Superior facial expression, but not identity recognition, in mirror-touch synesthesia

Abstract

Simulation models of expression recognition contend that to understand another's facial expressions, individuals map the perceived expression onto the same sensorimotor representations that are active during the experience of the perceived emotion. To investigate this view, the present study examines facial expression and identity recognition abilities in a rare group of participants who show facilitated sensorimotor simulation (mirror-touch synesthetes). Mirror-touch synesthetes experience touch on their own body when observing touch to another person. These experiences have been linked to heightened sensorimotor simulation in the shared-touch network (brain regions active during the passive observation and experience of touch). Mirror-touch synesthetes outperformed nonsynesthetic participants on measures of facial expression recognition, but not on control measures of face memory or facial identity perception. These findings imply a role for sensorimotor simulation processes in the recognition of facial affect, but not facial identity.

Figure 1.

Summary of tasks used. a, Films facial expression task. This task investigated participants' abilities to categorize the emotional expressions of others. Participants were presented with a target adjective describing an emotional state followed by three images shown consecutively for 500 ms each. Participants were asked which of the three images best portrayed the target emotion. In the actual task color stimuli were used. b, Cambridge face memory test. This task investigated participants' abilities to memorize facial identity. During the task, participants memorized six unfamiliar male faces. They were then tested on their ability to recognize the faces in a three-alternative-forced-choice paradigm. The Cambridge face memory test long form was used. This task is comprised of three sections from the original CFMT (shown in figure) and a fourth section involving 30 very difficult trials (for stimuli from the final section, see Russell et al., 2009). c, Cambridge face perception test. This task investigated participants' abilities to perceive faces while being less dependent on memory. Participants were shown a target face and six faces morphed between the target and a distractor face. Participants sorted the six faces by similarity to the target face. Faces were presented upright and inverted in a fixed pseudorandom order. d, Same–different expression-identity matching task. This task investigated participants' abilities to match another's facial identity or facial expressions. Participants were presented with a sample face followed by a fixation cross and then a target face. In the expression matching task, participants indicated whether the expression in the target face matched the expression in the sample face. In the identity matching task, participants indicated whether the identity of the target face and the sample face matched.

Figure 2.

Performance of mirror-touch synesthetes and nonsynesthetes on the films facial expression task (a), the CFMT+ (b), the Cambridge face perception test (c, d), expression matching (e), and identity matching (f). Mirror-touch synesthetes were significantly more accurate than nonsynesthetes at categorizing the emotional facial expressions of others (a). This was not found to be the case in tests of face memory. The performances of synesthetes did not significantly differ from nonsynesthetes on the CFMT+ (b). Nor were any significant differences found between the performance of synesthetes and controls on a measure of facial identity perception (c, d; note that superior performance is reflected in a lower error score in the Cambridge face perception test). There was, however, a significant task × group interaction when participants made same–different expression or identity judgments. Although we were unable to establish definitively the locus of this interaction, the finding does demonstrate a different profile of strengths across groups, which is consistent with the findings from our other tasks. On the expression task (e), there was a trend for synesthetes to outperform controls, whereas on the identity task (f), there was a trend for controls to outperform synesthetes. Within-group comparisons between the tasks revealed that controls were significantly more accurate in the identity compared with the expression task. Synesthetes did not show this bias toward identity matching; expression and identity matching performances were comparable; *p < 0.001.