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British Journal of Psychology (2015), 106, 107–132 © 2014 The British Psychological Society www.wileyonlinelibrary.com

Reach out to one and you reach out to many: Social touch affects third-party observers Annett Schirmer1,2,3*, Christy Reece1, Claris Zhao1, Erik Ng1, Esther Wu1,4,5 and Shih-Cheng Yen3,4,5 1

Department of Psychology, National University of Singapore, Singapore Duke/NUS Graduate Medical School, Singapore 3 LSI Neurobiology/Ageing Programme, National University of Singapore, Singapore 4 Department of Electrical and Computer Engineering, National University of Singapore, Singapore 5 Singapore Institute for Neurotechnology, National University of Singapore, Singapore 2

Casual social touch influences emotional perceptions, attitudes, and behaviours of interaction partners. We asked whether these influences extend to third-party observers. To this end, we developed the Social Touch Picture Set comprising line drawings of dyadic interactions, half of which entailed publicly acceptable casual touch and half of which served as no-touch controls. In Experiment 1, participants provided basic image norms by rating how frequently they observed a displayed touch gesture in everyday life and how comfortable they were observing it. Results implied that some touch gestures were observed more frequently and with greater comfort than others (e.g., handshake vs. hug). All gestures, however, obtained rating scores suitable for inclusion in Experiments 2 and 3. In Experiment 2, participants rated perceived valence, arousal, and likeability of randomly presented touch and no-touch images without being explicitly informed about touch. Image characters seemed more positive, aroused, and likeable when they touched as compared to when they did not touch. Image characters seemed more negative and aroused, but were equally likeable, when they received touch as compared to when there was no physical contact. In Experiment 3, participants passively viewed touch and no-touch images while their eye movements were recorded. Differential gazing at touch as compared to no-touch images emerged within the first 500 ms following image exposure and was largely restricted to the characters’ upper body. Gazing at the touching body parts (e.g., hands) was minimal and largely unaffected by touch, suggesting that touch processing occurred outside the focus of visual attention. Together, these findings establish touch as an important visual cue and provide novel insights into how this cue modulates socio-emotional processing in third-party observers.

Navigating one’s social environment is challenging. There are multiple relationships and social groups each characterized by a number of factors including their specific purpose (e.g., professional vs. private), intimacy (e.g., friend vs. acquaintance), and behavioural norms (e.g., child vs. adult). To complicate matters further, these factors are not fixed but

*Correspondence should be addressed to Annett Schirmer, Department of Psychology, Faculty of Arts and Social Sciences, National University of Singapore, 9 Arts Link, Block AS4, Level 2, Singapore 117570 (email: [email protected]). DOI:10.1111/bjop.12068

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change dynamically as time goes by. Thus, in order to interact successfully, it is necessary to continuously update one’s social knowledge and the nature of one’s social ties. Here, we asked to what extent such updating results not only from one’s own social experiences but from the social experiences of others. More specifically, we were interested in the casual tactile exchanges that form part of non-intimate public interactions and sought to determine whether and how these exchanges affect third-party observers. It is well established that interpersonal touch shapes emerging relational styles. In a seminal study, Fisher, Rytting, and Heslin (1976) shed light on this by examining students who came to the university library to pick up their library cards. The library personnel, instructed by the researchers, either briefly touched the students when handing out their cards or handed their cards without touch. Subsequently, the researchers interviewed the students and found that those who were touched reported a more positive affect and evaluated the library and its personnel more favourably than those who were not touched. These findings have been replicated across other scenarios (Burgoon, Walther, & Baesler, 1992) and extended to reveal an impact of touching on brain activity and behaviour. Looking at brain activity, it was shown that touching enhances a person’s attention to concurrently presented emotional images (Schirmer et al., 2011). Looking at behaviour, Crusco and Wetzel (1984) reported that waitresses received larger tips from customers whom they touched briefly while serving than from customers whom they did not touch. Gu
eguen and Fischer-Lokou (2003) found that pleas for a free bus ride were more successful when they were accompanied by a brief touch than when they were made without touch. Lastly, in the context of health care it was shown that patients who were touched when asked to take a particular medicine reported greater compliance than patients who were not touched (Gu
eguen & Vion, 2009). Given the robustness of these social touch effects (for a review, see Schirmer, Wijaya, & Liu, accepted for publication), one may ask whether they extend to situations in which individuals are not personally touched, but perceive touch vicariously through mere observation. Such an extension seems viable because individuals are known to embody others’ somatosensory experiences, both painful and innocuous ones. In the context of painful experiences, researchers have shown that seeing someone else in pain elicits pain-related neural activity in the observer (Cheng et al., 2007; Jackson, Rainville, & Decety, 2006). Additionally, it increases sensitivity to a current painful stimulation of the observer’s body (Godinho et al., 2012). Work examining the observation of innocuous touch complements these results (Kuehn, Trampel, Mueller, Turner, & Sch€ utz-Bosbach, 2012; Pihko, Nangini, Jousm€aki, & Hari, 2010). In a study by Serino, Pizzoferrato, and Ladavas (2008), participants received a tactile stimulus to either the left side of their face, the right side of their face, or both sides. The participants’ task was to indicate where they had been stimulated. Concurrent with this task, they saw movies containing one of the following central objects: their own face, another person’s face, or a house. In these movies, hands were shown passing the central object with fingers either touching or not touching the object. Participants detected the tactile stimulus to their own face more accurately when watching touch as compared to no-touch movies of themselves. A smaller but similar effect emerged for movies with strangers but not for movies with houses. These findings were recently replicated and extended (Cardini, Tajadura-Jim
enez, Serino, & Tsakiris, 2013; Cardini et al., 2010). Among others, it was shown that innocuous touch embodiment involves brain regions associated with motor and somatosensory perception (Cardini et al., 2010). While much research examined vicarious touch, only a few studies explored its relation to socio-emotional processing. One such study by Banissy et al. (2011) focused

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on mirror-touch synaesthesia. Individuals who report this phenomenon perceive vicarious touch as actual touch, suggesting that they take ordinary tactile embodiment to its extreme. Interestingly, individuals with mirror-touch synaesthesia are better than control individuals at recognizing facial emotional expressions, suggesting that vicarious touch is relevant for socio-emotional processing (Banissy et al., 2011). Further evidence in line with this comes from an investigation of patients with hereditary sensory and autonomic neuropathy type V. Compared to healthy controls, these patients have fewer of the tactile receptors implicated in social touch. Consequently, they perceive social touch as less pleasant when they themselves are the tactile target (Olausson et al., 2002). Importantly, this also holds when they observe social touch to someone else (Morrison et al., 2011). Lastly, two rating studies explored how vicarious touch influences socio-emotional processing in healthy third-party observers (Major & Heslin, 1982; Summerhayes & Suchner, 1978). Most relevant for the present purpose is the work by Major and Heslin (1982) using sixteen silhouette images of dyadic interactions. In half of the images, the left individual touched the right individual on the shoulder. In the remaining images, there was no touch. Participants saw touch and no-touch images in separate blocks and rated either the left or the right individual with respect to status/dominance, instrumentality/ assertiveness, warmth/expressiveness, and attractiveness. Rating scores on the first three scales were higher for left individuals in touch as compared to no-touch images. In contrast, they were lower for right individuals in touch as compared to no-touch images. The authors concluded that touchers but not touch recipients benefit in the esteem of third-party observers. Taken together, existing work shows that touchers affect touch recipients both at a sensory and at a socio-emotional level. Touchers bias others to perceive them more positively and to behave more prosocially towards them (Crusco & Wetzel, 1984; Fisher et al., 1976). Importantly, there is ample evidence that third-party observers mirror aspects of the touch recipients’ experience. However, so far this evidence speaks primarily to the somatosensory aspects of touch (Cardini et al., 2010, 2013; Cheng et al., 2007; Jackson et al., 2006). Moreover, although a few studies explored the socioemotional consequences of vicarious touch (Banissy et al., 2011; Major & Heslin, 1982; Morrison et al., 2011), insights remain limited. Some such insights derive from special populations, such as those with mirror-touch synaesthesia or neuropathy. Therefore, they cannot be easily generalized to healthy populations. Other insights derive from normal populations but are methodologically weak in that only one touch gesture was explored, in that touch and no-touch images potentially differed in more than just touch, and/or that touch was confounded with image location (Major & Heslin, 1982; Summerhayes & Suchner, 1978). We sought to address these issues and to extend previous work on vicarious touch. To this end, we developed a set of line drawings called the Social Touch Picture Set (SToPS) showing 120 touch and no-touch interactions between two individuals. Advancing previous efforts, we included 10 different tactile gestures some of which were reciprocal and others of which were non-reciprocal. Additionally, care was taken to approximate touch and no-touch control images with respect to interpersonal distance, body posture, and hand position such that processing differences would arise from touch rather than from extraneous variables that vary with touch. Lastly, we presented each interaction in its original and mirrored form to exclude potential effects of image location. Here, we report three experiments exploring observer responses to SToPS images.

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The first experiment served to develop norms regarding the frequency at which displayed tactile interactions are encountered in real life. Additionally, it helped determine the comfort or discomfort participants experience observing these interactions. Although tactile exchanges are ubiquitous, some forms of touch are more frequent and acceptable for public use than others and we sought to ascertain such acceptability for our stimulus set. The second experiment was conducted to assess socio-emotional evaluations of and attitudes towards the SToPS images as a function of whether these images entailed touch. Lastly, we conducted an eye-tracking experiment in which participants passively viewed touch and no-touch images. This served to characterize how people naturally gaze at interpersonal interactions and to determine whether and how their gaze patterns are influenced by the presence of touch.

EXPERIMENT 1 Interpersonal touch can be used in a myriad of ways and with a myriad of effects. Apart from the fact that different tactile actions (e.g., stroking, slapping) convey different emotional meanings (Hertenstein, Keltner, App, Bulleit, & Jaskolka, 2006), the body parts involved further qualify touch. Depending on the relationship between toucher and touch recipient, as well as the context in which touch occurs, some body parts are more appropriate for touch than others and may elicit different kinds of bodily sensations, emotions, and social responses. For example, in a public environment where individuals feel prone to social judgment, being touched in intimate body parts (e.g., face, breasts) is likely to be arousing and negative, even if the toucher is a loved one. However, being touched on more public body parts (e.g., hand, arm) may potentially be calming and positive (Heslin, Nguyen, & Nguyen, 1983). Given our interest in the vicarious experiences of social touch, the contextual appropriateness of touch is important. Expecting positive socio-emotional effects from observing touch may be reasonable only if the observed touch represents a typical tactile interaction, which individuals encounter in public settings and which they are fairly comfortable observing. Experiment 1 served to ensure that this is the case for the type of interactions used in SToPS.

Methods Participants Two hundred and twenty-one undergraduate students participated in this research. The data of five participants were excluded from statistical analysis because they either failed to follow instructions (N = 2) or encountered a technical error (N = 3). The remaining 216 participants comprised equal numbers of males and females. Male participants were on average 22.09 (SD = 2.32) years old and female participants were on average 21.19 (SD = 2.68) years old.

Images Images were taken from the SToPS (for image access please visit https://dl.dropboxusercontent.com/u/24234612/SToPS_PNGFormat.zip or contact the corresponding author). They consisted of black line drawings on white background depicting six

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distinct, non-reciprocal casual touch gestures between two people as well as four reciprocal gestures (Table 1, Figure 1). The present authors selected these gestures based on their subjective assessment of public suitability and with the intention to present a range of different scenarios so as to limit feature repetition and participant habituation. Table 1. Gesture types used in SToPS ID R1 R2 R3 R4 NR1 NR2 NR3 NR4 NR5 NR6

Description Shoulder hug Handshake Hug Touching knees – sitting close One hand on shoulder (recipient standing) One hand on upper arm (recipient standing) One hand on shoulder (recipient sitting) Both hands on shoulders (recipient sitting) One hand on forearm (recipient sitting) One hand on upper arm (recipient sitting)

Figure 1. Exemplary Social Touch Picture Set images. The dotted grey outlines indicate the areas of interest used for the gaze analysis in Experiment 3.

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For each gesture, sex was controlled across four dyad variants in which the initiator sex and the receiver sex were fully balanced. Additionally, there were three different versions of each gesture depicting different actors and viewing angles. This resulted in a total of 120 touch images with 12 images (four sex dyads by three versions) for each of the 10 touch gestures. Although not used for Experiment 1, each touch image had a corresponding no-touch control in which touch actions were transformed into speech accompanying gestures or hands were made to rest on a nearby object instead of a person. Efforts were made to leave the posture of interaction partners intact and to maintain their interpersonal distance. To do this perfectly, however, was possible for the non-reciprocal touch images only where, after touch removal, the previously touching individual remained typically more active (e.g., used a more soliciting or engaging gesture) than the touch recipient. For many of the reciprocal touch images that involved touch with more than a hand (e.g., hug), posture and distance had to vary. Therefore and because there was one toucher for non-reciprocal touch but two touchers for reciprocal touch, the two types of touch were considered separately in this research. All original images – touch and no-touch controls – were complemented with a mirrored version (i.e., image content was flipped along a vertical axis: ). This was done to control for effects of gesture handedness (left vs. right hand touch). In Experiment 1, each participant saw a subset of 80 SToPS touch images – once during a frequency rating and once during a comfort rating. Image subsets were created in such a way that across participants each of the 120 SToPS touch images and their mirrored version was rated 72 times with respect to observation frequency and comfort and 36 times with respect to the frequency and comfort of performing and receiving the displayed tactile action. The two numbers were different because male and female participants could observe interactions irrespective of the characters’ sex, whereas this was not the case for performing and receiving touch. Ratings for the latter two scales required a match between the participant’s and the characters’ sex. As such, they were half as frequent as the ratings for observing touch.

Rating scales Participants were asked to report their frequency of and comfort with observing, performing, and receiving the illustrated touch gestures. Frequency was measured on a 5-point scale ranging from 0 to 4 (0 = less than once a month, 1 = once a month, 2 = once a week, 3 = once a day, 4 = more than once a day). Comfort was measured on a 5-point scale ranging from 2 to 2 ( 2 = very uncomfortable, 0 = neutral, 2 = very comfortable). Participants were asked to consider all interactions on a typical day, including those with strangers, acquaintances, friends, romantic partners, and parents and to provide an average rating.

Procedure Each participant completed the experiment in a private room. Upon arrival, they were instructed to read and sign a consent form. Subsequently, they performed a computerized rating task. Each trial in the task started with a fixation cross in the centre of the screen lasting for 300 ms. The cross was replaced by a touch image with the title of the rating construct (frequency or comfort) and the rating target (observing, receiving, or performing) shown above the image. Participants gave their response by pressing one

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of five keys. The response terminated the presentation of the image. The inter-trial interval was 500 ms long. Frequency and comfort ratings were made separately in two supra-blocks, each comprising three sub-blocks for ratings of observing, performing, and receiving the displayed touch. Participants first rated the frequency of all three actions before they moved on to rating comfort or vice versa. The order of the two supra-blocks was fully counterbalanced. The order of the three sub-blocks within each supra-block was counterbalanced using a Latin Square design. Images within each sub-block were randomly presented. Because only the observation ratings should be critical for the use of SToPS, we report only the observation ratings here. Moreover, although previous work raised the possibility of sex differences in the observation of touch (Crawford, 1994; Deethardt & Hines, 1983; Roese, Olson, Borenstein, Martin, & Shores, 1992; Willis & Dodds, 1998), these are not explored here. Sex is disregarded to preserve focus on general touch effects. We refer the interested reader to the Supporting Information in which rating scores are listed for male and female observers separately.

Results Reciprocal touch Both frequency and comfort scores were subjected to separate ANOVAs with Gesture (R1, R2, R3, R4) as the repeated measures factor and Image (original, mirrored) as the between-subjects factor. To determine the suitability of the ANOVA approach for the present data and that of Experiments 2 and 3, we probed the residual distribution of significant main effects and interactions for normality. Residuals were either normally distributed or had a super-Gaussian distribution (see Supporting Information). Because the ANOVA approach is fairly robust against small to moderate violations of the Gaussian assumption (Glass, Peckham, & Sanders, 1972; Harwell, Rubinstein, Hayes, & Olds, 1992; Schmider, Ziegler, Danay, Beyer, & B€ uhner, 2010), we continued to use ANOVAs here and elsewhere in this report. When exploring the Gesture effect, we conducted all possible pair-wise comparisons (N = 6) and corrected our p-value to p < .025 using the modified Bonferroni procedure (Keppel & Wickens, 2004). For the analysis of observation frequency, the Gesture main effect, F(3, 642) = 91.15, p < .001 and the Gesture 9 Image interaction, F(3, 642) = 4.17, p < .05) were significant. As separate one-way ANOVAs exploring the Image effect for each level of Gesture were non-significant (all ps > .1), we proceeded to explore the Gesture main effect with six two-way ANOVAs that retained the factor Image. We found that all gestures differed significantly from each other, all F(1, 214) > 18.9, p < .001. Moreover, observation frequency declined in the following order: R4 > R2 > R1 > R3. For observation comfort, statistical analysis revealed a Gesture main effect only, F(3, 642) = 76.80, p < .001. Follow-up tests revealed that participants were most comfortable observing R2, all F(1, 214) > 5.4, p < .021, followed by R4, all F(1, 214) > 70.1, p < .001. There was no difference in comfort for observing R1 and R3 (p > .1). These results are illustrated in Figure 2.

Non-reciprocal touch Frequency and Comfort scores were subjected to an ANOVA with Gesture (NR1, NR2, NR3, NR4, NR5, NR6) as the repeated measures factor and Image as the between subjects

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Figure 2. Experiment 1 norming results for reciprocal and non-reciprocal interactions. Error bars reflect the standard error of within subject effects. Frequency values were coded on a scale from 0 to 4. Comfort values were coded on a scale from 2 to 2.

factor. When exploring the Gesture effect, we conducted all possible pair-wise comparisons (N = 15) and corrected our p-value to p < .016 using the modified Bonferroni procedure (Keppel & Wickens, 2004). For observation frequency, the Gesture main effect, F(5, 1070) = 88.20, p < .001 and the Gesture 9 Image interaction, F(5, 1070) = 2.59, p < .05 were significant. Separate one-way ANOVAs revealed no significant Image effects for the different gestures (all ps > .1). Thus, we explored the Gesture main effect further using two-way ANOVAs that retained Image as a factor. We found that gesture NR1 was observed most frequently, all F(1, 214) > 10.4, p < .01, that gestures NR2 and NR6 were observed more frequently than gestures NR3, NR4, and NR5, all F(1, 214) > 35.9, p < .001, and that gesture NR4 was observed least frequently, all F(1, 214) > 62.1, p < .001. There were no significant differences between gestures NR2 and NR6 and between gestures NR3 and NR5. Analysis of observation comfort revealed a Gesture main effect only, F(5, 1070) = 24.16, p < .001. Gestures NR1 and NR2 elicited comparable comfort ratings (p > .1) that were higher than the ratings of all other gestures, all F(1, 214) > 5.6, p < .01. Ratings of gesture NR3 were indistinguishable from ratings of gestures NR1 and NR2 (ps > .1) and tended to be higher than ratings of gesture NR6, F(1, 214) = 3.8, p = .05. Gesture NR6 was rated as more comfortable than gestures NR4 and NR5, all

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F(1, 214) > 8.6, p < .01, which had comparable ratings (p > .1). The results are illustrated in Figure 2.

Discussion The primary goal of Experiment 1 was to establish the suitability of SToPS for investigating socio-emotional aspects of vicarious tactile experiences. The results of the present frequency and comfort ratings suggest such suitability. Frequency data revealed that all tactile gestures elicited a basic level of familiarity. Mean frequency ratings ranged from 1.3 for NR4 (i.e., both hands on shoulders of a sitting touch recipient) to 2.6 for gesture R4 (i.e., knees touching during close sitting). Thus, participants remembered seeing SToPS touch gestures more than once a month but less than once a day. That gestures were not reported more frequently may be due to the fact that touch is rarely an explicit observation target. Thus, like actual touch (Fisher et al., 1976), vicarious touch probably goes unnoticed, making its recollection difficult and resulting in its under-reporting. Nevertheless, the present reporting range suggests that all SToPS gestures were part of the participants’ social environment and that gesture differences were not extreme. The frequency ratings were paralleled by the comfort ratings, which ranged from 0.6 for gesture R3 (i.e., hug) to 1.2 for gesture R2 (i.e., handshake). On a scale with both negative and positive endpoints, these scores suggest mild to moderate observation comfort. Additionally, the fairly narrow rating range implies an absence of gesture outliers and reinforces the suitability of all SToPS images for the exploration of casual vicarious touch. Although all touch gestures attracted above-threshold frequency and comfort ratings, they varied significantly with respect to the rating scores. Some gestures were observed more frequently and with greater comfort than other gestures. Notably, there was correspondence across ratings (Figure 2) suggesting that more frequent forms of touch were more comfortable to observe than less frequent forms of touch. Moreover, a closer look at the kind of touch suggests that this may be related to touch intimacy (Burgoon, 1991; Burgoon et al., 1992; Pisano, Wall, & Foster, 1986). Less intimate touches such as a handshake (reciprocal) or a hand touching another’s shoulder (non-reciprocal) were rated as more frequent and comfortable than more intimate touches such as a hug (reciprocal) or the placing of two hands on another’s shoulders (non-reciprocal). To confirm these impressions, future research could ask participants to assess touch intimacy.

EXPERIMENT 2 To explore the effect of touch observation on socio-emotional processes, we presented SToPS touch and control images to participants who rated valence and arousal of the image characters and their interactions. In other words, participants described what emotion was expressed in the image. Note that this could be different from the participants’ own attitude or emotional response to the image content (Escoffier, Zhong, Schirmer, & Qiu, 2013; Gabrielsson, 2002) and as such served to discern, not the participants’ emotions, but their perception of others. In addition to valence and arousal, we asked participants to indicate how much they liked or disliked the image content. Liking and disliking are considered attitudes as they represent an overall evaluation of an object (Eagly & Chaiken, 1993; Krosnick, Judd, & Wittenbrink, 2005). As such, they helped us gauge the participants’ approach or avoidance responses.

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Drawing on prior research concerning real and vicarious touch, we predicted that, compared to no-touch control images, touch images would elicit more positive ratings and greater likeability for touchers and their interaction. Furthermore, we speculated that arousal ratings would be higher for touchers, interactions, and touch recipients in touch as compared to control images. Although many studies have shown that touch relaxes individuals and dampens the sympathetic nervous system, their focus was primarily on medical or therapeutic touch as in the context of massages (Field, Diego, & Hernandez-Reif, 2010; Krohn et al., 2011; Morhenn, Beavin, & Zak, 2012; Noto, Kitajima, Kudo, Okudera, & Hirota, 2010; Oliveira, Hachul, Goto, Tufik, & Bittencourt, 2012). Casual touch in ordinary interpersonal interactions represents a behavioural act and as such is a sign of arousal or energy. Moreover, in touch recipients it was shown to promote approach-related behaviours and to thus be behaviourally activating1 (Crusco & Wetzel, 1984; Fisher et al., 1976). Here, we predicted that observers infer these effects from images.

Methods Participants A total of 244 undergraduate students were recruited for this experiment. The data of four participants were excluded because they failed to follow instructions (N = 2) or because they encountered a technical error (N = 2). Of the remaining participants, 144 participants were presented with only the non-reciprocal touch images and their controls. These participants comprised 72 men who were on average 22.40 years old (SD = 2.09) and 72 women who were on average 20.96 years old (SD = 1.59). The remaining 96 participants were presented with only the reciprocal touch images and their controls. These participants comprised 48 men who were on average 22.24 years old (SD = 1.70) and 48 women who were on average 21.01 years old (SD = 1.34).

Images We used all 240 images from Experiment 1. Forty-eight original reciprocal interactions, 48 mirrored reciprocal interactions, 72 original non-reciprocal interactions and 72 mirrored non-reciprocal interactions were presented to four groups of participants, respectively. Each touch image had a no-touch control used within the same participants. The total number of images for this study was therefore 480.

Rating scales Participants rated each image on three 5-point Likert scales that ranged from 1 to 5. On a valence scale, they rated whether image characters and their interactions were very negative, negative, neutral, positive, or very positive. The term valence was defined to participants as referring ‘to whether an emotional state is positive or negative’. On an arousal scale, participants rated image characters and their interactions as very low, low, intermediate, high, or very high in arousal. The following definition was

1 Note that this likely depends on the emotional state of the touch recipient. In the interactions of interest here, this state was neutral. However, in other, non-ordinary interactions, the touch recipient could be negatively aroused in which case touching may have a calming effect.

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provided. ‘Arousal is the “energy level” of an emotional state (e.g., excited vs. calm). In addition, arousal is independent of whether an emotional state is positive or negative. For example, someone currently at a very low level of arousal may feel relaxed, calm, lethargic, bored, or sleepy. At the other end, someone who is at a very high level of arousal may feel stimulated, excited, frenzied, or jittery’. On a likeability scale, participants rated the image characters and their interactions as very dislikeable, dislikeable, neutral, likeable, and very likeable. Participants were told to rate how much they liked the rating target. For non-reciprocal images, the above ratings were collected for the person on the left, the person on the right, and the overall interaction. When judging the person on the left or right, participants were asked to focus on the person on the left or right, respectively, and to indicate for this person how positive, how aroused, and how likeable he or she seemed. For half the images, the person on the left was the toucher and the person on the right was the touch recipient. For the other half, toucher and touch recipient were reversed. When judging the overall interaction, participants were asked to report their summary impression of what was happening in the image. They were asked to ‘judge how positive or negative the overall interaction is’, to ‘judge the arousal level of the overall interaction between the two people’, and to ‘judge how likeable the interaction between the two people is’. For reciprocal images, participants judged only the overall interaction because here both individuals in the image were equally involved in the touch making a separate assessment obsolete.

Procedure All images were presented in the centre of a white background. A trial consisted of a 1-s fixation cross, followed by an image that remained on screen for 2.5 s. The duration of the image was selected such that it enabled participants to comfortably explore the image without allowing for too deliberate processing. The image was followed by a rating scale that stayed on screen until a response was made. The next trial started immediately after this response. Different participants rated different image sets. Participants exposed to original and mirrored reciprocal image sets completed a total of three blocks in which they rated valence, arousal, and likeability of the overall interaction, respectively. Each block comprised 96 trials, half of which were touch and half of which were control trials. Images were repeated across the three blocks within participants and rated by 48 participants each. Participants exposed to the non-reciprocal image sets completed a total of three blocks in which they rated the person on the left, the person on the right, and the overall interaction, respectively. Due to there being three rather than only one rating target, each participant rated the images for only one rating construct (i.e., valence, arousal, or likeability). There were 144 trials in each block, half of which were touch and half of which were control trials. Images were repeated across the three rating target blocks and rated by 24 participants each. Each block started with a short instruction concerning the nature of the rating (i.e., rating construct, rating target). The images within each block were presented in random order and block order was counterbalanced across participants. At the end of the experiment, participants completed a questionnaire, which included a question on the purpose of the study (‘What do you think this study is investigating?’) as well as other demographic questions.

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Results Preliminary analyses were conducted with Touch, Gesture, and Image as factors. These showed that the effect of Touch differed across Gestures and confirmed the absence of differences between original and mirrored images. The results of these analyses as well as mean rating scores for the different touch gestures are presented in the Supporting Information. In the interest of space, the following analysis is focused on the effect of Touch only.

Reciprocal touch Valence, arousal, and likeability ratings were subjected to three separate ANOVAs with Touch (touch, no-touch) as the only repeated measures factors. Each of these ANOVAs returned a significant Touch effect indicating that interactions in touch images were perceived as more positive, F(1, 95) = 344.53, p < .001, more arousing, F(1, 95) = 29.05, p < .001, and were liked better, F(1, 95) = 197.79, p < .001 than interactions in no-touch images. The results are illustrated in Figure 3.

Non-reciprocal touch The analyses for the non-reciprocal images had Touch and Rating Target (initiator, receiver, interaction) as repeated measures factor. For analysis-purposes, individuals identified as initiator and receiver in touch images maintained their status in the no-touch control images. Because of our interest in touch, we explored only Touch effects and interactions involving this factor. For valence, there was a Touch main effect, F(1, 47) = 16.18, p < .001, and a Touch 9 Rating Target interaction, F(2, 94) = 25.13, p < .001. The latter effect was explored through separate analyses for each level of Rating Target. The Touch effect was significant for all Rating Targets (overall interaction, F(1, 47) = 13.67, p < .001; initiator, F(1, 47) = 40.18, p < .001; receiver, F(1, 47) = 8.23, p < .01). However, while touch

Figure 3. Experiment 2 rating results for reciprocal interactions. Error bars reflect the standard error of within-subject effects. Rating scores were coded on scales ranging from 1 to 5.

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biased valence ratings positively for the overall interaction and the initiator, it biased valence ratings negatively for the receiver. For arousal, the Touch effect was significant, F(1, 47) = 37.82, p < .001 while the Touch 9 Rating Target interaction was not (p > .1). Touch increased arousal ratings for all three rating targets. For likeability, the analysis of non-reciprocal image ratings produced again a significant Touch effect, F(1, 47) = 5.26, p < .05. Additionally, the Touch 9 Rating Target interaction was significant, F(2, 94) = 4.06, p < .05, indicating that touch increased liking for the overall interaction, F(1, 47) = 4.59, p < .05 and the initiator, F(1, 47) = 6.09, p < .05, but not for the receiver (p > .1). The results are illustrated in Figure 4. When asked ‘What do you think this study is investigating?,’ only nine (4F, 5M) out of 96 participants in the reciprocal touch condition stated that the study might examine touch-related issues. For non-reciprocal touch, 35 (12F, 23M) out of 144 participants raised touch as a research question. Conducting an analysis without participants sensitive to the SToPS touch manipulation revealed similar results to those reported above. Moreover, all touch main effects remained significant with the exception of the likeability rating for the non-reciprocal image set. In the latter analysis, both the Touch effect, F(1, 34) = 1.19, p > .1 and Touch 9 Rating Target interaction, F(2, 68) = 0.67, p > .1 were no longer significant.

Discussion Research has shown that one individual can influence the attitudes and behaviours of another individual by engaging in casual social touch (Crusco & Wetzel, 1984; Erceau & Gu
eguen, 2007; Fisher et al., 1976; Hornik, 1992; Legg & Wilson, 2013). Such touch promotes a positive evaluation of the toucher and increases the likelihood that the touch recipient will be helpful and obliging. With Experiment 2, we sought to determine whether this phenomenon extends to bystanders, who are not part of the interaction but simply observe the tactile exchange. To this end, we presented participants with SToPS images and asked them to provide ratings with respect to valence, arousal, and likeability.

Touch and social perception Interactions and initiators were deemed more positive and excited in touch as compared to no-touch images suggesting that touching shapes impression formation in third-party observers. To others, touchers and their social exchanges appear positively emotionally activated. Additionally, the present results imply that touching alters observer attitudes. Those who touch are more liked by others than those who do not touch. Thus, the former may be more readily approached than the latter (Eagly & Chaiken, 1993; Krosnick et al., 2005). Notably, these effects were present for both reciprocal touch as well as non-reciprocal touch indicating similarities in their impact on the evaluation of touchers and touch interactions. Together, these findings extend previous research on actual physical touch by showing that third-party observers of touch share in the touch recipient’s social experiences. In addition to the third-party sharing of touch, Experiment 2 also examined how observers evaluate the targets of non-reciprocal touch. Previous reports implied that individuals who receive but do not reciprocate touch attract less favourable evaluations than control characters (Major & Heslin, 1982; Summerhayes & Suchner, 1978). The

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Figure 4. Experiment 2 rating results for non-reciprocal interactions. Error bars reflect the standard error of within-subject effects. Rating scores were coded on scales ranging from 1 to 5.

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present results both support and qualify these reports. On the one hand, they show that observers rate a person’s emotional state less positively when that person is touched as compared to when he or she is not touched. Perhaps observers interpret touch as a sign of needfulness in touch recipients. On the other hand, however, the present results show that attitudes towards touch recipients remain unaffected by the touch. Individuals are not liked less when they receive touch as compared to when they do not.

Noticing touch The images used in this study entailed dyadic interactions in which touch was not particularly emphasized. Thus, we expected that, as in physical touch studies (Fisher et al., 1976), only a subset of the participants would notice that we manipulated touch. Our findings confirmed this expectation. When asked about the study’s purpose, only 9% of participants viewing the reciprocal image set and 24% of participants viewing the non-reciprocal image set mentioned touch as a possibility. That the former set produced less touch awareness than the latter likely reflects differences in the rating procedure. For the reciprocal set, participants assessed the interaction only and viewed a total of 288 images, whereas for the non-reciprocal set, participants assessed the interaction, the toucher, and the touch recipient for a total of 432 images. Thus, by highlighting individuals in the interaction and by increasing exposure to SToPS, touch likely became more salient. Importantly, however, the number of participants noticing touch remained fairly low. Moreover, excluding this number from the statistical analysis produced touch effects that were largely similar to those obtained with all participants. The only notable difference emerged for the likeability ratings of non-reciprocal images. Here, the significant touch main effect in the full data set became non-significant in the reduced data set. This non-significance may be due to reduced power or point to a role of touch awareness. In either case, however, evidence remained for a touch influence on other social evaluations raising the possibility that this influence does not require deliberate processing of touch.

EXPERIMENT 3 Eye-tracking has become a popular tool for studying the visual exploration of scenes. Among others, much effort has been directed at examining the scanning of faces and how different aspects of the face contribute to social perception (Domes, Steiner, Porges, & Heinrichs, 2013; Hall, Hutton, & Morgan, 2010; Mazzola et al., 2006). Comparatively little research has looked at full-body scanning and the emphasis has been on which body parts observers look at (Kano, Call, & Tomonaga, 2012; Nummenmaa, Hietanen, Santtila, & Hy€ on€a, 2012) rather than on how their eye fixations change as a function of contextual or interpersonal factors. Thus, by examining the effect of touch on the visual exploration of dyadic interactions, Experiment 3 makes a unique contribution to the literature. The specific aims of Experiment 3 were to further probe the necessity of deliberate touch processing and to establish how observers explore SToPS touch and no-touch interactions visually. To this end, we presented SToPS images to participants under passive viewing conditions and measured visual exploration using eye-tracking. Specifically, we recorded the number and duration of eye fixations made to four image areas centred around the upper body of the toucher, the upper body of the touch recipient, the touching body part of the toucher, and an equivalent body part of the touch recipient (Figure 1).

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Based on previous research showing that eye fixations predict likeability (Simion, Scheier, Shimojo, & Shimojo, 2002), we expected more and longer fixations on touchers in touch as compared to control images. Additionally, we sought to determine whether potential touch effects on fixations arise from direct attention to touch. Prior work established fixations as a correlate of visual attention. It demonstrated that participants fixate on locations to which their attention shifts and that they cannot shift their attention towards locations to which they do not also shift their fixation (Hoffman & Subramaniam, 1995). In line with this work, we assumed that areas of increased fixations represent areas of increased visual attention. Moreover, if such areas included the touching body parts, touch would be processed deliberately. If, however, they were restricted to the touchers’ upper body, the touching itself would not capture attention and likely be processed incidentally, through peripheral vision only.

Methods Participants Forty-four undergraduate students were recruited for this study. For five participants, we encountered a technical error making their data unavailable for analysis. Twenty of the remaining participants were female with an average age of 21 years (SD = 1.3). The remaining 19 participants were male with an average age of 22.7 years (SD = 1.9). All participants had normal or corrected to normal vision.

Stimuli All 240 SToPS images were presented once to each participant.

Procedure At the beginning of the experiment, participants were seated in front of a 22-inch LCD monitor (Samsung SyncMaster 2233) with an NVIDIA Quadro FX 3450/4000 SD graphics card, at a viewing distance of 57 cm. The screen subtended 36.5° (horizontal) 9 27.4° (vertical) of visual angle, and all stimuli were scaled to display on the full screen (resolution: 800 9 600 pixels). The refresh rate of the display monitor was set to 120 Hz. The participant’s head was positioned within a frame against which they rested their chin and forehead. Eye movement data were recorded from the dominant eye at a sampling rate of 2,000 Hz using an EyeLink 1000 system from SR Research Ltd. The system provided head-support and monocular recordings. For the latter, eye dominance was assessed using a variant of the A-B-C vision test (Miles, 1929). A 9-point calibration and validation procedure was carried out before the images were presented and, thereafter, at intervals of 40 images. Eye movements were classified as saccades if their visual angle was larger than 0.1°, they had a minimum velocity of 30°/s, and a minimum acceleration of 8,000°/s2. Each experimental trial started with a 500 ms presentation of a white fixation cross in the middle of the screen against a grey background. This was followed by the experimental image presented on full screen for 1,500 ms. The presentation time was shorter than in Experiments 1 and 2 because our primary interest was initial fixation and we feared that prolonged presentations would bore participants in the absence of a task. In between images, a grey, blank screen was shown for a duration of 1,000–3,000 ms. Participants were instructed to naturally observe the images.

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Results Eye-tracking data were analysed using four areas of interest (AOIs). For touch images, these AOIs were defined as (1) the upper body (i.e., head to waistline, including upper arms) of the toucher in the case of non-reciprocal touch or the person on the left in the image in the case of reciprocal touch; (2) the upper body of the touch recipient or the person on the right in the image; (3) the touching body part of the toucher or the person on the left in the image (e.g., right hand); and (4) an equivalent body part of the touch recipient or person on the right in the image (e.g., right hand). For control images, same-sized AOIs were placed over equivalent body parts. Note that for reciprocal touch, the touching body parts of the person on the left and right in touch images necessarily overlapped (e.g., hands in handshake, Figure 1). Thus, although they were analysed separately, they were not fully independent. Please also note that the AOIs for the upper body were necessarily larger than the AOIs for the touching body parts. The latter were restricted by the size of the touching surfaces. However, we were unconcerned about AOI size differences as we sought to explore gaze to the different AOIs as a function of touch. We did not intend to explore gaze differences between AOIs. Fixations in the AOIs were measured across three 500 ms consecutive time-bins starting from picture onset. The number of fixations within these time-bins, as well as their average duration, was subjected to separate ANOVAs. When analysing the reciprocal image set, these ANOVAs had Touch, Time-bin (first, second, third), and AOI (left person upper body, left person touching body part, right person upper body, and right person touching body part) as repeated measures factors. When analysing the non-reciprocal image set, the AOI factor specified the upper body and touching body part of both toucher and touch recipient. Again, we analysed data for the reciprocal and non-reciprocal images separately and only report main effects of Touch and interactions involving Touch. Reciprocal touch An ANOVA with fixation numbers as the dependent variable revealed a significant Touch main effect, F(1, 38) = 95.84, p < .0001 and interactions of Touch 9 Time-bin, F(2, 76) = 6.1, p < .01, Touch 9 AOI, F(3, 114) = 40.4, p < .0001, and Touch 9 Time-bin 9 AOI, F(6, 228) = 3.6, p < .01. These results were perused further by examining the Touch 9 AOI interaction for each Time-bin. Within the first time-bin, we found a significant Touch 9 AOI interaction, F(3, 114) = 29.5, p < .0001, indicating a greater number of fixations for touch as compared to no-touch images when gazing at the upper body of interactants (person on the left, F(1, 38) = 58.5, p < .0001; person on the right, F(1, 38) = 31.8, p < .0001). The Touch effect for the interactants’ touching body parts was significant for the person on the left in the image, F(1, 38) = 15.3, p < .001, indicating that observers exhibited fewer fixations in touch as compared to no-touch control images. The Touch effect was non-significant for the person on the right in the image (p > .1). Touch effects for the upper body persisted in the second time-bin (Touch 9 AOI, F(3, 114) = 5.4, p < .01; Touch effect for person on the left, F(1, 38) = 12.3, p < .01; for person on the right, F(1, 38) = 6.07, p < .05), as well as the third time-bin (Touch 9 AOI, F(3, 114) = 22.8, p < .0001; Touch effect for person on the left, F(1, 38) = 50.2, p < .0001; for person on the right, F(1, 38) = 14.2, p < .001). In these latter time-bins, the Touch effect for the interactants’ touching body parts was non-significant (p > .1). For the duration of fixations, we observed a significant Touch main effect, F(1, 38) = 84.8, p < .0001 and a Touch 9 AOI interaction, F(3, 114) = 36.6, p < .0001.

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Figure 5. Experiment 3 eye-tracking results for reciprocal interactions. Error bars reflect the standard error of within-subject effects.

Follow-up analyses of the significant two-way interaction for each level of AOI indicated that participants made longer fixations on the interactants’ upper body in touch as compared to control images (left person, F(1, 38) = 79.2, p < .0001; right person, F(1, 38) = 43.5, p < .0001). This effect did not occur for the interactants’ touching body part (ps > .1). The results are illustrated in Figure 5.

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Non-reciprocal touch For non-reciprocal touch, analysis of the number of fixations revealed an interaction of Touch 9 Time-bin 9 AOI, F(6, 228) = 4.25, p < .001 that was explored for each Time-bin. In the first time-bin, a significant Touch 9 AOI interaction, F(3, 114) = 4.6, p < .01 indicated that the Touch effect was significant for the upper body of initiators, F(1, 38) = 3.9, p = .05 and receivers, F(1, 38) = 4.5, p < .05, but not for their touching body parts (ps > .1). Fewer fixations were made to initiators, whereas recipients received more fixations during touch as compared to no-touch trials. The Touch 9 AOI interaction was non-significant in the second time-bin. In the third time-bin, it was again significant, F(3, 114) = 2.8, p < .05 indicating that observers fixated more on the upper body of initiators, F(1, 38) = 4.3, p < .05 when there was touch as compared to no-touch. Touch effects were non-significant for receivers and touching body parts (ps > .1). An analysis of the duration of fixations revealed significant interactions of Touch 9 Time-bin 9 AOI, F(6, 228) = 3.4, p < .01. Follow-up analyses indicated that the Touch 9 AOI interaction was marginally significant in time-bins one and two, and significant in time-bin three, F(1, 38) = 3.9, p < .05. In the latter time-bin, the Touch effect approached significance for the upper body of the initiator, F(1, 38) = 3.5, p = .07 and receiver, F(1, 38) = 3.3, p = .08, and was non-significant for their touching body parts (ps > .1). While initiators tended to attract longer fixations during touch as compared to no-touch trials, the opposite was true for receivers. The results are illustrated in Figure 6.

Discussion The goal of Experiment 3 was to establish whether touch in dyadic interactions modifies observer gaze. Specifically, we asked two questions. First, we were interested in whether the increased likeability of individuals who touch as compared to those who do not touch would elicit increased fixations for the former relative to the latter. Second, as a means to gauge the potentially incidental nature of touch processing, we examined whether gaze differences would exclude image areas that displayed touch. In answer to the first question, we found more and longer fixations on individuals in reciprocal touch as compared to no-touch images. As expected, this involved individuals on the left and right who were both actively touching, increasing their joint likeability and making them both magnets for visual attention. Surprisingly, however, touchers in non-reciprocal interactions failed to consistently attract fixations. Instead, a pattern emerged suggesting opposite fixation effects for initiators and receivers across the three observation time-bins. Initially, initiators who were interactionally more active than receivers in both touch and no-touch images received fewer and shorter fixations particularly when there was touch. Later during the observation period, fixations on initiators and receivers became more similar. Moreover, now initiators tended to attract more and longer fixations during touch as compared to no-touch images, whereas the opposite was true for receivers. Together these results suggest that in non-reciprocal interactions, touch effects on fixations have several contributing factors apart from likeability. Other contributing factors may include the natural trajectory of visual attention and the perceived affect of the touch recipient as identified in Experiment 2. Specifically, the present results indicate that, initially, visual attention preferentially rests with the touch recipient rather than the toucher, possibly because the toucher’s behaviour serves as an attentional cue that directs an observer’s attention to the touch recipient as the behavioural target (Posner, 1980). Additionally, observers may seek out the touch recipient because the touching context

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Figure 6. Experiment 3 eye-tracking results for non-reciprocal interactions. Error bars reflect the standard error of within-subject effects.

implies a potentially needful state. After observers explored touch recipients, fixations shifted to touchers as a secondary observation target. In answer to our second question, we observed that the aforementioned fixation effects were restricted to the upper body of image characters, which contained the character’s face and in naturalistic settings are the principal site for social communication

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(e.g., facial expression and speech). Fixations on the touching body parts (e.g., hands) were minimal and revealed reduced rather than increased visual attention. More specifically, we found reduced gazing at the touching area of left individuals in reciprocal touch as compared to no-touch images (i.e., irrespective of initiator/receiver status). That this effect was left lateralized may be related to left-to-right reading habits or a general right hemisphere lateralization for the processing of social stimuli such as faces, voices, and gestures (Brancucci, Lucci, Mazzatenta, & Tommasi, 2009). In line with both, a touch-induced increase in the number of fixations on the upper body was also greater for individuals positioned in the left as compared to the right side of the image (Figure 5). For right individuals and for individuals in non-reciprocal interactions, fixations on the touching body parts did not differ as a function of touch. Together, these results indicate that touch failed to enhance fixations on touching body parts. Thus, one can conclude that touch failed to capture visual attention and was probably processed incidentally, through peripheral vision only.

GENERAL DISCUSSION The principal question guiding this research was whether and how the mere observation of interpersonal touch influences the observer’s socio-emotional evaluations and attitudes. To this end, we developed the SToPS comprising dyadic interactions, half of which entailed touch and half of which served as no-touch controls. In Experiments 1 and 2, we investigated observer judgments of these images, and in Experiment 3, we examined visual exploration patterns. Our results highlight a number of processing differences between touch and no-touch images indicating third-party observation effects. Importantly, many of these effects agree with findings from previous research on non-reciprocal interactions where an experimenter or confederate made short physical contact with a participant. These effects include that in the non-reciprocal interactions used here, touchers seemed more positive, were liked better, and attracted more fixations during a later viewing period than their no-touch controls. Additionally, they include touch observation effects on perceived arousal, suggesting that touch was linked to a behavioural activation. Together, these similarities between actual and observed touch suggest that vicarious tactile experiences go beyond somatosensory processing and include associated socio-emotional mechanisms. Apart from identifying similarities between physical and observed non-reciprocal touch, the present study makes a number of additional contributions. First, it extends existing research to reciprocal interactions by including images in which two individuals engaged equally in touch. As one may expect, both individuals benefited in the eye of the observer. Specifically, both elicited the rating effects described above for non-reciprocal touch. Additionally, both attracted increased fixations throughout the observation period. Second, the present study provides new insights into how observers perceive individuals who passively receive touch. These individuals are considered to feel less positively and to be more aroused relative to no-touch controls. Additionally, they are greater magnets for initial attention as indicated by eye-tracking. Thus, touching not only shapes the observer’s impression of touchers, it also shapes their impressions of touch targets. Lastly, this study addressed the mechanisms through which touch affects observers. Eye-tracking revealed that increased fixations for touch as compared to no-touch images was restricted to the interactants’ upper body, and was absent for the touching body parts. This, and the fact that the SToPS touch manipulation remained largely undetected during the rating part of this research, suggests that casual touch in SToPS images, as in real life (Fisher et al.,

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1976), is fairly inconspicuous. Moreover, it is in line with the idea that touch effects on socio-emotional evaluations occur largely through incidental processing. Apart from providing new insights, the present findings also raise questions for future research. For example, one may ask whether the observed evaluative and attitudinal effects necessitate vicarious somatosensory processing. Based on existing work on embodiment (Barsalou, 2008; Niedenthal, Barsalou, Winkielman, Krauth-Gruber, & Ric, 2005), one may reasonably assume that by activating somatosensory representations, vicarious touch triggers mechanisms that naturally interface with emotional and social processing networks in the brain. However, this assumption would need to be tested vis-a-vis the possibility that emotional and social processing occur independently of somatosensory experience, simply through the cognitive analysis of visual impressions. Other questions raised by our work concern the universality of touch effects. Given substantive evidence for cultural differences in non-verbal communication in general (Elfenbein, Beaupr
e, L
evesque, & Hess, 2007; Ishii, Kobayashi, & Kitayama, 2010; Kita, 2009) and physical contact in particular (McDaniel & Andersen, 1998; Remland, Jones, & Brinkman, 1995), one may rightly ask to what extent the present touch effects replicate across cultures. Likewise, it is still an issue whether vicarious touch experienced from images is comparable to vicarious touch experienced in real life, where observers have an actual opportunity to interact with their observation targets (Laidlaw, Foulsham, Kuhn, & Kingstone, 2011). SToPS provides a starting point from which to address these and other questions. It offers a controlled set of images that place casual touch in the social context in which it naturally occurs. Moreover, because SToPS images display various kinds of touch and are balanced between male and female actors, image subsets can be tailored for the exploration of more general issues like the ones mentioned above as well as very specific pursuits (e.g., differences in the responses to male and female handshakes). Furthermore, the emergence of touch effects within the first 500 ms following image exposure suggests that SToPS images lend themselves to methodologies that involve short exposure times (e.g., priming) and high temporal resolution (e.g., electrophysiology). In sum, with this study we extend previous research regarding casual social touch to third-party observers. We provide original evidence that observers are more interested in interactions entailing touch, that they consider touchers’ to feel more positive, and that they like touchers better than people who do not touch. Thus, we show that the socio-emotional and attitudinal changes evoked in touch recipients (e.g., Crusco & Wetzel, 1984; Fisher et al., 1976) extend to third-party observers and raise questions regarding the mechanisms underlying this phenomenon. Future research will need to address these questions and we hope that SToPS will be of use in this.

Acknowledgements The authors would like to thank Wang Shuo for help with the eye-tracking analysis and Seow Cui Shan for help with collecting the eye-tracking data. This research was supported by the A*STAR Science and Engineering Council (0921570130) and the Singapore National Research Foundation under its International Research Center Keio-NUS CUTE Center @ Singapore Funding Initiative and administered by the IDM Program Office, and the A*STAR Human Factors Engineering Thematic Strategic Research Program.

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Supporting Information The following supporting information may be found in the online edition of the article: Data S1. Overview.

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