Perry et al. 2015 (Personal Space)

Perry et al. (2015) is a double-blind experiment showing that oxytocin changes how close people want others to stand, depending on their empathy. It drew highly empathic men closer and tended to push less empathic men away. The study challenges the idea that oxytocin is simply a “love hormone.”

Psychology Being Investigated

1. Interpersonal Distance (Personal Space)

Interpersonal distance, or personal space, is the physical space people prefer to maintain between themselves and others.

This preferred distance varies based on relationships, cultural norms, and personal factors. When someone enters another person’s personal space, it can cause discomfort or even feelings of threat.

Hall (1966) proposed four zones of interpersonal distance:

• Intimate distance: used for close family members or intimate partners.
• Personal distance: used for everyday interactions.
• Social distance: used for formal interactions.
• Public distance: used for public figures such as lecturers.

Preferred distance is not fixed. Reviews of decades of research find that it varies with sex, age, personality, relationship, emotional state and culture (Hayduk, 1983). People also actively defend and renegotiate their space, for example by rearranging chairs or choosing seats (Sommer, 1969).

2. Social Hormone: Oxytocin

Oxytocin, a social hormone that acts as a neurotransmitter, plays a significant role in social bonding, childbirth, and breastfeeding.

It generally promotes prosocial and approachable behaviors, though it may also lead to envy, risk aversion, or hostility towards strangers under certain conditions.

Rather than universally increasing prosocial behaviors, oxytocin (OT) appears to enhance the salience, or attention-grabbing nature, of social cues, including those related to interpersonal distance.

The effect depends on empathy and context. As a result, OT can lead to both increased and decreased interpersonal distance preferences.

3. Empathy and Social Behaviour

Empathy is a key trait in social relationships, reflecting a person’s ability to understand and share the feelings of others.

Empathy includes two aspects:

• Cognitive empathy: recognizing others’ emotions.
• Affective empathy: the ability to feel what another person feels.

Empathy influences how people interpret social cues and respond emotionally.

The fact that empathy influences our perception of interpersonal distance underscores its importance as a social signal.

Individuals with differing empathy levels might perceive and react to the same interpersonal distance in vastly different ways, shaping their social interactions accordingly.

For instance, someone high in empathy might be more attuned to subtle nonverbal cues of anxiety or discomfort in others, prompting them to adjust their preferred interpersonal distance accordingly.

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Background

Perry et al. explored the effects of oxytocin on people’s preferred interpersonal distances, focusing on differences between individuals with high versus low empathy levels.

The Amygdala and Personal Space

The amygdala is a critical component in regulating preferred interpersonal distance. This almond-shaped structure in the limbic system flags socially significant stimuli, especially potential threat.

Damage to the amygdala has been associated with a decreased need for personal space. Discomfort at close range tends to track higher amygdala activity.

Kennedy et al. (2009) studied a rare patient with complete bilateral amygdala damage. She had effectively no sense of personal space. She was comfortable standing far closer to strangers than other people would tolerate.

In healthy participants in the same work, the amygdala became active when another person was close by.

Oxytocin is known to affect the activity of the amygdala. Its receptors are dense in the amygdala and related circuits, which helps explain how it shifts social and emotional processing.

The Social Salience Hypothesis

Previous research often presented a simplistic view of oxytocin (OT) as a universally “pro-social” hormone. Early work reported that intranasal oxytocin increased trusting behaviour in an economic game, which fuelled its “trust hormone” label (Kosfeld et al., 2005).

Later studies told a different story (Bartz et al., 2011). Its effects depend on the person and the situation.

The Perry et al. (2015) study challenged this view by investigating the social salience hypothesis.

The social salience hypothesis suggests that oxytocin heightens the salience of social cues, meaning how strongly they grab attention (Shamay-Tsoory & Abu-Akel, 2016). This changes how individuals perceive and react to those cues in different social settings.

This means oxytocin doesn’t necessarily make everyone more pro-social. It amplifies existing social cues and their emotional relevance, leading to context-dependent effects on social behavior.

This hypothesis posits that oxytocin may lead one person to feel more at ease in a social setting while causing another to feel stressed.

Perry et al. aimed to test this hypothesis. They proposed that oxytocin could intensify one’s emotional response to social situations. If a person feels safe, this feeling might be amplified. If they feel threatened, the negative response may also be heightened.

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Aims

The Perry et al. study aimed to uncover the complex interplay between oxytocin, empathy, and social context in shaping interpersonal distance preferences.

The main aims were:

1. To determine if oxytocin affects preferred interpersonal distances.
2. To investigate whether empathy levels influence oxytocin’s effects on interpersonal distance preferences.
3. To explore these effects in different social contexts (e.g., with friends vs. strangers).

Understanding these aims is important because it can help explain how biological factors (hormones) interact with psychological traits (empathy) to influence social behavior.

This knowledge could have applications in treating social disorders or improving social interactions.

The researchers specifically hypothesized that:

• OT would decrease preferred interpersonal distances in individuals with high levels of empathy, but increase preferred interpersonal distances in individuals with low levels of empathy.
• OT’s effect on interpersonal distance would vary depending on the specific social situation, such as the type of person someone is interacting with (friend vs stranger).
• The effect would be specific to social situations and absent for non-social controls.

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Method

The study involved two experiments (counter-balanced order) with the same participants and experimental design.

Design

Mixed-model design:

• Within-subjects design (each participant completed both oxytocin and placebo conditions).
• Between-subjects design for the empathy group (high and low).

The study used a double-blind, placebo-controlled design. Neither the experimenter nor the participant knew whether the participant had received the OT or the placebo.

Participants attended the laboratory twice, exactly one week apart and at the same time of day, and completed both experiments in each session.

During their first visit, they were randomly assigned to self-administer either oxytocin (24 units in 250 ml of saline) or a placebo (250 ml of saline without oxytocin).

Three drops were administered to each nostril. On their second visit, participants self-administered the alternative solution.

At the first visit, participants completed the Interpersonal Reactivity Index (IRI) after receiving the spray. The IRI is a 28-item self-report questionnaire with four subscales: perspective taking, empathic concern, personal distress and fantasy (Davis, 1983).

Each participant belonged to only one empathy group (high or low). This part of the design therefore used independent measures.

They then waited for 45 minutes in a quiet room with nature magazines to allow oxytocin levels to stabilize before proceeding to the experiments.

The order of the experiments 1 & 2 was counterbalanced among the participants.

Sample

• 54 male undergraduate student volunteers at the University of Haifa.
• Convenience sampling method.
• Ages ranged from 19 to 32 years old, with a mean age of 25.29 years.
• They received course credit or payment for taking part.
• All participants had normal or corrected-to-normal vision and no history of psychiatric or neurological disorders.
• Five participants were left-handed.
• Participants were divided into high and low empathy groups based on their scores on the Interpersonal Reactivity Index (IRI).

Only 40 of the 54 men formed the analysis groups: 20 high-empathy and 20 low-empathy participants. They scored half a standard deviation above or below the mean IRI score (36.25).

The sample was all male. Local ethics rules restricted intranasal oxytocin in women, and earlier studies suggest it affects men and women differently (Perry et al., 2015).

Results: Experiment 1: CID

Main Effect of IV Condition(s):

Neither oxytocin nor empathy alone had a significant main effect on preferred distance.

The type of approaching figure significantly influenced participants’ preferred interpersonal distance.

Participants consistently preferred different distances for each protagonist. That held for both empathy groups and both treatments.

Preferred distance increased in this order: friend, ball, authority figure, stranger. This order likely reflects a gradient of perceived social threat, with the friend posing the least threat and the stranger the most. The authors did not measure perceived threat directly, so this remains an interpretation.

Two-Way Interaction Effect of Oxytocin (Treatment) and Empathy:

The effect of oxytocin on preferred interpersonal distance was not uniform across all participants but depended on their pre-existing empathy levels. This interaction only approached statistical significance (p = .09), and oxytocin’s effect was not significant within either group on its own (p > .1).

• High Empathy Group: Highly empathic individuals tended to prefer closer distances with oxytocin. In the high empathy group, oxytocin reduced the preferred mean distance from the protagonist (placebo: 26.11% vs. oxytocin: 23.29%).
• Low Empathy Group: In the low empathy group, oxytocin increased the preferred mean interpersonal distance (placebo: 26.98% vs. oxytocin: 30.20%). However, these differences were minimal.

Three-Way Interaction of Treatment, Condition, and Empathy:

The results revealed a significant three-way interaction between treatment (oxytocin vs. placebo), condition (type of protagonist), and empathy (high vs. low).

The effect was driven by the high empathy group. Their treatment-by-condition interaction was significant (p = .005), while the low empathy group’s was not (p = .18).

Within the high empathy group, the effect of oxytocin on preferred distance was most pronounced in the condition with the rolling ball. The reasons are not entirely clear.

Oxytocin might have a particularly potent influence on how people respond to social cues that are less overtly threatening or more ambiguous. The authors note that the ball is widely used as a non-social baseline. Its role needs further research.

In the high empathy group under placebo, preferred distances differed significantly between friend and authority figures, and between friend and stranger, as expected. However, no significant differences were noted between the ball and other conditions.

Oxytocin changed that pattern. Participants in the high empathy group were willing to be significantly closer to the ball than to the stranger or authority figure.

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Results: Experiment 2 (Choosing Rooms)

Main Effect of IV Condition(s):

There were no significant main effects of either “treatment” (oxytocin vs. placebo) or “empathy” (high vs. low) on preferred chair distance.

This means that, when considered in isolation, neither receiving oxytocin nor having high or low empathy significantly influenced how close or far participants wanted the chairs to be.

Preferred chair distance differed significantly from table-to-plant distance. This was expected. The two were set at different distances from the start, so it was not the focus of interest.

Two-Way Interaction Effect of Oxytocin (Treatment) and Empathy:

The interaction between oxytocin and empathy was statistically significant only for the “chairs” condition, the measure of interpersonal distance.

This means that oxytocin’s effects on preferred distance were specific to the social context of anticipated interaction with another person, represented by the two chairs.

Oxytocin and empathy did not interact to influence preferred distances in the control condition (table and plant).

Effect on Chair Distance:

• High empathy participants preferred closer chair distances in the oxytocin condition compared to the placebo condition (oxytocin: 78.07 cm vs. placebo: 80.58 cm). The effect of oxytocin on chair distance for the high empathy group approached statistical significance.
• Low empathy participants preferred greater chair distances under the oxytocin condition (oxytocin: 80.14 cm vs. placebo: 78.33 cm).

Effect on Chair Angle:

• Oxytocin had no effect on preferred chair angle for either high or low empathy groups.

Three-Way Interaction of Treatment, Condition, and Empathy:

The most important finding was a significant three-way interaction between “condition,” “treatment,” and “empathy.”

This complex interaction suggests that oxytocin’s effect on preferred distance varied with both the condition (chairs vs. tables) and the participant’s empathy level.

The two tasks measured related but slightly different constructs. Preferred distance in the CID task under placebo correlated moderately with chair distance in the room task (r = .278, p < .05).

Despite their different demands, the two tasks produced strikingly similar effects of oxytocin. The authors took this replication as evidence of a true effect.

Conclusions

1. Oxytocin influences preferred interpersonal distance based on empathy levels.
2. Highly empathic participants preferred closer interpersonal distances when given oxytocin.
3. Low empathy participants preferred greater distances when given oxytocin.
4. These effects are specific to interpersonal contexts and don’t apply to non-social spatial preferences.
5. The findings support the “social salience hypothesis,” which suggests oxytocin enhances the perception of social cues, leading to different outcomes based on individual traits and context.
6. The researchers suggested that oxytocin may promote closeness in highly empathetic individuals, especially during non-threatening interactions.
7. This is supported by the finding that oxytocin’s effect was more pronounced when participants interacted with the ball than with a stranger or authority figure.

Why would one dose have opposite effects? According to the social salience account, oxytocin sharpens attention to social cues, and the outcome depends on how a person reads them. For someone who finds social approach rewarding, heightened salience invites closeness. For someone who finds it uncomfortable, it prompts avoidance.

Strengths of the Study

The study’s main strengths lie in its design, its controls and its measurement:

• Double-Blind, Placebo-Controlled Design: This double-blind design is the gold standard in clinical research. Because nobody knew who received oxytocin, it limits expectation and experimenter effects and strengthens the causal link to preferred distance.
• Random Allocation: Participants were randomly assigned to receive either oxytocin or the placebo. This random allocation strengthens internal validity, because observed effects are more likely due to oxytocin than to pre-existing differences.
• Two Sessions, One Week Apart: The gap limits carryover, so oxytocin from the first session had worn off by the second. It also allowed a within-subjects design: each participant served as their own control, which boosts statistical power.
• Replication Across Experiments: Two experiments using different paradigms produced similar patterns: oxytocin promoted closer distances in highly empathic individuals and greater distances in those low in empathy. This strengthens the reliability of the findings.
• Non-Social Control: The table-and-plant spacing in Experiment 2 acted as a non-social control. Oxytocin did not alter it, so the effect was specific to social contexts.
• Objective, Standardized Measurement: Computerized presentation and standardized procedures gave objective, quantitative measures of distance and angle and reduced subjective bias. The CID paradigm is an established, validated measure.

Weaknesses of the Study

The main weaknesses concern the sample, the tasks, the statistics and the ethics:

• Low Generalizability: The sample was all male undergraduates from one Israeli university, mostly right-handed. Oxytocin’s effects and personal-space norms both differ by sex and culture, so the findings may not generalize to women or other cultures.
• Low Ecological Validity: Both experiments used computerized tasks, which may not reflect real-world interactions. The authors report, however, that such preferences correlate strongly with a live stop-distance measure, which partly offsets the concern.
• Hypothetical Intimacy Context: In Experiment 2, participants were told they would later have an intimate conversation, but it never happened. Their room choices may not reflect genuine preferences in real self-disclosure.
• Marginal Statistics: In Experiment 1, the key treatment-by-empathy interaction only approached significance (p = .09). Clearer results emerged only in complex three-way interactions, which the authors acknowledge are harder to interpret.
• Small Groups: Each empathy group contained only 20 men, so effects that appear in complex interactions rest on small numbers.
• Demand Characteristics: Demand characteristics are cues that let participants guess a study’s purpose. Completing an empathy questionnaire and obvious distance tasks may have revealed the aim, though the double-blind design limits bias in the drug comparison.
• Ethics (Deception): In Experiment 2, participants were misled about a conversation that never took place. Deception limits fully informed consent, so it needs careful debriefing and justification.
• Ethics (Potential for Harm): Participants were told the study’s true purpose at the end of the two weeks. Even so, discovering the deception could leave some feeling embarrassed or distrustful of research.
• Ethics (Consent): Participation must be voluntary and based on informed consent. Student participants need genuine alternatives for earning course credit, so that their decision is not unduly influenced.

Contemporary Research

Research since 2015 asks whether the study’s limits, a small all-male sample and screen-based tasks, explain its result.

Immersive virtual reality (VR) offers a test, pairing a lifelike approaching figure with precise, computer-logged distances. Riem et al. (2019) ran one.

Riem et al. echo the central lesson: oxytocin’s effect on distance is conditional, not universal. Two moderators, adult empathy and childhood love withdrawal, now point the same way.

The VR study also narrows a limitation. It tested only women, where Perry et al. tested only men. Whether the two moderators act jointly in one mixed-sex sample remains open.

Issues and Debates

Application to everyday life: Healthcare Settings

• Patient-Provider Communication: Healthcare professionals can tailor their approach to build rapport. Noticing cues about a patient’s comfort with physical proximity lets providers adjust their positioning and communication style.
• Personalizing Treatment: Understanding how oxytocin and empathy interact could support more personalized approaches for patients with social anxieties. Tailoring interventions to empathy levels and likely triggers could improve therapeutic benefit.
• Cautious Use: The same dose that eases closeness for an empathic person could make a less empathic person more avoidant. The authors warn that oxytocin may strengthen initial social biases rather than improve social behavior.

Application to everyday life: Conflict Resolution

• Improving Mediation and Negotiation: Insights from the study can be valuable in conflict resolution contexts, such as mediation or negotiation settings.
  
  By considering individual differences in empathy and how these might influence responses to social cues, mediators can create more effective strategies for fostering understanding and collaboration between parties in conflict.
  
  For instance, recognizing that individuals with lower empathy traits might prefer greater physical distance during tense interactions could inform the mediator’s approach to facilitating dialogue and finding common ground.

Application to everyday life: Design and Public Space

Preferred distance is a real, measurable quantity that varies between individuals, so it matters wherever people share space:

• Architecture and Seating: Sommer (1969) treated personal space as a design variable. Because comfortable spacing varies systematically between people, there is no single correct distance for waiting rooms, clinics, classrooms or care settings.
• Flexible Layouts: Flexible seating and movable chairs let individuals choose and adjust their own distance. This accommodates differences better than a fixed layout.
• Crowding and Queues: Linking preferred distance to empathy and to oxytocin-sensitive, amygdala-based processing may help explain why some people find crowds, queues or lifts far more aversive than others.
• Public Health: Distancing during disease outbreaks and the design of shared public space use default distances that will suit some people far better than others.

Individual and situational explanations

Perry et al. (2015) provide compelling evidence that neither individual traits nor situational variables alone can fully explain complex social behaviors like interpersonal distance preferences.

Instead, behavior emerges from the dynamic interaction between individual traits (such as empathy) and situational factors (such as oxytocin and the type of approaching figure).

It shows that oxytocin’s effects on personal space preferences vary based on individual empathy levels and contextual cues.

Alternative Explanations of Personal Space

Perry et al. explain the opposite effects through the social salience hypothesis. Two older accounts help show what that adds.

Equilibrium theory (Argyle & Dean, 1965) treats distance as one channel in a self-regulating system for managing intimacy. If someone stands too close, a person compensates on another channel, such as eye contact or body orientation.

It predicts that distance shifts when intimacy is disturbed. It cannot say why the direction of the shift would depend on a stable trait like empathy.

The result is hard for it to explain.

A purely amygdala-based account (Kennedy et al., 2009) says one threat-detection circuit regulates distance. Oxytocin’s dense receptors in the amygdala would then act like a volume dial, shifting distance the same way for everyone.

That cannot explain why one dose lengthens distance in low-empathy participants while shortening it in high-empathy participants. It predicts a difference of degree, not a reversal.

The social salience account keeps the amygdala’s role as a proximity monitor. It adds that oxytocin changes how salient the monitored social signal is, not just how alarming it is. That allows a genuine reversal of direction.

The findings therefore do not replace the older accounts. Distance regulation probably still runs through an intimacy system and an amygdala-based threat circuit. Trait empathy decides which way it moves a person.

Nature versus nurture

The study touches on this debate by examining how a biological factor (oxytocin) interacts with a psychological trait (empathy) that may be influenced by both genetics and environment.

This supports an interactionist perspective on the nature-nurture debate.

Oxytocin did not push everyone in one direction. Its effect was expressed only through each person’s social disposition, which is itself partly learned. Neither the hormone nor empathy alone changed preferred distance on average. Only together did they predict a shift.

Reductionism versus holism

• The focus on a single hormone and its effects on a specific behavior represents a reductionist element.
• Instead, the study leans towards a more holistic perspective by acknowledging the influence of multiple factors on human behavior, such as empathy and contextual factors.

The design could be caricatured as biologically reductionist, because it reduces personal space to a single hormone. The study argues the opposite.

Oxytocin’s effect depended on a psychological trait (empathy) and on the social context, which supports an interactionist account in which biology and individual psychology jointly shape behavior.

References

Argyle, M., & Dean, J. (1965). Eye-contact, distance and affiliation. Sociometry, 28(3), 289–304. https://doi.org/10.2307/2786027

Bartz, J. A., Zaki, J., Bolger, N., & Ochsner, K. N. (2011). Social effects of oxytocin in humans: Context and person matter. Trends in Cognitive Sciences, 15(7), 301–309. https://doi.org/10.1016/j.tics.2011.05.002

Davis, M. H. (1983). Measuring individual differences in empathy: Evidence for a multidimensional approach. Journal of Personality and Social Psychology, 44(1), 113–126. https://doi.org/10.1037/0022-3514.44.1.113

Hall, E. T. (1966). The hidden dimension. Doubleday.

Hayduk, L. A. (1983). Personal space: Where we now stand. Psychological Bulletin, 94(2), 293–335. https://doi.org/10.1037/0033-2909.94.2.293

Kennedy, D. P., Gläscher, J., Tyszka, J. M., & Adolphs, R. (2009). Personal space regulation by the human amygdala. Nature Neuroscience, 12(10), 1226–1227. https://doi.org/10.1038/nn.2381

Kosfeld, M., Heinrichs, M., Zak, P. J., Fischbacher, U., & Fehr, E. (2005). Oxytocin increases trust in humans. Nature, 435(7042), 673–676. https://doi.org/10.1038/nature03701

Perry, A., Mankuta, D., & Shamay-Tsoory, S. G. (2015). OT promotes closer interpersonal distance among highly empathic individuals. Social Cognitive and Affective Neuroscience, 10(1), 3–9.

Riem, M. M. E., Kunst, L. E., Steenbakkers, F. D. F., Kir, M., Sluijtman, A., Karreman, A., & Bekker, M. H. J. (2019). Oxytocin reduces interpersonal distance: Examining moderating effects of childrearing experiences and interpersonal context in virtual reality. Psychoneuroendocrinology, 108, 102–109. https://doi.org/10.1016/j.psyneuen.2019.06.012

Shamay-Tsoory, S. G., & Abu-Akel, A. (2016). The social salience hypothesis of oxytocin. Biological Psychiatry, 79(3), 194–202. https://doi.org/10.1016/j.biopsych.2015.07.020

Sommer, R. (1969). Personal space: The behavioral basis of design. Prentice-Hall.

Keep Learning

To help reinforce your understanding and prepare for potential exam questions, here are some practice questions related to this study for AICE Psychology:

1. Describe the main aims of the study by Perry et al. on oxytocin and interpersonal distance. (4 marks)
2. Explain two ethical issues raised by this study and how researchers might address them. (6 marks)
3. Evaluate the strengths and weaknesses of using a computerized task to measure interpersonal distance preferences. (8 marks)
4. Discuss how this study relates to the nature-nurture debate in psychology. (6 marks)
5. Explain how the researchers controlled for individual differences in this study. Why is this important? (6 marks)
6. How does this study demonstrate the interaction between biological and psychological factors in influencing behavior? (8 marks)
7. Describe the main findings of Experiment 1 (CID task) and explain what they suggest about oxytocin’s effects on social behavior. (6 marks)
8. Evaluate the generalizability of this study’s findings. Consider both strengths and limitations. (8 marks)
9. How does this study contribute to our understanding of individual differences in social behavior? (6 marks)
10. Describe one way in which the findings from this study could be applied to real-world situations or treatments. What ethical considerations would need to be taken into account? (8 marks)

Remember to use specific details from the study when answering these questions. Practice structuring your responses clearly, using psychological terminology correctly, and balancing description with evaluation where required.

Study Summary Sheet

Original Journal Article