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Personality assimilation across species: enfacing an ape reduces own intelligence and increases emotion attribution to apes

Personality assimilation across species: enfacing an ape reduces own intelligence and increases... Seeing another person’s face while that face and one’s own face are stroked synchronously or controlling a virtual face by moving one’s own induces the illusion that the other face has become a part of oneself—the enfacement effect. Here, we demonstrate that humans can enface even members of another species and that this enfacement promotes “feature migra- tion” in terms of intelligence and emotional attribution from the representation of other to the representation of oneself, and vice versa. We presented participants with a virtual human face moving in or out of sync with their own face, and then morphed it into an ape face. Participants tended to perceive the ape face as their own in the sync condition, as indicated by body-ownership and inclusion-of-others-in-the-self ratings. More interestingly, synchrony also reduced performance in a fluid-intelligence task and increased the willingness to attribute emotions to apes. These observations, which fully replicated in another experiment, fit with the idea that self and other are represented in terms of feature codes, just like non-social events (as implied by the Theory of Event Coding), so that representational self–other overlap invites illusory conjunctions of features from one representation to the other. Keywords Self-representation · Illusory conjunction · Sense of ownership · Attribution · Intelligence Introduction by moving their own hand (Slater et al., 2008). Even more important for our present purposes, people tend to perceive The ability to differentiate one’s own body from others’ is the face of another human as their own if it is stroked in syn- commonly thought to rely on continuous body representa- chrony with their own face—the enfacement illusion (Tsa- tions (Gallagher 2000; Tsakiris, 2008; Lenggenhager et al., kiris, 2008; Porciello, Bufalari, Minio-Paluello, Di Pace & 2007), which, however, can be updated and adjusted to the Aglioti, in press). present situation (e.g., Graziano & Botvinick, 2002). For Research suggests that embodying the body or face of example, the rubber hand illusion (RHI) shows that people another person does not only tend to diminish self–other perceive ownership for a rubber hand lying in front of them discrimination, but also to invite what Ma, Sellaro, Lippelt, if the rubber hand and their real hand are stroked synchro- and Hommel (2016) called “feature migration”. This hypo- nously (Botvinick & Cohen, 1998). Similarly, the virtual thetical process is derived from recent attempts to apply the hand illusion (VHI) demonstrates that people perceive own- Theory of Event Coding (TEC: Hommel, Müsseler, Ascher- ership for a virtual hand if they can operate its movements sleben & Prinz, 2001) to the representation of self and others (Hommel, Colzato & van den Wildenberg, 2009). The idea is that people represent themselves and others just like other * Bernhard Hommel perceptual events, namely, in terms of integrated networks hommel@fsw.leidenuniv.nl of sensorimotor feature codes (event files: Hommel, 2004) representing all discriminable features an event or person Cognitive Psychology Unit, Institute for Psychological consists of, such as physical attributes, affective responses, Research and Leiden Institute for Brain and Cognition, Leiden University, Wassenaarseweg 52, 2333 AK Leiden, control states, and covert and overt actions associated with The Netherlands a given event. Importantly, given that feature codes are Present Address: Key Laboratory of Personality integrated and bound together, they tend to be retrieved and Cognition, Faculty of Psychological Science, Southwest as a whole when one of the features of a given event is University, Beibei, Chongqing, China Vol.:(0123456789) 1 3 374 Psychological Research (2019) 83:373–383 encountered. Moreover, the activation of feature codes is perceived body ownership may be even more flexible than regulated by an “intentional weighting” process that gives hitherto assumed. For instance, recent studies have shown more weight to attended or task-relevant features (Memelink that people can experience ownership over avatars that are & Hommel, 2013). Accordingly, focusing on common or shaped differently from them, including not only avatars of discriminating features can reduce or increase the degree to different gender (Slater et al., 2010), race (Maister, Sebanz, which self and other are perceived as different, respectively Knoblich, & Tsakiris, 2013; Farmer, Maister, & Tsakiris, (Colzato, de Bruijn, & Hommel, 2012). Importantly for pre- 2013; Peck, Seinfeld, Aglioti, & Slater, 2013; Bufalari et al., sent purposes, to the degree that the representation of self 2014) and age (Oh et al., 2016; Banakou, Groten, & Slater, and other is perceived as part of the same event, features of 2013; Hershfield et al., 2011; Yee & Bailenson, 2006), but one’s representation can “migrate” to the representation of also avatars with very long arms (Kilteni et al., 2012), with the other (Treisman & Gelade, 1980)—i.e., features of one abnormally large and small bodies (van der Hoort, Guter- event can become part of an “illusory conjunction” with stam, & Ehrsson, 2011; see also Piryankova et al., 2014), the other. with tails (Steptoe, Steed & Slater, 2013), and with ampu- Indeed, Ma et al. (2016) observed that controlling the tated body parts (Kilteni et al., 2016). Going a step further, movements of a virtual face by moving one’s own lead to the we recently demonstrated ownership for visual objects with- migration of mood: participants were significantly happier out any obvious similarity to body parts, such as balloons and performed better in a mood-sensitive brainstorming task and rectangles (Ma & Hommel, 2015a). when controlling a smiling compared to a neutral face, but Taken together, the aforementioned findings make it plau- only if virtual and actual face moved in synchrony. In terms sible to expect illusions of this sort to be also demonstrated of TEC, experiencing a virtual happy face as being part of across species. To the best of our knowledge, only one recent oneself caused participants to confuse their own features study has addressed this issue (Ahn et al., 2016). Ahn et al. and states with the features and states of the virtual face to used immersive virtual reality to make participants viscer- the extent that affective features of the virtual face (i.e., the ally experience the life through the eyes of a cow or coral smile) became assimilated with participants’ self-representa- in an acidifying reef. When embodying a cow, participants tion. Other studies suggest that embodying another person’s walked in a virtual pasture on all fours, while eating feed hand, face, or body affects people’s attitudes towards the and drinking water, they were goaded with a virtual cat- other or the other’s social group (for a review, see Mais- tle prod and finally they were loaded onto a truck; when ter, Slater, Sanchez-Vives & Tsakiris, 2015). For example, embodying a coral on a rocky reef, participants were let occupying a virtual child body facilitates combining the to experience coral suffering from ocean acidification by self with child-like attributes in an implicit-association test seeing, hearing and feeling the reef around them as well as (Banakou, Groten, & Slater, 2013), owning a dark-skinned their own body corrode. Results showed that participants rubber hand or a black avatar reduces implicit racial bias embodying the cow or the piece of coral, compared to those of light-skinned for dark-skinned people (Maister, Sebanz, who simply watched a video of these experiences, felt more Knoblich, & Tsakiris, 2013; Farmer, Maister, & Tsakiris, connected with the nature and had more concerns about the 2013; Peck, Seinfeld, Aglioti, & Slater, 2013; but see Estu- environment. dillo & Bindemann, 2016), embodying avatars of old people, In the present study, we were interested to see whether compared to young people, reduces negative stereotyping embodiment across species can be elicited also by simply of the elderly (Yee & Bailenson, 2006), and placing partici- letting participants control the movement of a virtual face of pants in avatars with a superhero ability promotes helping a member of another species. More importantly, we aimed behavior (Rosenberg, Baughman, & Bailenson, 2013). These to assess whether enfacing members of another species observations suggest that feature migration can change both would induce self–other assimilation as observed for the attitudes and behavior, which fits with the idea that feature embodiment of human body parts. To test that possibility, codes are sensorimotor in nature, in the sense that they are we designed an ape face, which is clearly discriminable from activated by sensory information (i.e., perception) and can a human face but still keeps some degree of resemblance. regulate both perception and overt/covert behavior (Hommel To induce identification with this face we used a dynamic et al., 2001). enfacement paradigm (see Ma et al., 2016), in which par- So far, the impact of the embodiment of others was almost ticipants could move the virtual face either synchronously exclusively restricted to human bodies or body parts. Assum- or asynchronously. ing a permanent body representation, this makes sense: can- Sforza et al. (2010) reported findings showing that ques- didate effectors should be accepted as possible body parts tionnaire ratings for enfacement illusions tend to be low on only to the degree that they are similar to parts that this average, compared to ratings obtained with the RHI and representation entails (Tsakiris, Carpenter, James, & Foto- embodiment illusions. This suggests that the subjective poulou, 2010). However, there is growing evidence that experience of enfacement can be harder to obtain for faces 1 3 Psychological Research (2019) 83:373–383 375 than for other body parts, probably because facial identity (cf., Memelink & Hommel, 2013), thus introducing a con- is at the core of the sense of the self (Tsakiris, 2008). Being found and rendering our test less diagnostic. confronted with the face of a member of another species Second, we tested participants by means of an emo- is not unlikely to cause feelings of strangeness and irrita- tion rating task assessing to which degree participants tion, similar to the ones reported during virtual body illu- would attribute particular emotions to humans and apes sions (Lenggenhager et al., 2007), which might work against (Demoulin et al., 2004). As not all emotions are assumed enfacement. Therefore, to reduce the risk of incurring in to be shared among humans and other animals, we expected such irritations and to maximize the virtual enfacement that more emotions would be attributed to humans than to illusion, we used a morphing procedure in which a syn- apes, but that this difference would be reduced or elimi- chronously- or asynchronously-moving virtual human face nated after enfacing an ape. Indeed, there is evidence that slowly morphed into an ape face. Note that we applied this embodiment illusions can affect people’s perception of and technique to both synchrony conditions, so that possible beliefs towards the embodied other, and that positive self- effects of synchrony would be corrected for possible effects like associations can be extended to the embodied others on the morphing procedure itself. (Maister et al., 2015). Therefore, given that people are biased Building on earlier findings, we expected a synchro- to maintain a positive self-image (Tajfel & Turner, 1986), nously-moving virtual face to increase perceived owner- increased self–ape similarity should cause participants to ship, as measured by a standard enfacement questionnaire, attribute a higher ability to experience emotions to apes. In and increase self–ape similarity. Crucially, we hypothesized contrast, attribution of emotions to humans is not expected that ownership, in turn, should facilitate feature migration to be affected by the enfacement manipulation. Note that between the representations of self and ape. Importantly, possible synchronicity-induced changes in the attribution of according to TEC logic, feature migration of this sort can emotions to apes may be restricted to emotions that are con- involve all kind of features and can occur from the repre- sidered to be not uniquely human (i.e., primary emotions; sentation of other to the representation of oneself, and vice Epstein, 1984), or may concern primary and secondary emo- versa. tions alike. Whereas the former case would indicate that par- We tested two features that we considered particularly ticipants have judged apes from their human perspective, the diagnostic. First, we had participants to undergo the Stand- latter case would indicate that they have judged apes from ard Progressive Matrices (SPM) test (Raven, 1938), which the perspective of an ape feeling like a human. assesses fluid intelligence. Previous studies have shown that people may conform to the expected attitudes and behav- ior of the avatar they are represented by, without necessar- Methods ily being aware of that (i.e., the Proteus effect; e.g., Yee & Bailenson, 2007; Yee, Bailenson, & Ducheneaut, 2009; Participants Peña, Hancock, & Merola, 2009). For instance, participants have been found to behave more confidentially and friendlier Given the unpredictable effect sizes, the sample was cho- with strangers or to behave more aggressively during a nego- sen to double our lab standard for novel manipulations (20/ tiation when controlling attractive and tall avatars, respec- group; see Simmons, Nelson & Simonsohn, 2011). 52 vol- tively (Yee & Bailenson, 2007; see also Yee, Bailenson, & unteers participated in the study for course credit or pay but Ducheneaut, 2009). Similarly, it has been found that partici- 12 of them were excluded due to technical problems—thus pants represented by avatars dressed in Ku Klux Klan outfits leaving 40 participants (mean age 20.88 years, SD = 2.83 reported more negative and aggressive thoughts than those years, range 18–29 years; seven males). We used the depart- dressed as doctors (Peña et al., 2009). Taken together, these ment’s standard advertisement system and accepted all par- findings are consistent with previous literature showing that ticipants registering in the first (and only) wave. Written trait concepts and stereotypes become active automatically informed consent was obtained from all participants before in the presence of relevant behavior or stereotyped-group the experiment. Participants were naive as to the purposes of features (i.e., through perception), and can cause people to the experiment. The study conformed to the ethical standards behave consistently with the activated stereotypes (Char- of the declaration of Helsinki and the protocol was approved trand & Bargh, 1999). Therefore, considering the common by the local research ethics committee. stereotype that humans are more intelligent than non-human animals, we predicted that enfacing and, thus, in some sense Experimental setup becoming an ape should reduce intelligence and result in a lower score in the SPM test. Note that we relied on, but did Figure 1 shows the basic setup. The virtual faces were con- not directly test this stereotype in our participants because structed and controlled by means of virtual reality environ- the assessment would have primed the respective stereotype ment software (Vizard and FAAST; Suma et al., 2013). We 1 3 376 Psychological Research (2019) 83:373–383 Fig. 1 The experimental setup. The participant’s facial move- the Kinect system, which requires a minimum distance of 1.8  m to ments were monitored by means of a Kinect system (recording recognize human movements. Participants (here the first author) frame rate = 30  Hz) and an Intersense orientation tracker (update wore a cap with an orientation tracker attached on it (see right yel- rate = 180 Hz). The Kinect system (see upper left yellow frame) was low frame). Computer tasks (i.e., the emotion rating and the Raven’s located behind and above the computer screen showing the virtual Standard Progressive Matrices tasks) were presented on a second face (see lower left yellow frame). Participants sat at about 2 m from screen located next to the screen showing the virtual face used Vizard to build three three-dimensional virtual faces, where the ape face on the screen was”) is a location-related one for each gender, based on average Caucasian faces (e.g., ownership item that is sometimes aggregated with direct Jones et al., 2006) and one for the ape face. A computer- ownership to assess perceived ownership properly (Kalck- ized morphing procedure was used to gradually merge the ert & Ehrsson, 2014), Q3 (“It seemed like my own face human and the ape faces (see Fig. 2). By integrating Kinect, began to resemble the ape face on the screen”) assesses Intersense, FAAST, and Vizard, our setup allowed partici- perceived appearance similarity, a possible correlate of pants to freely move or rotate their own face to control the ownership (Tajadura-Jiménez et  al., 2012), and Q4 (“I movement or rotation of the virtual face, with a latency of could control the ape face”) perceived agency, which about 40 ms—a value far below the 300-ms threshold pro- according to Ma and Hommel (2015b) predict ownership posed by Shimada, Fukuda, and Hiraki (2009) as the critical in participant-active setups. For each item, participants time window allowing for the occurrence of multi-sensory chose a score on a Likert scale ranging from 1 (“strongly integration processes constituting self-body representation. disagree”) to 7 (“strongly agree”). Note that we did not use the “control” questions of the RHI questionnaire, as in our Measures previous studies (Ma & Hommel, 2015a, 2015b) we found evidence suggesting that, for illusions created using VR, Enfacement questionnaire synchrony is likely to affect responses to control questions as well. This is likely because dynamic manipulations, Four items were adopted from the standard RHI question- compared to the static ones, can make all self-perception naire (Botvinick & Cohen, 1998) and enfacement studies aspects perceivable or salient, thereby producing measur- (Tajadura-Jiménez, Grehl, S., & Tsakiris, 2012; Sforza able synchrony effects on all items relating to any aspect et al., 2010). Q1 (“I felt the ape face was my own face”) of self-perception that can correlate with ownership and directly addresses perceived ownership, Q2 (“It seemed agency (cf., Ma & Hommel, 2015b). like I was sensing the movement of my face in the location 1 3 Psychological Research (2019) 83:373–383 377 Fig. 2 Some representative images resulting from the morphing 25% ape, 50% human and 50% ape, 25% human and 75% ape, and procedure applied to male (upper panel) and female (lower panel) 0% human and 100% ape. The resulting 100% ape face was identical faces. From left to right, 100% human and 0% ape, 75% human and regardless of whether the male or the female face was morphed (Epstein, 1984; Demoulin et al., 2004), 6 primary (affec- Including others in the self (IOS) scale tion, pleasure, attraction, fear, exhaustion, and pain) and 6 secondary emotions (admiration, hope, surprise, embar- A variant of the IOS scale (Aron, Aron, & Smollan, 1992) assessed subjective aspects of self–other integration. The rassment, contempt, humiliation). Each participant per- formed two task blocks, one in which emotions were rated scale consists of seven Venn diagram-like pairs of circles representing varying degrees of self–other overlap (i.e., sub- for Human and one in which they were rated for Ape. The order of the two blocks was counterbalanced across partici- jective self–other integration). Participants are to choose the overlap that they think represents best the degree to which pants, and within each block emotions were presented in a random order. the virtual face looks like their own, how familiar it feels to them. Procedure Raven’s standard progressive matrices (SPM) After having read and signed the informed consent, partici- SPMs (Raven, 1938) assessed participants’ fluid intelli- pants were seated in front of a computer monitor and to wear the cap (as shown in Fig. 1). Each participant underwent two gence. The test consists of 60 trials of increasing difficulty. Participants either received the even 30 trials on the first synchrony (synchronous and the asynchronous) conditions in counterbalanced order. During both synchrony conditions, experimental condition and the odd 30 trials on the sec- ond experimental condition or vice versa (counterbalanced the participants actively operated the virtual face for 3 min by freely displacing or rotating their own face, which led across participants). to corresponding displacement or rotation movements of the virtual face. The 3-min interval was divided into three Emotion rating task parts. During the first 30 s, participants were presented with either the male or the female virtual face (depending on their The emotion rating task was adopted from De Dreu et al. (2011). Participants were asked to rate, on a Likert scale gender), which was 100% human. Then, for the next 120 s, the human face was morphed into the ape face (from 100% ranging from 1 (not at all) to 7 (very much), how much humans and apes are able to experience 12 emotions human–0% ape to 0% human–100% ape, in steps of 0.83% 1 3 378 Psychological Research (2019) 83:373–383 every second, for a total of 120 morphs, plus the two cor- Results responding mapped texture pictures, each for male or female participants; see Fig. 2 for representative images resulting Enfacement questionnaire from the morphing procedure). For the remaining 30 s, the viewed face was 100% ape. Shapiro–Wilk test revealed that the distribution of the dif- The only difference between the two conditions per- ferences deviated significantly from the normal distribution tained to the temporal delay between people’s own move- for Q2, Q3 and Q4 (p ≤ 0.04), but not for Q1 (p = 0.06). ments and that of the virtual face, which—excluding the Because the data were not normally distributed for three out 40-ms time delay caused by the equipment—was either of four questionnaire items, the non-parametric Wilcoxon 0 s (= synchronous) or 3 s (= asynchronous). Immediately signed-rank test was used to compare ratings across the two after each synchrony condition, participants answered the synchrony conditions. For non-symmetrically shaped distri- enfacement questionnaire, responded to the IOS scale, per- butions values resulting from the non-parametric sign test formed the emotion rating and eventually the Raven task. We are reported. Analyses showed that synchrony was signifi- preferred not to counterbalance the order of the Raven and cant for all items (Q1: Z = − 3.85, p < 0.001, r = 0.61; Q2: the emotion rating tasks for the following reason. Research Z = − 4.50, p < 0.001, r = 0.71; Q3: Z = − 3.47, p < 0.001, has shown that performing a demanding cognitive task is r = 0.55; Q4: Z = − 4.53, p < 0.001, r = 0.72), with par tici- likely to reduce self-control (i.e., it can cause ego-depletion; pants experiencing more ownership, similarity, and agency Baumeister, Bratslavsky, Muraven, & Tice, 1998), and evi- in the synchronous than in the asynchronous condition. dence exists that lack of self-control can affect interpersonal Hence, we successfully induced a virtual enfacement illu- perception (e.g., Vohs & Ciarocco, 2004; Govorun, & Payne, sion for the ape face. Table 1 provides participants’ ratings 2006). Therefore, to avoid possible confounding effects (i.e., median and range in parentheses) separately for each resulting from ego-depletion we preferred to have partici- item and for the aggregated ownership items (Q1–Q2) as a pants perform the most demanding task (i.e., the Raven task) function of synchrony condition. after the emotion ratings task. All participants were asked to take a 5-min break between the two synchrony conditions. IOS Shapiro–Wilk test revealed that the distribution of the dif- ferences deviated significantly from the normal distribution (p = 0.002). A Wilcoxon signed-rank test showed that the synchrony effect was significant, indicating that participants Table 1 Overview of Measure Experiment Replication participants’ performance for all dependent measures as a Synchrony Asynchrony Synchrony Asynchrony function of synchrony Enfacement questionnaire (median and range)  Direct ownership (Q1) 4.0 (6) 2.0 (6) 3.0 (5) 2.0 (6)  Location (Q2) 5.5 (6) 3.0 (6) 5.0 (6) 2.0 (5)  Aggregated ownership (Q1-Q2) 4.5 (6) 2.75 (6) 4.0 (5) 2.5 (5.5)  Similarity (Q3) 3.0 (6) 2.0 (5) 2.0 (6) 2.0 (5)  Agency (Q4) 6.0 (6) 4.0 (6) 6.5 (6) 4.5 (6) IOS (median and range) 4.5 (6) 3.0 (6) 4.0 (5) 3.0 (5) Raven (median and range) 25.0 (13) 26.0 (12) 25.0 (9) 26.0 (10) Emotion rating (mean and standard error of the mean) ns  Human (primary) 6.63 (0.07) 6.65 (0.06) 6.71 (0.07) 6.69 (0.08) ns  Human (secondary) 6.58 (0.08) 6.63 (0.09) 6.48 (0.12) 6.55 (0.11)  Ape (primary) 6.07 (0.10) 5.95 (0.11) 5.71 (0.14) 5.36 (0.22)  Ape (secondary) 4.78 (0.19) 4.50 (0.22) 4.33 (0.19) 3.89 (0.24) Median values and range (in parentheses) are reported for the enfacement questionnaire items, IOS and Raven, whereas means and standard error of the mean (in parentheses) are reported for the emotion rating task. Significant and non-significant synchrony effects are indicated by “ ” and “ns”, respectively. Columns 2 and 3 show results for the original experiment, and columns 4 and 5 for the replication 1 3 Psychological Research (2019) 83:373–383 379 experienced greater overlap with the virtual face after the syn- Replication chronous than after the asynchronous condition, Z = − 4.45, p < 0.001, r = 0.70, see Table 1. While the findings came out as expected, some of the effects were rather small numerically and just reached the significance SPM level. To make sure that our conclusions are not based on spu- rious, non-reproducible findings, we conducted an exact repli- Shapiro–Wilk test revealed that the distribution of the dif- cation study. 40 new participants were tested, and the statistical ferences deviated significantly from the normal distribution findings were exactly as in the first experiment: the synchrony (p = 0.043). A sign test showed that the synchrony effect was effect was significant for all enfacement questionnaire items significant, with a significant median decrease in Raven scores (Q1: Z = − 2.35, p = 0.02, r = 0.37; Q2: Z = − 5.13, p < 0.001, after the synchronous condition, compared to the asynchro- r = 0.81; Q3: Z = − 2.62, p = 0.01, r = 0.41; Q4: Z = − 3.85, nous one, Z = − 2.03, p = 0.043, r = 0.32, see Table 1. p < 0.001, r = 0.61), IOS ratings, Z = − 3.40, p < 0.001, r = 0.54, Raven scores, Z = − 2.34, p = 0.02, r = 0.37, and a significant Emotion ratings two-way interaction involving the factors synchrony and spe- cies was found for the emotion rating task, F(1,39) = 9.46, Shapiro–Wilk test indicated that residuals were not normally p = 0.004, ηp2 = 0.20, with synchronicity affecting emotion distributed for the majority of factor level combinations ratings when judging apes but not when judging humans (see (p < 0.05). However, due to the central limit theorem, the Table 1). ANOVA can be considered robust to violations of normal- ity (Glass, Peckham & Sanders, 1972; Harwell, Rubinstein, Correlations Hayes & Olds, 1992; Schmider, Ziegler, Danay, Beyer, & Bühner, 2010). Therefore, ratings were analyzed by means Next, we combined the data of the two experiments to assess of a repeated-measure ANOVA with synchrony (synchro- the relationship between perceived ownership and ownership- nous vs. asynchronous), species (human vs. ape) and emo- related characteristics (self–other similarity and agency), and tion type (primary vs. secondary) as within-participant fac- between these factors and task (emotion ratings for Ape and tors. ANOVA revealed significant main effects of emotion Raven) performance. The degrees of ownership (as assessed type, F(1,39) = 65.39, p < 0.001, ηp2 = 0.63, and species, by the aggregation of Q1–2), agency (Q4), and self–other simi- F(1,39) = 86.27, p < 0.001, ηp2 = 0.69: ratings were higher larity (IOS ratings) were computed by subtracting asynchro- for primary than for secondary emotions (6.3 vs. 5.6) and, as nous ratings from synchronous ratings. Likewise, synchrony- expected, for humans than for apes (6.6 vs. 5.3). Moreover, a induced changes in task performance were computed by significant interaction involving the factor species and emo- subtracting emotion ratings for Ape and Raven scores observed tion type was found, F(1,39) = 71.07, p < 0.001, ηp2 = 0.65. after the asynchronous condition from those observed after Consistent with previous findings (Epstein, 1984; Demoulin the synchronous condition. We computed one-tailed Spearman et al., 2004), Bonferroni post hoc tests revealed that partici- correlations among changes in ownership, agency and IOS pants judged apes to be able to feel primary emotions to a ratings, and synchrony-induced changes in task performance. greater extent than secondary emotions (6.0 vs. 4.6, p < 0.001), Significant and positive correlations were observed between whereas no difference between primary and secondary emo- ownership and IOS changes, rho = 0.45, p < 0.001, ownership tions was found when rating human emotions (6.6 vs. 6.6, and agency changes, rho = 0.24, p = 0.017, and between agency p = 1). More importantly, the interaction between synchrony and IOS changes, rho = 0.41, p < 0.001. Interestingly, emotion and species was also significant, F (1,39) = 6.22, p = 0.017, rating changes correlated positively with agency, rho = 0.40, ηp2 = 0.14. Bonferroni post hoc tests confirmed that par- p < 0.001, and IOS changes, rho = 0.29, p = 0.004, and nega- ticipants attributed to apes a higher capacity to feel emo- tively with Raven changes, r = − 0.26, p = 0.010. No other sig- tions in the synchronous than in the asynchronous condition nificant correlations were found, absolute rho values ≤ 0.09, (p = 0.03), whereas no difference between the two synchrony ps ≥ 0.22. conditions was observed when rating human emotions (p = 1; see Table 1). No other significant sources of variance were observed, F ≤ 2.78, p ≥ 0.10. Discussion s s This study set out to test whether embodiment can be dem- onstrated across species and whether this would induce self–other assimilation (and feature migration) in terms of intelligence and emotion attribution—as implied by our 1 3 380 Psychological Research (2019) 83:373–383 application of TEC (Hommel et al., 2001). The first ques- demonstration of feature migration in the sense of Ma et al. tion can be answered ar ffi matively: when the ape face moved (2016): increasing the overlap of self- and other-represen- in synchrony with the participants’ own face, they were tation invites illusionary conjunctions, in which features of more likely to perceive ownership for the former. It is true the other become features of oneself. Moreover, enfacing an that ownership perception was not perfect, as the score fell ape tempted participants to attribute more emotions to apes, into the midrange of the scale—a finding that is consistent another case of feature migration: when becoming more like with other studies of the virtual-hand (e.g., Ma & Hommel, an ape, participants took their emotional capabilities with 2015a, 2015b) and the virtual-face illusion (Ma et al., 2016; them, so to speak. Note that synchrony affected primary and Tajadura-Jiménez et al., 2012; Sforza et al., 2010). This limi- secondary emotions alike. While primary emotions are con- tation notwithstanding, the fact that a short practice over 3 sidered to be shared among humans and other highly evolved min was sufficient to affect one’s identification with another animals, secondary emotions are commonly thought to be species—which most participants were likely to have little uniquely human (Epstein, 1984). If our human participants experience with—must be considered notable. Converging would have judged apes from their human perspective, one evidence supporting the conclusion that our participants might have expected that synchrony has a stronger impact identified with the virtual ape comes from the IOS ratings, on primary emotions attributed to apes than on secondary which confirm that synchrony increased the perceived over - emotions. However, given that synchrony enhanced the attri- lap between participant and ape. Hence, humans are able bution of both kinds of emotions, it seems that the emotion to identify with a member of another species, probably in a attribution in this condition relied on a more “insider per- similar way as they can embody the hand or face of another spective”, that is, from the perspective of an ape feeling like human. This result is not unanticipated as it fits with previ- a human. In other words, when embodying another person ous claims that people’s self-construal is dynamic and sensi- (or a member of another species), self-related attributes can tive to situational and cultural biases (Colzato et al., 2012; be extended to the embodied others who become more like Kühnen & Oyserman, 2002), and that people are rather the self. This fits with the observation that synchrony had flexible regarding which objects and events they consider no effect on the attribution of emotions to humans, which as being part of their body—as long as they can control also rules out the possibility that the enfacement experience the behavior of these objects and events (Ahn et al., 2016; facilitated emotion attribution in general. Kilteni et al., 2016; Ma & Hommel, 2015a, b; Piryankova In the present study, we were interested to see whether et al., 2014; Steptoe et al., 2013; Kilteni et al., 2012; van feature migration can lead to the integration of features der Hoort et al., 2011). It is worth noting that, in the present of another individual into the representation of oneself. study, to maximize the chance of eliciting a virtual enface- However, we would like to emphasize that, theoretically ment illusion of an ape face, we made use of a morphing speaking, features would be expected to migrate both procedure in which a synchronously or asynchronously mov- ways: from other to self and from self to other. So, while ing virtual human face slowly morphed into an ape face. As our present study was tapping into the route from other to mentioned in the Introduction, such a choice was aimed at self, some recent studies have provided evidence that fea- counteracting possible feelings of irritation and strangeness tures may migrate from self to other as well. For instance, that could have arisen by confronting participants directly body-ownership illusions have been found to induce a more with the face of a member of another species. It remains to positive attitude toward social out-groups (e.g., Maister be established whether the morphing procedure was really et al., 2015), which from our theoretical view might sug- necessary for the illusion to occur, or whether virtual enface- gest that a positive self-image can migrate to an embod- ment of a member of a different species can also be obtained ied other. Indeed, considering that attributing emotions to without such a procedure. outgroup members represents an attitude, our findings are The second most important question can also be answered consistent with, and can be seen as an extension of previous affirmatively: both the intelligence measure and the emotion outgroup studies along the lines of Maister et al. (2015). attributions were affected by synchrony. As predicted from As already mentioned, synchronous stimulation of partici- our TEC-based approach, perceiving oneself to own an ape pants’ own hand and a rubber hand typical for a racial out- face made people behave less intelligently; that is, partici- group member increased perceived ownership for the rub- pants tended to adopt the intellectual characteristics humans ber hand and induced a more positive attitude toward that attribute to the species they perceived themselves to become outgroup (Farmer et al., 2013). Similarly, Inzlicht, Gutsell, a part of, thereby confirming previous findings document - and Legault (2012) reported that negative attitudes toward ing people’s tendency to adopt attitudes and behavior of the a racial outgroup were reduced by synchronizing one’s own avatar they are represented by (i.e., the Proteus effect; e.g., movements with those of an outgroup member. It is true Yee & Bailenson, 2007; Yee, Bailenson, & Ducheneaut, that such a modulation of implicit racial attitudes has not 2009; Peña, Hancock, & Merola, 2009). We consider this a been observed in a recent study using a static enfacement 1 3 Psychological Research (2019) 83:373–383 381 paradigm (Estudillo & Bindemann, 2016). This suggests et  al. (2013) and Inzlicht et  al. (2012). Notwithstanding that embodiment illusions are not always effective in biasing these interesting open questions, our findings provide fur - self- and/or other-perception, especially when concerning ther evidence that the boundaries between perceived self and body parts that are strongly tied to the self-identity, just like perceived other are rather flexible, and that representational faces. However, recent comparisons between dynamic and self–other overlap invites illusory conjunctions of features static hand illusion conditions have revealed that dynamic from one representation to the other—including others of conditions, as used in the present study, are much more sen- another species. sitive to manipulations and strongly increase the coherence Acknowledgements The research was supported by a post-graduate between dependent measures (Ma & Hommel, 2015a, b). It scholarship of the China Scholarship Council (CSC) to KM, and an is thus possible that dynamic conditions, perhaps together infrastructure grant of the Netherlands Research Organization (NWO) with the morphing technique we used in the present study, to BH. will be more successful in demonstrating modifications of racial attitudes. Author contributions The study is based on the idea of KM, who also developed the technical design of the study, collected and analyzed Note that in the present study we relied on explicit meas- the data, and prepared the first draft. RS and BH contributed to the ures but did not use implicit measures of ownership, a deci- development of the study concept and to the analysis and interpretation sion we made for two reasons. First, explicit and implicit of the data, and they provided critical revisions. All authors approved measures of body ownership have often been demonstrated the final version of the manuscript. to dissociate (e.g., Liepelt, Dolk & Hommel, 2017; Ma & Hommel, 2015a, b). This implies that explicit and implicit Compliance with ethical standards measures rely on different kinds of information, and so far, Conflict of interest The authors declare that they had no conflicts of in- no theoretical account for such dissociations has been sug- terest with respect to their authorship or the publication of this article. gested. This renders it unclear what kind of information implicit measures would add and which theoretical implica- Ethical standards All procedures performed were in accordance with the ethical standards of the institutional research committee and with tions the convergence or divergence with explicit measures the 1964 Helsinki declaration and its later amendments. would have. Second, the inclusion of implicit measures was unlikely to be successful in our study. Previous face-owner- ship studies have used self–other discrimination or recogni- Open Access This article is distributed under the terms of the Crea- tive Commons Attribution 4.0 International License (http://creat iveco tion of self–other morphed faces (e.g., Sforza et al., 2010; mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- Tsakiris, 2008; Tajadura-Jiménez et al., 2012) as an implicit tion, and reproduction in any medium, provided you give appropriate measure. The typical outcome was the tendency of partici- credit to the original author(s) and the source, provide a link to the pants to under-discriminate between pictures of oneself and Creative Commons license, and indicate if changes were made. of a very similar human other in the synchrony, compared to the asynchrony condition. This bias is commonly very small (around 5%), which renders it extremely unlikely to References get anything measurable when comparing oneself against the picture of an ape. 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Personality assimilation across species: enfacing an ape reduces own intelligence and increases emotion attribution to apes

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Springer Journals
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Copyright © 2018 by The Author(s)
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Psychology; Psychology Research
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0340-0727
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10.1007/s00426-018-1048-x
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Abstract

Seeing another person’s face while that face and one’s own face are stroked synchronously or controlling a virtual face by moving one’s own induces the illusion that the other face has become a part of oneself—the enfacement effect. Here, we demonstrate that humans can enface even members of another species and that this enfacement promotes “feature migra- tion” in terms of intelligence and emotional attribution from the representation of other to the representation of oneself, and vice versa. We presented participants with a virtual human face moving in or out of sync with their own face, and then morphed it into an ape face. Participants tended to perceive the ape face as their own in the sync condition, as indicated by body-ownership and inclusion-of-others-in-the-self ratings. More interestingly, synchrony also reduced performance in a fluid-intelligence task and increased the willingness to attribute emotions to apes. These observations, which fully replicated in another experiment, fit with the idea that self and other are represented in terms of feature codes, just like non-social events (as implied by the Theory of Event Coding), so that representational self–other overlap invites illusory conjunctions of features from one representation to the other. Keywords Self-representation · Illusory conjunction · Sense of ownership · Attribution · Intelligence Introduction by moving their own hand (Slater et al., 2008). Even more important for our present purposes, people tend to perceive The ability to differentiate one’s own body from others’ is the face of another human as their own if it is stroked in syn- commonly thought to rely on continuous body representa- chrony with their own face—the enfacement illusion (Tsa- tions (Gallagher 2000; Tsakiris, 2008; Lenggenhager et al., kiris, 2008; Porciello, Bufalari, Minio-Paluello, Di Pace & 2007), which, however, can be updated and adjusted to the Aglioti, in press). present situation (e.g., Graziano & Botvinick, 2002). For Research suggests that embodying the body or face of example, the rubber hand illusion (RHI) shows that people another person does not only tend to diminish self–other perceive ownership for a rubber hand lying in front of them discrimination, but also to invite what Ma, Sellaro, Lippelt, if the rubber hand and their real hand are stroked synchro- and Hommel (2016) called “feature migration”. This hypo- nously (Botvinick & Cohen, 1998). Similarly, the virtual thetical process is derived from recent attempts to apply the hand illusion (VHI) demonstrates that people perceive own- Theory of Event Coding (TEC: Hommel, Müsseler, Ascher- ership for a virtual hand if they can operate its movements sleben & Prinz, 2001) to the representation of self and others (Hommel, Colzato & van den Wildenberg, 2009). The idea is that people represent themselves and others just like other * Bernhard Hommel perceptual events, namely, in terms of integrated networks hommel@fsw.leidenuniv.nl of sensorimotor feature codes (event files: Hommel, 2004) representing all discriminable features an event or person Cognitive Psychology Unit, Institute for Psychological consists of, such as physical attributes, affective responses, Research and Leiden Institute for Brain and Cognition, Leiden University, Wassenaarseweg 52, 2333 AK Leiden, control states, and covert and overt actions associated with The Netherlands a given event. Importantly, given that feature codes are Present Address: Key Laboratory of Personality integrated and bound together, they tend to be retrieved and Cognition, Faculty of Psychological Science, Southwest as a whole when one of the features of a given event is University, Beibei, Chongqing, China Vol.:(0123456789) 1 3 374 Psychological Research (2019) 83:373–383 encountered. Moreover, the activation of feature codes is perceived body ownership may be even more flexible than regulated by an “intentional weighting” process that gives hitherto assumed. For instance, recent studies have shown more weight to attended or task-relevant features (Memelink that people can experience ownership over avatars that are & Hommel, 2013). Accordingly, focusing on common or shaped differently from them, including not only avatars of discriminating features can reduce or increase the degree to different gender (Slater et al., 2010), race (Maister, Sebanz, which self and other are perceived as different, respectively Knoblich, & Tsakiris, 2013; Farmer, Maister, & Tsakiris, (Colzato, de Bruijn, & Hommel, 2012). Importantly for pre- 2013; Peck, Seinfeld, Aglioti, & Slater, 2013; Bufalari et al., sent purposes, to the degree that the representation of self 2014) and age (Oh et al., 2016; Banakou, Groten, & Slater, and other is perceived as part of the same event, features of 2013; Hershfield et al., 2011; Yee & Bailenson, 2006), but one’s representation can “migrate” to the representation of also avatars with very long arms (Kilteni et al., 2012), with the other (Treisman & Gelade, 1980)—i.e., features of one abnormally large and small bodies (van der Hoort, Guter- event can become part of an “illusory conjunction” with stam, & Ehrsson, 2011; see also Piryankova et al., 2014), the other. with tails (Steptoe, Steed & Slater, 2013), and with ampu- Indeed, Ma et al. (2016) observed that controlling the tated body parts (Kilteni et al., 2016). Going a step further, movements of a virtual face by moving one’s own lead to the we recently demonstrated ownership for visual objects with- migration of mood: participants were significantly happier out any obvious similarity to body parts, such as balloons and performed better in a mood-sensitive brainstorming task and rectangles (Ma & Hommel, 2015a). when controlling a smiling compared to a neutral face, but Taken together, the aforementioned findings make it plau- only if virtual and actual face moved in synchrony. In terms sible to expect illusions of this sort to be also demonstrated of TEC, experiencing a virtual happy face as being part of across species. To the best of our knowledge, only one recent oneself caused participants to confuse their own features study has addressed this issue (Ahn et al., 2016). Ahn et al. and states with the features and states of the virtual face to used immersive virtual reality to make participants viscer- the extent that affective features of the virtual face (i.e., the ally experience the life through the eyes of a cow or coral smile) became assimilated with participants’ self-representa- in an acidifying reef. When embodying a cow, participants tion. Other studies suggest that embodying another person’s walked in a virtual pasture on all fours, while eating feed hand, face, or body affects people’s attitudes towards the and drinking water, they were goaded with a virtual cat- other or the other’s social group (for a review, see Mais- tle prod and finally they were loaded onto a truck; when ter, Slater, Sanchez-Vives & Tsakiris, 2015). For example, embodying a coral on a rocky reef, participants were let occupying a virtual child body facilitates combining the to experience coral suffering from ocean acidification by self with child-like attributes in an implicit-association test seeing, hearing and feeling the reef around them as well as (Banakou, Groten, & Slater, 2013), owning a dark-skinned their own body corrode. Results showed that participants rubber hand or a black avatar reduces implicit racial bias embodying the cow or the piece of coral, compared to those of light-skinned for dark-skinned people (Maister, Sebanz, who simply watched a video of these experiences, felt more Knoblich, & Tsakiris, 2013; Farmer, Maister, & Tsakiris, connected with the nature and had more concerns about the 2013; Peck, Seinfeld, Aglioti, & Slater, 2013; but see Estu- environment. dillo & Bindemann, 2016), embodying avatars of old people, In the present study, we were interested to see whether compared to young people, reduces negative stereotyping embodiment across species can be elicited also by simply of the elderly (Yee & Bailenson, 2006), and placing partici- letting participants control the movement of a virtual face of pants in avatars with a superhero ability promotes helping a member of another species. More importantly, we aimed behavior (Rosenberg, Baughman, & Bailenson, 2013). These to assess whether enfacing members of another species observations suggest that feature migration can change both would induce self–other assimilation as observed for the attitudes and behavior, which fits with the idea that feature embodiment of human body parts. To test that possibility, codes are sensorimotor in nature, in the sense that they are we designed an ape face, which is clearly discriminable from activated by sensory information (i.e., perception) and can a human face but still keeps some degree of resemblance. regulate both perception and overt/covert behavior (Hommel To induce identification with this face we used a dynamic et al., 2001). enfacement paradigm (see Ma et al., 2016), in which par- So far, the impact of the embodiment of others was almost ticipants could move the virtual face either synchronously exclusively restricted to human bodies or body parts. Assum- or asynchronously. ing a permanent body representation, this makes sense: can- Sforza et al. (2010) reported findings showing that ques- didate effectors should be accepted as possible body parts tionnaire ratings for enfacement illusions tend to be low on only to the degree that they are similar to parts that this average, compared to ratings obtained with the RHI and representation entails (Tsakiris, Carpenter, James, & Foto- embodiment illusions. This suggests that the subjective poulou, 2010). However, there is growing evidence that experience of enfacement can be harder to obtain for faces 1 3 Psychological Research (2019) 83:373–383 375 than for other body parts, probably because facial identity (cf., Memelink & Hommel, 2013), thus introducing a con- is at the core of the sense of the self (Tsakiris, 2008). Being found and rendering our test less diagnostic. confronted with the face of a member of another species Second, we tested participants by means of an emo- is not unlikely to cause feelings of strangeness and irrita- tion rating task assessing to which degree participants tion, similar to the ones reported during virtual body illu- would attribute particular emotions to humans and apes sions (Lenggenhager et al., 2007), which might work against (Demoulin et al., 2004). As not all emotions are assumed enfacement. Therefore, to reduce the risk of incurring in to be shared among humans and other animals, we expected such irritations and to maximize the virtual enfacement that more emotions would be attributed to humans than to illusion, we used a morphing procedure in which a syn- apes, but that this difference would be reduced or elimi- chronously- or asynchronously-moving virtual human face nated after enfacing an ape. Indeed, there is evidence that slowly morphed into an ape face. Note that we applied this embodiment illusions can affect people’s perception of and technique to both synchrony conditions, so that possible beliefs towards the embodied other, and that positive self- effects of synchrony would be corrected for possible effects like associations can be extended to the embodied others on the morphing procedure itself. (Maister et al., 2015). Therefore, given that people are biased Building on earlier findings, we expected a synchro- to maintain a positive self-image (Tajfel & Turner, 1986), nously-moving virtual face to increase perceived owner- increased self–ape similarity should cause participants to ship, as measured by a standard enfacement questionnaire, attribute a higher ability to experience emotions to apes. In and increase self–ape similarity. Crucially, we hypothesized contrast, attribution of emotions to humans is not expected that ownership, in turn, should facilitate feature migration to be affected by the enfacement manipulation. Note that between the representations of self and ape. Importantly, possible synchronicity-induced changes in the attribution of according to TEC logic, feature migration of this sort can emotions to apes may be restricted to emotions that are con- involve all kind of features and can occur from the repre- sidered to be not uniquely human (i.e., primary emotions; sentation of other to the representation of oneself, and vice Epstein, 1984), or may concern primary and secondary emo- versa. tions alike. Whereas the former case would indicate that par- We tested two features that we considered particularly ticipants have judged apes from their human perspective, the diagnostic. First, we had participants to undergo the Stand- latter case would indicate that they have judged apes from ard Progressive Matrices (SPM) test (Raven, 1938), which the perspective of an ape feeling like a human. assesses fluid intelligence. Previous studies have shown that people may conform to the expected attitudes and behav- ior of the avatar they are represented by, without necessar- Methods ily being aware of that (i.e., the Proteus effect; e.g., Yee & Bailenson, 2007; Yee, Bailenson, & Ducheneaut, 2009; Participants Peña, Hancock, & Merola, 2009). For instance, participants have been found to behave more confidentially and friendlier Given the unpredictable effect sizes, the sample was cho- with strangers or to behave more aggressively during a nego- sen to double our lab standard for novel manipulations (20/ tiation when controlling attractive and tall avatars, respec- group; see Simmons, Nelson & Simonsohn, 2011). 52 vol- tively (Yee & Bailenson, 2007; see also Yee, Bailenson, & unteers participated in the study for course credit or pay but Ducheneaut, 2009). Similarly, it has been found that partici- 12 of them were excluded due to technical problems—thus pants represented by avatars dressed in Ku Klux Klan outfits leaving 40 participants (mean age 20.88 years, SD = 2.83 reported more negative and aggressive thoughts than those years, range 18–29 years; seven males). We used the depart- dressed as doctors (Peña et al., 2009). Taken together, these ment’s standard advertisement system and accepted all par- findings are consistent with previous literature showing that ticipants registering in the first (and only) wave. Written trait concepts and stereotypes become active automatically informed consent was obtained from all participants before in the presence of relevant behavior or stereotyped-group the experiment. Participants were naive as to the purposes of features (i.e., through perception), and can cause people to the experiment. The study conformed to the ethical standards behave consistently with the activated stereotypes (Char- of the declaration of Helsinki and the protocol was approved trand & Bargh, 1999). Therefore, considering the common by the local research ethics committee. stereotype that humans are more intelligent than non-human animals, we predicted that enfacing and, thus, in some sense Experimental setup becoming an ape should reduce intelligence and result in a lower score in the SPM test. Note that we relied on, but did Figure 1 shows the basic setup. The virtual faces were con- not directly test this stereotype in our participants because structed and controlled by means of virtual reality environ- the assessment would have primed the respective stereotype ment software (Vizard and FAAST; Suma et al., 2013). We 1 3 376 Psychological Research (2019) 83:373–383 Fig. 1 The experimental setup. The participant’s facial move- the Kinect system, which requires a minimum distance of 1.8  m to ments were monitored by means of a Kinect system (recording recognize human movements. Participants (here the first author) frame rate = 30  Hz) and an Intersense orientation tracker (update wore a cap with an orientation tracker attached on it (see right yel- rate = 180 Hz). The Kinect system (see upper left yellow frame) was low frame). Computer tasks (i.e., the emotion rating and the Raven’s located behind and above the computer screen showing the virtual Standard Progressive Matrices tasks) were presented on a second face (see lower left yellow frame). Participants sat at about 2 m from screen located next to the screen showing the virtual face used Vizard to build three three-dimensional virtual faces, where the ape face on the screen was”) is a location-related one for each gender, based on average Caucasian faces (e.g., ownership item that is sometimes aggregated with direct Jones et al., 2006) and one for the ape face. A computer- ownership to assess perceived ownership properly (Kalck- ized morphing procedure was used to gradually merge the ert & Ehrsson, 2014), Q3 (“It seemed like my own face human and the ape faces (see Fig. 2). By integrating Kinect, began to resemble the ape face on the screen”) assesses Intersense, FAAST, and Vizard, our setup allowed partici- perceived appearance similarity, a possible correlate of pants to freely move or rotate their own face to control the ownership (Tajadura-Jiménez et  al., 2012), and Q4 (“I movement or rotation of the virtual face, with a latency of could control the ape face”) perceived agency, which about 40 ms—a value far below the 300-ms threshold pro- according to Ma and Hommel (2015b) predict ownership posed by Shimada, Fukuda, and Hiraki (2009) as the critical in participant-active setups. For each item, participants time window allowing for the occurrence of multi-sensory chose a score on a Likert scale ranging from 1 (“strongly integration processes constituting self-body representation. disagree”) to 7 (“strongly agree”). Note that we did not use the “control” questions of the RHI questionnaire, as in our Measures previous studies (Ma & Hommel, 2015a, 2015b) we found evidence suggesting that, for illusions created using VR, Enfacement questionnaire synchrony is likely to affect responses to control questions as well. This is likely because dynamic manipulations, Four items were adopted from the standard RHI question- compared to the static ones, can make all self-perception naire (Botvinick & Cohen, 1998) and enfacement studies aspects perceivable or salient, thereby producing measur- (Tajadura-Jiménez, Grehl, S., & Tsakiris, 2012; Sforza able synchrony effects on all items relating to any aspect et al., 2010). Q1 (“I felt the ape face was my own face”) of self-perception that can correlate with ownership and directly addresses perceived ownership, Q2 (“It seemed agency (cf., Ma & Hommel, 2015b). like I was sensing the movement of my face in the location 1 3 Psychological Research (2019) 83:373–383 377 Fig. 2 Some representative images resulting from the morphing 25% ape, 50% human and 50% ape, 25% human and 75% ape, and procedure applied to male (upper panel) and female (lower panel) 0% human and 100% ape. The resulting 100% ape face was identical faces. From left to right, 100% human and 0% ape, 75% human and regardless of whether the male or the female face was morphed (Epstein, 1984; Demoulin et al., 2004), 6 primary (affec- Including others in the self (IOS) scale tion, pleasure, attraction, fear, exhaustion, and pain) and 6 secondary emotions (admiration, hope, surprise, embar- A variant of the IOS scale (Aron, Aron, & Smollan, 1992) assessed subjective aspects of self–other integration. The rassment, contempt, humiliation). Each participant per- formed two task blocks, one in which emotions were rated scale consists of seven Venn diagram-like pairs of circles representing varying degrees of self–other overlap (i.e., sub- for Human and one in which they were rated for Ape. The order of the two blocks was counterbalanced across partici- jective self–other integration). Participants are to choose the overlap that they think represents best the degree to which pants, and within each block emotions were presented in a random order. the virtual face looks like their own, how familiar it feels to them. Procedure Raven’s standard progressive matrices (SPM) After having read and signed the informed consent, partici- SPMs (Raven, 1938) assessed participants’ fluid intelli- pants were seated in front of a computer monitor and to wear the cap (as shown in Fig. 1). Each participant underwent two gence. The test consists of 60 trials of increasing difficulty. Participants either received the even 30 trials on the first synchrony (synchronous and the asynchronous) conditions in counterbalanced order. During both synchrony conditions, experimental condition and the odd 30 trials on the sec- ond experimental condition or vice versa (counterbalanced the participants actively operated the virtual face for 3 min by freely displacing or rotating their own face, which led across participants). to corresponding displacement or rotation movements of the virtual face. The 3-min interval was divided into three Emotion rating task parts. During the first 30 s, participants were presented with either the male or the female virtual face (depending on their The emotion rating task was adopted from De Dreu et al. (2011). Participants were asked to rate, on a Likert scale gender), which was 100% human. Then, for the next 120 s, the human face was morphed into the ape face (from 100% ranging from 1 (not at all) to 7 (very much), how much humans and apes are able to experience 12 emotions human–0% ape to 0% human–100% ape, in steps of 0.83% 1 3 378 Psychological Research (2019) 83:373–383 every second, for a total of 120 morphs, plus the two cor- Results responding mapped texture pictures, each for male or female participants; see Fig. 2 for representative images resulting Enfacement questionnaire from the morphing procedure). For the remaining 30 s, the viewed face was 100% ape. Shapiro–Wilk test revealed that the distribution of the dif- The only difference between the two conditions per- ferences deviated significantly from the normal distribution tained to the temporal delay between people’s own move- for Q2, Q3 and Q4 (p ≤ 0.04), but not for Q1 (p = 0.06). ments and that of the virtual face, which—excluding the Because the data were not normally distributed for three out 40-ms time delay caused by the equipment—was either of four questionnaire items, the non-parametric Wilcoxon 0 s (= synchronous) or 3 s (= asynchronous). Immediately signed-rank test was used to compare ratings across the two after each synchrony condition, participants answered the synchrony conditions. For non-symmetrically shaped distri- enfacement questionnaire, responded to the IOS scale, per- butions values resulting from the non-parametric sign test formed the emotion rating and eventually the Raven task. We are reported. Analyses showed that synchrony was signifi- preferred not to counterbalance the order of the Raven and cant for all items (Q1: Z = − 3.85, p < 0.001, r = 0.61; Q2: the emotion rating tasks for the following reason. Research Z = − 4.50, p < 0.001, r = 0.71; Q3: Z = − 3.47, p < 0.001, has shown that performing a demanding cognitive task is r = 0.55; Q4: Z = − 4.53, p < 0.001, r = 0.72), with par tici- likely to reduce self-control (i.e., it can cause ego-depletion; pants experiencing more ownership, similarity, and agency Baumeister, Bratslavsky, Muraven, & Tice, 1998), and evi- in the synchronous than in the asynchronous condition. dence exists that lack of self-control can affect interpersonal Hence, we successfully induced a virtual enfacement illu- perception (e.g., Vohs & Ciarocco, 2004; Govorun, & Payne, sion for the ape face. Table 1 provides participants’ ratings 2006). Therefore, to avoid possible confounding effects (i.e., median and range in parentheses) separately for each resulting from ego-depletion we preferred to have partici- item and for the aggregated ownership items (Q1–Q2) as a pants perform the most demanding task (i.e., the Raven task) function of synchrony condition. after the emotion ratings task. All participants were asked to take a 5-min break between the two synchrony conditions. IOS Shapiro–Wilk test revealed that the distribution of the dif- ferences deviated significantly from the normal distribution (p = 0.002). A Wilcoxon signed-rank test showed that the synchrony effect was significant, indicating that participants Table 1 Overview of Measure Experiment Replication participants’ performance for all dependent measures as a Synchrony Asynchrony Synchrony Asynchrony function of synchrony Enfacement questionnaire (median and range)  Direct ownership (Q1) 4.0 (6) 2.0 (6) 3.0 (5) 2.0 (6)  Location (Q2) 5.5 (6) 3.0 (6) 5.0 (6) 2.0 (5)  Aggregated ownership (Q1-Q2) 4.5 (6) 2.75 (6) 4.0 (5) 2.5 (5.5)  Similarity (Q3) 3.0 (6) 2.0 (5) 2.0 (6) 2.0 (5)  Agency (Q4) 6.0 (6) 4.0 (6) 6.5 (6) 4.5 (6) IOS (median and range) 4.5 (6) 3.0 (6) 4.0 (5) 3.0 (5) Raven (median and range) 25.0 (13) 26.0 (12) 25.0 (9) 26.0 (10) Emotion rating (mean and standard error of the mean) ns  Human (primary) 6.63 (0.07) 6.65 (0.06) 6.71 (0.07) 6.69 (0.08) ns  Human (secondary) 6.58 (0.08) 6.63 (0.09) 6.48 (0.12) 6.55 (0.11)  Ape (primary) 6.07 (0.10) 5.95 (0.11) 5.71 (0.14) 5.36 (0.22)  Ape (secondary) 4.78 (0.19) 4.50 (0.22) 4.33 (0.19) 3.89 (0.24) Median values and range (in parentheses) are reported for the enfacement questionnaire items, IOS and Raven, whereas means and standard error of the mean (in parentheses) are reported for the emotion rating task. Significant and non-significant synchrony effects are indicated by “ ” and “ns”, respectively. Columns 2 and 3 show results for the original experiment, and columns 4 and 5 for the replication 1 3 Psychological Research (2019) 83:373–383 379 experienced greater overlap with the virtual face after the syn- Replication chronous than after the asynchronous condition, Z = − 4.45, p < 0.001, r = 0.70, see Table 1. While the findings came out as expected, some of the effects were rather small numerically and just reached the significance SPM level. To make sure that our conclusions are not based on spu- rious, non-reproducible findings, we conducted an exact repli- Shapiro–Wilk test revealed that the distribution of the dif- cation study. 40 new participants were tested, and the statistical ferences deviated significantly from the normal distribution findings were exactly as in the first experiment: the synchrony (p = 0.043). A sign test showed that the synchrony effect was effect was significant for all enfacement questionnaire items significant, with a significant median decrease in Raven scores (Q1: Z = − 2.35, p = 0.02, r = 0.37; Q2: Z = − 5.13, p < 0.001, after the synchronous condition, compared to the asynchro- r = 0.81; Q3: Z = − 2.62, p = 0.01, r = 0.41; Q4: Z = − 3.85, nous one, Z = − 2.03, p = 0.043, r = 0.32, see Table 1. p < 0.001, r = 0.61), IOS ratings, Z = − 3.40, p < 0.001, r = 0.54, Raven scores, Z = − 2.34, p = 0.02, r = 0.37, and a significant Emotion ratings two-way interaction involving the factors synchrony and spe- cies was found for the emotion rating task, F(1,39) = 9.46, Shapiro–Wilk test indicated that residuals were not normally p = 0.004, ηp2 = 0.20, with synchronicity affecting emotion distributed for the majority of factor level combinations ratings when judging apes but not when judging humans (see (p < 0.05). However, due to the central limit theorem, the Table 1). ANOVA can be considered robust to violations of normal- ity (Glass, Peckham & Sanders, 1972; Harwell, Rubinstein, Correlations Hayes & Olds, 1992; Schmider, Ziegler, Danay, Beyer, & Bühner, 2010). Therefore, ratings were analyzed by means Next, we combined the data of the two experiments to assess of a repeated-measure ANOVA with synchrony (synchro- the relationship between perceived ownership and ownership- nous vs. asynchronous), species (human vs. ape) and emo- related characteristics (self–other similarity and agency), and tion type (primary vs. secondary) as within-participant fac- between these factors and task (emotion ratings for Ape and tors. ANOVA revealed significant main effects of emotion Raven) performance. The degrees of ownership (as assessed type, F(1,39) = 65.39, p < 0.001, ηp2 = 0.63, and species, by the aggregation of Q1–2), agency (Q4), and self–other simi- F(1,39) = 86.27, p < 0.001, ηp2 = 0.69: ratings were higher larity (IOS ratings) were computed by subtracting asynchro- for primary than for secondary emotions (6.3 vs. 5.6) and, as nous ratings from synchronous ratings. Likewise, synchrony- expected, for humans than for apes (6.6 vs. 5.3). Moreover, a induced changes in task performance were computed by significant interaction involving the factor species and emo- subtracting emotion ratings for Ape and Raven scores observed tion type was found, F(1,39) = 71.07, p < 0.001, ηp2 = 0.65. after the asynchronous condition from those observed after Consistent with previous findings (Epstein, 1984; Demoulin the synchronous condition. We computed one-tailed Spearman et al., 2004), Bonferroni post hoc tests revealed that partici- correlations among changes in ownership, agency and IOS pants judged apes to be able to feel primary emotions to a ratings, and synchrony-induced changes in task performance. greater extent than secondary emotions (6.0 vs. 4.6, p < 0.001), Significant and positive correlations were observed between whereas no difference between primary and secondary emo- ownership and IOS changes, rho = 0.45, p < 0.001, ownership tions was found when rating human emotions (6.6 vs. 6.6, and agency changes, rho = 0.24, p = 0.017, and between agency p = 1). More importantly, the interaction between synchrony and IOS changes, rho = 0.41, p < 0.001. Interestingly, emotion and species was also significant, F (1,39) = 6.22, p = 0.017, rating changes correlated positively with agency, rho = 0.40, ηp2 = 0.14. Bonferroni post hoc tests confirmed that par- p < 0.001, and IOS changes, rho = 0.29, p = 0.004, and nega- ticipants attributed to apes a higher capacity to feel emo- tively with Raven changes, r = − 0.26, p = 0.010. No other sig- tions in the synchronous than in the asynchronous condition nificant correlations were found, absolute rho values ≤ 0.09, (p = 0.03), whereas no difference between the two synchrony ps ≥ 0.22. conditions was observed when rating human emotions (p = 1; see Table 1). No other significant sources of variance were observed, F ≤ 2.78, p ≥ 0.10. Discussion s s This study set out to test whether embodiment can be dem- onstrated across species and whether this would induce self–other assimilation (and feature migration) in terms of intelligence and emotion attribution—as implied by our 1 3 380 Psychological Research (2019) 83:373–383 application of TEC (Hommel et al., 2001). The first ques- demonstration of feature migration in the sense of Ma et al. tion can be answered ar ffi matively: when the ape face moved (2016): increasing the overlap of self- and other-represen- in synchrony with the participants’ own face, they were tation invites illusionary conjunctions, in which features of more likely to perceive ownership for the former. It is true the other become features of oneself. Moreover, enfacing an that ownership perception was not perfect, as the score fell ape tempted participants to attribute more emotions to apes, into the midrange of the scale—a finding that is consistent another case of feature migration: when becoming more like with other studies of the virtual-hand (e.g., Ma & Hommel, an ape, participants took their emotional capabilities with 2015a, 2015b) and the virtual-face illusion (Ma et al., 2016; them, so to speak. Note that synchrony affected primary and Tajadura-Jiménez et al., 2012; Sforza et al., 2010). This limi- secondary emotions alike. While primary emotions are con- tation notwithstanding, the fact that a short practice over 3 sidered to be shared among humans and other highly evolved min was sufficient to affect one’s identification with another animals, secondary emotions are commonly thought to be species—which most participants were likely to have little uniquely human (Epstein, 1984). If our human participants experience with—must be considered notable. Converging would have judged apes from their human perspective, one evidence supporting the conclusion that our participants might have expected that synchrony has a stronger impact identified with the virtual ape comes from the IOS ratings, on primary emotions attributed to apes than on secondary which confirm that synchrony increased the perceived over - emotions. However, given that synchrony enhanced the attri- lap between participant and ape. Hence, humans are able bution of both kinds of emotions, it seems that the emotion to identify with a member of another species, probably in a attribution in this condition relied on a more “insider per- similar way as they can embody the hand or face of another spective”, that is, from the perspective of an ape feeling like human. This result is not unanticipated as it fits with previ- a human. In other words, when embodying another person ous claims that people’s self-construal is dynamic and sensi- (or a member of another species), self-related attributes can tive to situational and cultural biases (Colzato et al., 2012; be extended to the embodied others who become more like Kühnen & Oyserman, 2002), and that people are rather the self. This fits with the observation that synchrony had flexible regarding which objects and events they consider no effect on the attribution of emotions to humans, which as being part of their body—as long as they can control also rules out the possibility that the enfacement experience the behavior of these objects and events (Ahn et al., 2016; facilitated emotion attribution in general. Kilteni et al., 2016; Ma & Hommel, 2015a, b; Piryankova In the present study, we were interested to see whether et al., 2014; Steptoe et al., 2013; Kilteni et al., 2012; van feature migration can lead to the integration of features der Hoort et al., 2011). It is worth noting that, in the present of another individual into the representation of oneself. study, to maximize the chance of eliciting a virtual enface- However, we would like to emphasize that, theoretically ment illusion of an ape face, we made use of a morphing speaking, features would be expected to migrate both procedure in which a synchronously or asynchronously mov- ways: from other to self and from self to other. So, while ing virtual human face slowly morphed into an ape face. As our present study was tapping into the route from other to mentioned in the Introduction, such a choice was aimed at self, some recent studies have provided evidence that fea- counteracting possible feelings of irritation and strangeness tures may migrate from self to other as well. For instance, that could have arisen by confronting participants directly body-ownership illusions have been found to induce a more with the face of a member of another species. It remains to positive attitude toward social out-groups (e.g., Maister be established whether the morphing procedure was really et al., 2015), which from our theoretical view might sug- necessary for the illusion to occur, or whether virtual enface- gest that a positive self-image can migrate to an embod- ment of a member of a different species can also be obtained ied other. Indeed, considering that attributing emotions to without such a procedure. outgroup members represents an attitude, our findings are The second most important question can also be answered consistent with, and can be seen as an extension of previous affirmatively: both the intelligence measure and the emotion outgroup studies along the lines of Maister et al. (2015). attributions were affected by synchrony. As predicted from As already mentioned, synchronous stimulation of partici- our TEC-based approach, perceiving oneself to own an ape pants’ own hand and a rubber hand typical for a racial out- face made people behave less intelligently; that is, partici- group member increased perceived ownership for the rub- pants tended to adopt the intellectual characteristics humans ber hand and induced a more positive attitude toward that attribute to the species they perceived themselves to become outgroup (Farmer et al., 2013). Similarly, Inzlicht, Gutsell, a part of, thereby confirming previous findings document - and Legault (2012) reported that negative attitudes toward ing people’s tendency to adopt attitudes and behavior of the a racial outgroup were reduced by synchronizing one’s own avatar they are represented by (i.e., the Proteus effect; e.g., movements with those of an outgroup member. It is true Yee & Bailenson, 2007; Yee, Bailenson, & Ducheneaut, that such a modulation of implicit racial attitudes has not 2009; Peña, Hancock, & Merola, 2009). We consider this a been observed in a recent study using a static enfacement 1 3 Psychological Research (2019) 83:373–383 381 paradigm (Estudillo & Bindemann, 2016). This suggests et  al. (2013) and Inzlicht et  al. (2012). Notwithstanding that embodiment illusions are not always effective in biasing these interesting open questions, our findings provide fur - self- and/or other-perception, especially when concerning ther evidence that the boundaries between perceived self and body parts that are strongly tied to the self-identity, just like perceived other are rather flexible, and that representational faces. However, recent comparisons between dynamic and self–other overlap invites illusory conjunctions of features static hand illusion conditions have revealed that dynamic from one representation to the other—including others of conditions, as used in the present study, are much more sen- another species. sitive to manipulations and strongly increase the coherence Acknowledgements The research was supported by a post-graduate between dependent measures (Ma & Hommel, 2015a, b). It scholarship of the China Scholarship Council (CSC) to KM, and an is thus possible that dynamic conditions, perhaps together infrastructure grant of the Netherlands Research Organization (NWO) with the morphing technique we used in the present study, to BH. will be more successful in demonstrating modifications of racial attitudes. Author contributions The study is based on the idea of KM, who also developed the technical design of the study, collected and analyzed Note that in the present study we relied on explicit meas- the data, and prepared the first draft. RS and BH contributed to the ures but did not use implicit measures of ownership, a deci- development of the study concept and to the analysis and interpretation sion we made for two reasons. First, explicit and implicit of the data, and they provided critical revisions. All authors approved measures of body ownership have often been demonstrated the final version of the manuscript. to dissociate (e.g., Liepelt, Dolk & Hommel, 2017; Ma & Hommel, 2015a, b). This implies that explicit and implicit Compliance with ethical standards measures rely on different kinds of information, and so far, Conflict of interest The authors declare that they had no conflicts of in- no theoretical account for such dissociations has been sug- terest with respect to their authorship or the publication of this article. gested. This renders it unclear what kind of information implicit measures would add and which theoretical implica- Ethical standards All procedures performed were in accordance with the ethical standards of the institutional research committee and with tions the convergence or divergence with explicit measures the 1964 Helsinki declaration and its later amendments. would have. Second, the inclusion of implicit measures was unlikely to be successful in our study. Previous face-owner- ship studies have used self–other discrimination or recogni- Open Access This article is distributed under the terms of the Crea- tive Commons Attribution 4.0 International License (http://creat iveco tion of self–other morphed faces (e.g., Sforza et al., 2010; mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- Tsakiris, 2008; Tajadura-Jiménez et al., 2012) as an implicit tion, and reproduction in any medium, provided you give appropriate measure. The typical outcome was the tendency of partici- credit to the original author(s) and the source, provide a link to the pants to under-discriminate between pictures of oneself and Creative Commons license, and indicate if changes were made. of a very similar human other in the synchrony, compared to the asynchrony condition. This bias is commonly very small (around 5%), which renders it extremely unlikely to References get anything measurable when comparing oneself against the picture of an ape. 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Published: Jul 2, 2018

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