal distance and discomfort are isotropic with respect to uncomfortably far or close distances. We also extend previous findings with regard to intrusions into personal space as well as maintenance of distances outside of personal space. We presented subjects with 15 interpersonal distances ranging from 40 to 250 cm and obtained verbal and joystick-based ratings of discomfort. Whereas discomfort rose immediately when personal space was entered, the gradient was less steep for distances that exceeded the comfort region of personal space. Thus, personal space is anisotropic with regard to experienced discomfort.

Citation: Welsch R, von Castell C, Hecht H (2019) The anisotropy of personal space. PLoS ONE 14(6): e0217587. https://doi.org/10.1371/journal.pone.0217587

Editor: Rick K. Wilson, Rice University, UNITED STATES

Received: January 24, 2019; Accepted: May 14, 2019; Published: June 4, 2019

Copyright: © 2019 Welsch et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript and its Supporting Information files.

Funding: The authors received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Introduction

As a stranger approaches us, there comes a point where we start to feel uncomfortable and intruded upon. Our feeling of an inappropriately large or short distance with respect to another person can be conceived of as a personal space (PS) requirement accompanied by a feeling of psychological distance. How PS extends and shapes distance-behavior has first been studied in animals. For example, animals in captivity claim a relatively smaller territory and flight zone, as compared to wild animals [ 1 ]. Sommer [ 2 ] pioneered proxemic research in humans. He observed that when interacting with others in a hospital, schizophrenic patients claimed a larger portion of space to themselves as compared to non-schizophrenic patients. Hall [ 3 ] took up the idea of interaction distances and proposed four distinct spaces by their radius, mainly based on the appropriateness of potentially available sensory perceptions: intimate space (0–45 cm), personal space (45–120 cm), social space (120–365 cm), and public space (365–762 cm). These ranges have been replicated within a large set of different nationalities and cultures [ 4 ], in various measures of interpersonal distance (IPD, [ 5 ]) as well as in virtual environments [ 6 – 9 ].

The most prominent definition of PS stems from Leslie Hayduk [ 10 ]: „… we can define personal space as the area individual humans actively maintain around themselves into which others cannot intrude without arousing discomfort.“(p.118). This definition structured proxemic research and improved the conceptualization, the measurement of PS, and the identification of correlates.

Measuring and conceptualizing PS

Attempts to refine the concept of PS have confronted the issue of measuring the shape of PS. For example, Hecht et al. [ 7 ] let participants approach both a real and a virtual confederate from multiple angles while measuring the preferred IPD. They could show that PS is approximately circular, both in real and virtual environments. Thus, in line with the definition of PS [ 10 ], personal space forms a circular area surrounding the person.

A large set of personal and contextual determinants of the size of PS could be identified [ 5 ], mainly due to the development of the stop-distance paradigm. Williams [ 11 ], a student of Sommer, let a confederate walk up to a subject until the subject deemed the distance to be most comfortable for conversation, and signaled the confederate to stop. The resulting IPD was measured as an approximation of the size of PS. This approach to PS has since been adopted in proxemic research, with some minor variations, which include subjects actively approaching the experimenter or a confederate [ 12 ], or projective techniques such as chair placement [ 13 ].

Although the stop-distance procedure appears to be the most reliable and valid approach [ 5 ], studies differ greatly in the average size of PS. Some studies found strangely short preferred IPDs at about 35 cm, [ 14 ] or quite large IPDs with more than 120 cm [ 9 , 15 , 16 ]. This is problematic in many ways. Firstly, it is particularly hard to compare absolute IPDs among studies and measurements. Secondly it makes PS indistinguishable from other related constructs such as extra-personal monitored space far from the individual, or peri-personal space, a near-body space with protective and connective functions [ 17 ]. Thirdly, if PS size ranges spontaneously at about 65 cm, as Hall [ 3 ] proposed, then the applicability of proxemics for purposes of human factors, such as interior design or safety zones in public places [ 18 ], or clinical diagnostics [ 19 , 20 ] would be quite limited. The first issue addresses a problem of reliability, the latter two problems concern construct validity of preferred IPD as a measure of PS size.

Hayduk [ 5 ] has attempted to address the issue of reliability by comparing test-retest correlations in a multitude of studies. For IPD, as measured by the stop-distance paradigm, this reliability was particularly high, at about .81. However, this concerns only the stability of rank-orders and differences within the sample, which cannot address why measurements seem to differ on an absolute scale. With that in mind, the first aim of our study was to quantify absolute reliability, the degree to which the measurements deviate on an absolute scale [ 21 , 22 ]

IPD and discomfort

The latter part of Hayduk's defintion of PS, stating that intrusion of PS elicits arousal and discomfort, has not been sufficiently investigated. Studies in this domain have merely sampled a few points of the IPD continuum [ 23 – 25 ] and did not compare specific functions, which would be needed to gain insight into how discomfort rises as a person feels intruded upon. For example, Hayduk [ 24 ] let subjects estimate three distinct points of uncomfortableness to illustrate an intrusion-discomfort relationship. Subjects walked towards a confederate and told the experimenter when they felt slightly, moderately, or very uncomfortable. Distances for those three points showed an increase of uncomfortableness associated with intrusion into PS. This is in line with equilibrium-theory, which suggests that preferred IPD can be seen as an equilibrium of approach and avoidance forces regulating the level of intimacy [ 26 ]. Any deviation from the equilibrium-point should increase discomfort. This suggests that outside of PS, discomfort should increase again. Note that the notion of discomfort when moving away from a person does presuppose an action goal to interact with this person. The social situation should be standardized such that the action goal can be considered constant.

For lack of a good term, we refer to a position too far from the equilibrium point as extrusion. We hypothesize that intrusion and extrusion will both reduce the subjective comfort of the subject. The question is whether discomfort rises asymmetrically as one moves away from the comfort spot or equilibrium-point toward intrusion or toward extrusion. As there is more room for extrusion, we would expect the gradient to be shallower in extrusion cases compared to intrusion.

To our knowledge, there are no published studies that provide a clear answer to this question, although several attempts have been made to measure comfort. For example, Thompson et al. [ 27 ] manipulated IPD between people interacting in video scenes and asked subjects to judge comfort and appropriateness of the distances depicted. They found large (300 cm) and short distances (between 0 and 180 cm) to be less preferable, as compared to intermediate distances (180–240 cm), which were rated as most pleasant. Their findings suggest that there is some tolerance space around the preferred distance [ 28 , 29 ]. This tolerance for violations could possibly explain why IPD differs in active and passive stop-distance tasks. In Iachini et al. [ 30 ], passive approaches by the confederate, whom the subject signaled to stop, resulted in larger distances as compared to approaches where the subject walked towards the confederate. Alternatively, the differences could be due to poor reliability of the IPD measure. Thus, the active approach used in a stop-distance task should be supplemented with a passive approach, and it should be replicated. Against this backdrop, the second aim of our study was to examine the function of IPD in relation to discomfort using the stop-distance task in both active and passive approaches.

We recruited 24 subjects at the University of Mainz aged from 18 to 28 years ( M = 21.66, SD = 6.92, 6 male), with an average body height of 170.96 cm ( SD = 7.25 cm). Prior to testing, they gave written consent in accordance with the declaration of Helsinki and filled out a demographic questionnaire. Prior to the study, the Institutional Review Board (IRB) of the Institute of Psychology at the University of Mainz had informed us that in accordance with the department's ethics guidelines no explicit ethics vote of the IRB was necessary for our study, because we designed the experiments to test healthy adult volunteers, to present only harmless visual stimuli, to rule out physical or psychological stress, and to refrain from measuring physiological parameters. We did not intend to collect sensitive data like personality or clinical scales, or to provide misleading or wrong information to participants. All subjects reported their acquaintance with the confederate (good friend–mere acquaintance—stranger). All participants rated the confederates to be strangers. They had normal or corrected-to-normal visual acuity (Snellen fraction 1.0 or larger) as measured by the Freiburg Acuity Test [ 31 ] and they received partial course credit for participation.

Design and stimuli

Subjects were placed at 15 frontal IPDs to a confederate varying from 40 cm to 250 cm in steps of 15 cm, which corresponds to the mean minimum and maximum distance for conversation obtained by Williams [ 11 ]. These distances were marked–but not labelled–with tape on the floor. On a given trial, both subject and confederate were positioned on a random pairing of these marks aligned to their body-center. The body-center was estimated to be the middle of the foot, marked by dots on the shoes. Subjects as well as the confederate were instructed to look straight at each other’s face throughout the whole experiment. The two confederates taking part in this study were both young females. One of the confederates was 165 cm in height and had blond hair, the other was 167 cm tall and had brown hair. The two confederates took turns between sessions in order to counteract potential confounding variables, i. e. fatigue, poor concentration, etc. Both confederates wore a white shirt and blue jeans, see Fig 1 . The individuals in this Figure have given written informed consent (as outlined in PLOS consent form) to publish this photograph.

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Tape on the floor marked the 15 IPDs.

https://doi.org/10.1371/journal.pone.0217587.g001

For all testing blocks, we standardized the social situation to minimize situational effects on IPD [ 3 ]. Subjects had to imagine a scenario in which they were in an open space in an unfamiliar city asking a stranger for directions. Subjects were placed at 15 different IPDs in a fixed-distance task and were asked to rate subjective discomfort verbally on a rating scale ranging from -100 (maximum discomfort, too close) to 0 (ideal distance) to +100 (maximum discomfort, too far). In Block 1, the subject was directed by the experimenter and the confederate remained stationary. In Block 2, the subject remained stationary and the confederate moved to the respective positions between trials. Subjects were blindfolded during the positioning. After the positioning, the blindfold was lifted and he/she rated subjective discomfort.

Block 3 followed the procedure of Block 2, but subjects rated discomfort by positioning a joystick. This was done to control for social desirability, the confederate was unable to see the exact tilt of the joystick. Subjects were instructed to tilt the joystick away from themselves as a function of experienced discomfort when IPD was deemed too close, or to tilt the joystick towards themselves when the distance was not close enough. All possible orders of Blocks 1, 2 and 3 were used and counterbalanced between subjects. Within each block, the order of distances was randomized.

Next, subjects completed two repetitions of an active and a passive stop-distance task to estimate the preferred IPD. In the active stop-distance task, the subject approached the confederate until comfortable IPD had been reached. In the passive stop-distance task, the subject was slowly approached by the confederate until the subject signaled the confederate to stop. Subjects were allowed to fine-tune this distance by instructing the confederate to adjust forward or backward. Preferred IPD was measured via a tape measure on the floor and recorded as the distance between the subject’s and the confederate’s body center. Order of the passive and active stop-distance task was counterbalanced within the sample. Subjects were tested in individual sessions of approximately 60 minutes. No time constraints were imposed in any of the trials [ 24 ]. After the procedure, the subjects were thanked and debriefed. We report all measures and scale manipulations in this study. We did not exclude any of the experimental trials from data analysis and sample size was not increased after data analysis.

Statistical analysis

To enable the examination of the Null-hypothesis, we have opted for a Bayesian approach to data analysis. The Bayes Factor (BF) is used for statistical inference and is computed using the BayesFactor-package [ 32 , 33 ] in R [ 34 ]. Here, the BF quantifies the relative likelihood of the Null-model as compared to the alternative-model given the observed data. We either provide the likelihood for the Null-model relative to the alternative model (BF 01 ) or the reverse fraction (BF 10 ). Note that we have compared different weakly informative priors in a prior-sensitivity analysis. The choice of priors did not influence statistical inference in this study as the data obtained clearly overwhelmed the priors when computing the Bayes Factors. Thus, we stuck with the default priors of the BayesFactor-package in t -tests, regressions and analyses of variance. We report median estimates of parameters with high density intervals at 95% from the posterior distribution. To model the relation of IPD and discomfort, we calculated a Bayesian linear mixed model (BLMM) using brms [ 35 ], a wrapper for the STAN-sampler [ 36 ] for R [ 34 ]. We applied normally distributed priors ( M = 0, SD = 1) on all beta-coefficients, with Cholesky priors on the residual correlation (η = 1) and a t-distributed prior to allow for thicker tails ( df = 3, M = 0, SD = 10) on the centered intercept, the variance parameters and sigma. These priors are only very weakly informative and mostly help in the regularization of the posterior distributions. We computed 4 Hamilton-Monte-Carlo chains with 10000 iterations each and 20% warm-up samples. Trace plots of the Markov-chain-Monte-Carlo permutations were inspected for divergent transitions. All Rubin-Gelman statistics were well below 1.1. The experimental data and the R code can be found in the Supplementary Material S1 Data and S1 Code. The files provided comprise the minimal underlying data that an independent researcher would need in order to replicate all of our results, conclusions, figures and summary statistics. The files do not contain any personally identifying information.

Reliability of the stop-distance tasks

First, we will consider relative reliability, stability of rank order and differences within the sample, and second, we will consider absolute reliability, which refers to the absolute deviation of sequential measurements.

Difference of IPD from both test and retest as a function of averaged IPD of both tests for every participant (Panel A: active stop distance task; Panel B: passive stop distance task) with mean difference (black line).

https://doi.org/10.1371/journal.pone.0217587.g002

Spontaneous variation was rather small in all tasks, in the range of +/- 10–15 cm, and unrelated to the size of PS. Thus, a change in IPD in this range should be detectable as a violation of PS. To investigate a potential difference in absolute reliability between tasks, we computed a Bayesian two-way repeated measures analysis of variance (BrmANOVA) with the factors approach (active vs. passive) and test (test vs. retest). However, a null-model was more likely to be true given the data than were models with main effects, BF 01 > 4.1 or interaction effects, BF 01 > 18.57. Thus, differences in measurements of test and retest varied unsystematically and not as a function of active and passive approaches. Contrary to Iachini et al. [ 30 ], active and passive approaches did not produce any differences in preferred IPD at all.

Construct validity

The stop-distance task seems to reliably measure the outlines of personal space. But what point does the stop-distance task sample from the continuum of IPD and discomfort? We compared the mean shortest distances that did not elicit any discomfort (Block 1, 2, 3) to the mean IPDs of the stop distance trials (Block 4–5) for each individual, see Fig 3 . A one-way BrmANOVA again favored the null-model against a model that assumed differences in IPD across Blocks, BF 01 > 27.60.

Error bars denote +/- one standard error of the mean.

https://doi.org/10.1371/journal.pone.0217587.g003

Lines denote the different methods of assessment for discomfort applied in the three blocks.

https://doi.org/10.1371/journal.pone.0217587.g004

This plot shows active verbal ratings, passive verbal ratings, and joystick-based ratings of discomfort as a function of IPD. Descriptively, the shape of the discomfort-function aggregated across subjects does not vary across Blocks, indicating that the ratings were unaffected by our manipulation of response modality. Short and large IPDs tended to increase discomfort. A valley in the function occurred at distances around 85 to a 100 cm, which indicates a certain tolerance for violations of PS. However, we entertain that the valley with least discomfort in Fig 4 resembles the between-subjects variance, see the error bars in Fig 3 . It follows that the apparent U-shape could have been produced by the averaging of varying individual V-shaped data. To investigate this potential effect of aggregation across subjects, we inspected the 24 individual curves of all subjects in every Block, and centered these functions on the edge of the individual PS, that is on the shortest individual mean IPD (averaged across the three Blocks) that did not elicit any discomfort (see Fig 4 ). Inspecting the individual centralized functions in Fig 5 , it becomes clear, that the U-shaped pattern observed in Fig 4 appears to be an artifact caused by the aggregation across subjects.

https://doi.org/10.1371/journal.pone.0217587.g005

Unlike previously thought, the response to violations of PS is rather immediate. That is, our data do not support the notion of a tolerance zone around the preferred IPD where intrusion or extrusion is acceptable in the sense that it leaves comfort ratings unaffected. Most importantly, preferred IPD in the stop-distance tasks corresponds to the shortest distance without discomfort in the rating-task. Spontaneous variations in IPD occur in the range of 10–15 cm and seem to be unrelated to the mean IPD (see Fig 2 ). Thus, the stop-distance task is rather reliable and seems to produce a valid approximation of the borders of PS. The tolerance for violations of PS previously observed in other studies [ 27 ], may merely be an artifact of aggregation across subjects, which may mislead into suspecting a larger acceptable range or even a U-shaped function of IPD and discomfort. Note, however, that we cannot rule out a tolerance for violations of PS smaller than 15 cm as we sampled distances in steps of this size. Within this range, spontaneous variations in preferred IPD may occur. Furthermore, we merely sampled distances from 40 cm to 250 cm and found a linear increase of discomfort with deviation from PS, this might not hold for extrusions of more than 200 cm.

An intrusion into PS of 15 cm or more beyond the comfort point leads to an immediate steep increase in discomfort. Movement in the opposite direction away from the other person leads to a likewise immediate but shallower increase in discomfort. Thus, the response to intrusion and extrusion is anisotropic. Equal distances from the border of PS produce unequal increases in discomfort. Intrusion has a steeper gradient than extrusion. Let us substantiate this idea with the example of a conversation between person A and person B. If person A reduces IPD toward person B, the probability for a corrective step by B away from person A should increase immediately. If, on the other hand, person A enlarges IPD toward person B, the probability for a corrective step by B toward person A should likewise increase, but with a lower probability than in the first scenario. Because extrusion of PS does not produce as much discomfort as does intrusion of PS.

In other words, we predict a hysteresis effect in the following sense. We have always used an approach scenario, that is in active and passive approach in which the initial IPD was larger than the ideal IPD. If one were to start the stop-distance task once from a position well within the intrusion zone and once from a position within the extrusion zone, we would expect slightly larger preferred IPD in the latter case.

Note that the anisotropy of PS holds with respect to intrusion/extrusion but not with respect to active/passive approach. Contrary to Iachini et al. [ 30 ], we could not find any differences in active and passive approaches. This could be due to the habituation of subjects to our stimulus. Whereas our confederate completed all experimental trials, their stimuli randomly changed throughout the experiment. Thus, effects of perceived dominance or potential fear of the approaching target, which may be particularly salient in active approach, may have already faded in our experiment. This might also explain the comparatively large (i. e. more conservative) judgments of preferred IPD in their experiments.

Following the examination of the relation of IPD and discomfort, we can qualify some proxemic theories. Preferred IPD has been seen as an equilibrium of approach and avoidance forces regulating the level of optimal stimulation [ 37 , 38 ]. Accordingly, the deviation of IPD from the point of equilibrium has been taken to produce equal discomfort on the intrusion and extrusion side, which was not supported by our data. Sundstrom et al. [ 39 ] as well as Thompson et al. [ 28 ] suggested a U-shaped relation of IPD and discomfort. They also proposed some degree of sluggishness or tolerance for violations of PS [ 40 ]. Short distances from the equilibrium-point should affect discomfort to a lesser degree than large distances. Again, we could not find any support for this prediction in our data.

We like to entertain a different view on PS. We suggest that PS behaves like a dynamically self-constructed space. This space surrounds the person and can be characterized in terms of its shape [ 7 ], elasticity [ 12 ], and density with repelling and attracting forces. Kurt Lewin [ 41 ] has attempted to formalize the notion of psychological spaces in his field theory, wherein human behavior within the environment is characterized by vectors of approach or avoidance forces that tend toward a state of equilibrium [ 26 ]. These vectors are tied to individual perception and constitute non-Euclidian psychological distances that partition the environment into different psychological fields or spaces. Thinking of PS in field-theoretical terms, we may be able to quantify the principles of maintaining and constructing a PS. In the present study, our measure of IPD can be interpreted as the equilibrium-point where approach and avoidance forces on the individual are balanced. The force gradient as one moves away from this equilibrium-point is roughly linear–at least within the distances we have sampled–and it is anisotropic. It is steeper on the intrusion side of the equilibrium point than it is on the extrusion side. This might be because avoidance tendencies tied to intrusions of PS, and approach tendencies related to extrusions, are weighted differently in producing discomfort. Furthermore, approach and avoidance forces are fueled by a large set of determinants in social interactions, such as the urgency of the communication, the level of intimacy, fear, arousal, etc., for a review see Hayduk [ 5 , 10 ]. How exactly approach and avoidance relate to IPD and discomfort is beyond the scope of this study, but future investigations may embark upon this problem from a field-theoretical perspective.

Within this field-theoretical framework, we can generate qualified hypotheses as to the effects of a given person variable or a given environment variable. For instance, it might make sense to hypothesize on the basis of what is known about psychopathy, that the equilibrium-point is unaltered in psychopathic subjects but the gradient is much shallower on the intrusion side than it is in less psychopathic subjects when confronted with social threat [ 12 ]. In contrast, external factors, such as the crowdedness of the space, could merely move the equilibrium-point without affecting the steepness of the gradient. For example, in a crowded market place the equilibrium-point should be closer to the person. Future studies should refine this field-theoretical model and test the novel predictions with regard to discomfort and IPD, which it allows to generate.

Supporting information

S1 data. data of the experiment..

https://doi.org/10.1371/journal.pone.0217587.s001

S1 Code. R-syntax for data analysis.

https://doi.org/10.1371/journal.pone.0217587.s002

Acknowledgments

Agnes Münch programmed the joystick task. We thank Chiara Oftring, Sebastian Laube and Lea Thomas for assisting in the experiment.

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Personal Space, Crowding, and Spatial Behavior in a Cultural Context

Cite this chapter.

• John R. Aiello 4 &
• Donna E. Thompson 5  

Part of the book series: Human Behavior and Environment ((HUBE,volume 4))

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Research interest in the topics of personal space, crowding, and spatial behavior has increased exponentially over the past fifteen years. This growing literature has indicated that the two primary functions served by the use of space are regulation or control and communication. One of the first systematic treatments of this domain was E. T. Hall’s The Hidden Dimension. In his book, Hall (1966) proposed that individuals from various ethnic and cultural backgrounds differ with regard to their spatial behavior, and suggested that these differences were reflective of different cultural norms governing the use of space within different societies. During the last decade, Hall’s ideas have stimulated a considerable amount of research and writing on the description and comparison of differences in the structuring and use of space. Unfortunately, only a small proportion of this research has examined spatial behavior within a cultural context. Nevertheless, this growing body of research has generally been rather supportive of Hall’s qualitative observations.

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Aiello, J.R., Thompson, D.E. (1980). Personal Space, Crowding, and Spatial Behavior in a Cultural Context. In: Altman, I., Rapoport, A., Wohlwill, J.F. (eds) Environment and Culture. Human Behavior and Environment, vol 4. Springer, Boston, MA. https://doi.org/10.1007/978-1-4899-0451-5_5

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The perception of territory and personal space invasion among hospitalized patients

Caroline roveri marin.

1 Department of Collective Health, Faculty of Medicine Jundiaí, Jundiaí, São Paulo, Brazil

Renata Cristina Gasparino

2 School of Nursing, University of Campinas, Campinas, São Paulo, Brazil

Ana Claudia Puggina

3 Post-graduate Program in Nursing, Guarulhos University, Guarulhos, São Paulo, Brazil

Associated Data

All relevant data are within the paper.

1) To identify the patient’s perception of invasion of territorial and personal space and 2) to evaluate whether personal characteristics, housing conditions and characteristics of the hospital unit affect this perception.

Analytical, cross-sectional and quantitative study. An adapted version of the “Anxiety Due to Territory and Space Intrusion Questionnaire” was applied with patients hospitalized in the internal medicine and maternity wards and in the ward for patients with private health insurance of a university hospital in the state of São Paulo.

The sample consisted of 300 patients. The mean total score of the questionnaire administered was 143.58 (SD = 18.88). The mean subscale scores for territorial space and personal space invasion were 89.10 (SD = 15.29) and 54.48 (SD = 10.58), respectively. The invasion of territorial space differed significantly between patients with and without children (p = 0.02) and for the number of people living in the residence (p < 0.01).

Conclusions

Attitudes of the nursing staff, such as touching the patient’s possessions without permission and exposing the patient, caused discomfort and violated patient privacy. Patients who were lonelier and had more privacy at home perceived greater invasion of their territorial space by the nursing professionals.

Introduction

The social meaning of space, i.e., how humans consciously or unconsciously structure their own space and its influences on interpersonal relationships, is studied by proxemics [ 1 ], which defines three types of space: fixed feature space (e.g., walls), semi-fixed feature space (e.g., arrangement of furniture, obstacles and decoration), and informal space (e.g., personal territory around an individual’s body) [ 1 – 2 ]. With respect to informal features, every human being have a private space around himself/herself, the size of which depends on the population density of the place where he/she was raised. The space of a person is therefore culturally determined [ 3 ] and, regardless of how much a person tries, it is impossible to disregard his/her culture as this determines how an individual perceives the world [ 2 ].

The personal space is divided into four distance zones: intimate, personal, social, and public. The distance chosen depends on the relationship between individuals, how they feel, and what they are doing [ 2 ]. The intimate zone is reserved for affectively close people that have permission to approach and is the most important for healthcare providers. In the hospital setting, most procedures and interventions are performed at this distance, often without the due affectivity and permission [ 2 – 3 ]. Within this context of the cultural and personal use of space, healthcare providers need to know and respect the limits of the physical distance that should be maintained in different situations of interaction with the patient so that both feel comfortable [ 1 ].

By caring for the patient, nurses touch the body and expose it, often without asking permission, adopting an attitude of “power” over the body of the other. Being naked can mean discomfort and embarrassment, feelings demonstrated by expressions of surprise, shame, fear, and nervousness [ 4 ]. In the hospital setting, the patient shares his/her space with strangers, other patients and healthcare workers. Consequently, the feeling of space invasion occurs more frequently than in the family environment, since the individuals usually experiences situations of reduced privacy and control over their bodies and the area that surrounds them [ 5 ].

Territoriality is the area that individuals claim as their own, defending it from other members of the same species. There are three ways to invade the territory of the patient, invasion by looking, actual invasion when somebody touches the patient’s possessions without permission, and invasion with objects of both the patient's body and the space it occupies [ 1 ].

A study conducted in Nepal to evaluate patients’ attitudes towards physical privacy and confidentiality of information during consultation in a public hospital showed that the majority of patients were not comfortable having other patients in the same room. The authors suggest that attention should be given to reorganizing outpatient facilities and that future facilities should provide more privacy [ 6 ]. Another international study reported a strategy for working with the issue of patient privacy and satisfaction with healthcare providers and concluded that continued training and education are essential so that healthcare workers remain aware of these issues. The intervention strategies developed to improve patient privacy and satisfaction included the reorganization of the physical space, process management, access control, staff education and training, as well as ethical aspects [ 7 ].

The issue in question has an important dimension in the care and should be considered a professional ethical principle. Authors have demonstrated that the violation of personal (staff behavior) and territorial (hospital environment) privacy can threaten the dignity of patients and be misinterpreted by patients, causing constraints or inducing defensive behaviors [ 8 – 9 ], therefore the avoidance of this should be guaranteed by the nursing staff [ 10 ]. Accordingly, to ensure clear communication that allows the patient to control decision making [ 8 , 11 ], as well as providing respect, privacy and confidentiality of data are fundamental strategies for the maintenance of the dignity of the patients [ 11 ].

The fact that neither the actual invasion nor the perception of invasion is always clearly perceived by healthcare providers or the patient highlights the importance of this study for increasing the awareness of the nursing staff regarding the comprehension of the feelings experienced by patients when their space is invaded. Therefore, the aims of this study were to identify the patient’s perception of invasion of territorial and personal space and to determine whether personal characteristics, housing conditions and characteristics of the hospital unit have an impact on this perception.

A cross-sectional, analytical and quantitative study was conducted at a public hospital in the interior of the state of São Paulo, in the internal medicine and maternity wards and in the ward for patients with private health insurance. The internal medicine ward has 22 beds and mainly attends patients undergoing minor surgeries in the hospital. The ward comprises 5 rooms with 2 beds and 2 rooms with 6 beds sharing the same physical space. The maternity ward has 34 beds and attends pregnant and postpartum women and newborns, having 11 rooms with 2 beds and 3 rooms with 6 beds. The ward for private patients has 16 beds divided into 8 rooms with 2 beds each.

The criteria for inclusion in the study were to be aged 18 to 60 years, hospitalized for more than 24 hours and literate. The minimum sample size was calculated, using the calculator available at the website of the Laboratório de Epidemiologia e Estatística , Instituto Dante Pazzanese de Cardiologia , for a pilot sample of 30 participants. Standard deviation (σ = 30.08) and mean (μ = 126.17) were used to calculate the coefficient of variation (CV = σ/μ; CV = 0.238) and maximum error of the estimate (MEE = CVxσ; MEE = 7.17). The level of significance was pre-established at 5% and the minimum sample size estimated for application of the instrument was 68.

The questionnaire for the characterization of the participants consisted of 12 variables: personal characteristics (gender, age, marital status, education level, and having children), hospital unit (whether or not the patient shared a room in the hospital), and housing conditions (whether or not the patient shared a room, number of people with whom the patient shared the room in their house, which people shared the room, having a personal space at home, number of rooms in the patient’ house, and number of household members).

The Anxiety Due to Territory and Space Intrusion Questionnaire used was designed to identify the feelings of hospitalized patients regarding invasion of their personal and territorial space. The validation study and the cross-cultural adaptation to the Brazilian reality of Anxiety Due to Territory and Space Intrusion Questionnaire was published in 1998 and obtained satisfactory psychometric qualities [ 5 ].

The questionnaire consists of 33 questions divided into two subscales, with 19 items in the territorial space invasion subscale and 14 items in the personal space invasion subscale. The response alternatives for each item are measured on a Likert-type scale from 1 (totally unpleasant) to 7 (extremely pleasant), with the total score ranging from 33 to 231. With higher scores indicating greater perception of personal and territorial space invasion [ 5 ].

The patients were approached in the hospital and the data collected between January and March 2015. The study was conducted in accordance with national and international ethical guidelines on research involving human subjects and was approved by the Research Ethics Committee of Faculty of Medicine Jundiaí (Authorization No. 859.952/2015).

The data were analyzed through descriptive and inferential analysis using the IBM Statistical Package for the Social Sciences (SPSS, version 20.0). Spearman’s correlation test was used to compare the numerical variables with the scores of the questionnaire. Categorical variables were compared with the scores using the Kruskal-Wallis and Mann-Whitney tests. The error probability adopted in the tests was p<0.05. A trend was considered significant when p≤0.10.

The sample was composed of 300 patients, with a mean age of 30.9 years (SD = 7.8). There was a predominance of women (n = 279; 93%), married subjects (n = 122; 40.7%), patients with complete high school education (n = 166; 55.5%), and patients who had children (n = 262; 87.3%). The majority of participants were hospitalized in the maternity ward in the rooms with six beds (n = 126; 42%) ( Table 1 ).

Regarding housing, the majority of participants shared their room (n = 253; 84.7%) with another person (n = 191; 63.7%), which was the spouse (n = 205; 68.3%) and reported not having any personal space in the house (n = 260; 86.7%). The majority of residences had four rooms in the house (n = 133; 44.3%) occupied by two people (n = 105; 35%) ( Table 1 ).

Table 2 shows the total mean score and subscale scores of the responses of the participants regarding invasion of their space. As can be seen in the table, the perception of invasion of territorial space was greater than that of personal space.

In the territorial space invasion subscale, the three highest means were observed for items 9 (μ = 5.07; SD = 1.38), 5 (μ = 4.86; SD = 1.24) and 10 (μ = 4.85; SD = 1.21). In these the participants reported that touching their personal possessions without permission, changing the bedside table to a position that cannot be reached, and raising or lowering the window blinds without consulting the patient were attitudes of the nursing staff that annoyed them and caused a feeling of invasion ( Table 3 ).

In the personal space invasion subscale, the three highest means were found for items 13 (μ = 6.17; SD = 1.20) and 12 (μ = 6,13; SD = 1.21). These showed that embarrassing attitudes occur when the nursing staff conduct a technical procedure in an intimate area or change the patient's clothes without a screen ( Table 3 ).

Table 4 shows the comparison of invasion of territorial and personal space with the other variables studied. The statistically significant differences indicate that patients who no had children (p = 0.02) and those living with only one people in the residence (p < 0.01) perceived greater invasion of their territorial space. The significant trends indicate that patients who shared the room (p = 0.09) or were hospitalized in the maternity ward (p = 0.10) felt less personal space invasion.

Kruskal-Wallis Test/ *Mann-Whitney Test.

SD: Standard deviation.

The correlations between age and Invasion of territorial space (p = 0.14) and Invasion of personal space (p = 0.50) were not statistically significant.

The greater perception of territorial invasion is probably due to the fact that patients are somehow prepared for personal invasion in the hospital as they are aware that the approximation by unknown people to perform procedures and to touch their body is part of the treatment. However, territorial invasion is less tolerated since the instinctive drive is stronger, directing the control to personal possessions. Territorial invasion could have been unconsciously interpreted by the patients as a threat due to their vulnerable and dependent condition. In fact, other authors [ 9 ] have reached a similar conclusion regarding the more frequent occurrence of work activities in the patients’ room.

International studies [ 6 – 7 ] have demonstrated the same problems of invasion by healthcare providers as those raised in Brazilian studies and in the present one. Touching the patient’s possessions without permission, changing the bed side table to a position that cannot be reached, and raising or lowering the window blinds without consulting the patient are attitudes of the nursing staff that cause much discomfort. Healthcare providers need to be more attentive to the patient’s space and respect the territoriality established by them, often with their personal objects and possessions. Small actions, such as changing the place of the cell phone or slippers, can symbolize the removal of territory and generate strong feelings of discomfort [ 1 ].

Physical exposure of the patient is another factor that needs to be highlighted. Performing a technical procedure in an intimate area and changing the patient’s clothes without a screen are actions that cannot be accepted and that must be constantly supervised and addressed by the team, as privacy is a necessity and right of every human being and is essential to the maintenance of dignity. Embarrassment due to exposure of the body, lack of intimacy and disrespectful behavior by nursing professionals has also been reported by patients in other studies [ 12 – 13 ].

In a study with 40 patients, using the same scale, three of the four situations identified by the authors that received the highest mean scores were the same as those of the present study and were even scored higher by the patients: “the nursing staff touch the patient’s possessions in the drawer without his/her permission”, “the nursing staff change the patient’s clothes without closing the screen”, and “the nursing staff perform a technical procedure in an intimate area without closing the screen” [ 12 ].

Embarrassment of the patient in the hospital environment is generally caused by exposure of the body to other patients, relatives and healthcare workers. Nudity in front of strangers can be deeply iatrogenic. Within this context, the age, gender and culture of the affected subjects can directly affect the communication dynamics. The results found corroborate studies in the literature in which the authors observed discomfort of the patient with nudity and body exposure and manipulation [ 6 – 7 , 14 – 15 ]. The patients reported that requesting permission to manipulate their body, to examine them or to perform other care/procedure shows consideration and attention on the part of the professional, which makes the patient feel valued and in control of the situation. This approach may minimize the effects of the invasion and the feeling of being seen as an object [ 14 ].

The respect of territory and personal space represents an ethical and respectful approach to patients, which can permit to maintain their dignity even under vulnerable conditions, favouring their recovery, as most studies have highlighted [ 7 – 11 ].

The results of the present study are in line with those of other national and international studies, which have investigated similar problems concerning patients’ perception of invasion of their territory and personal space by heath care providers [ 6 – 8 , 10 – 11 ]. Other authors [ 15 ] suggest that unnecessary actions and exposure responsible for discomfort of patient should be avoided, because potentially detrimental to individual dignity and treatment results.

The limitations of this study that can be mentioned include the non-random selection of the participants, the fact that it was performed in only one public hospital in Brazil, which serves predominantly the maternal and child public and, consequently, the significant number of female participants, unbalancing the sample with respect to gender. Other limitations need be reported. The cross-sectional nature of our study can only provide associations, the study evaluated only self-reported perceptions of patients and not actual practice by healthcare staff and the sample is not representative of other settings in the country.

Further studies involving other health professionals and institutions, with sizes and characteristics different to the study hospital, should be carried out with the purpose of sensitizing and identifying what actions are being implemented in order to guarantee the privacy, autonomy and information required to guarantee the dignity of patients.

The patients felt their space invaded in the hospital environment; with this perception of invasion being greater regarding the territorial space than the personal space.

The findings of this study, by self-reported perception of patients, showed that the attitudes of the nursing staff, such as touching the patient’s possessions without permission and exposing the patient, caused discomfort and violated patient privacy. Patients who were lonelier and had more privacy at home perceived greater invasion of their territorial space by nursing professionals.

Healthcare should respect the individuality and dignity of the patient, not only including changes in the physical space, but also in the actions and behavior of healthcare providers regarding patient privacy.

Funding Statement

The authors received no specific funding for this work.

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