Blocking facial mimicry reduces perceptual sensitivity for facial expressions
63.4069, Wednesday, 20-May, 8:30 am - 12:30 pm, Pavilion
Alberta Ipser1, Richard Cook1; 1Department of Psychology, City University London
Built on models of ‘action understanding’, motor theories of expression perception propose that facial simulation, a process similar to covert imitation, aids perception and interpretation of others’ facial expressions. As predicted by these accounts, some reports suggest that blocking facial mimicry impairs expression recognition. However, these reports have been criticized and motor theories remain controversial. Crucially, it remains to be determined whether the labeling errors observed reflect a loss of perceptual sensitivity - a genuine perceptual phenomenon - or whether they are a product of response bias. The current study addressed this question using a novel psychophysical paradigm, where observers judged whether smiles drawn from a morph continuum were sincere or insincere. In Experiment 1, we confirmed that cues from both the eye and mouth regions contribute to sincerity judgments. Experiment 2 measured discrimination of smile sincerity across free-viewing and blocked-mimicry conditions. In the blocked-mimicry condition, participants pronounced vowel sounds during stimulus presentation, thereby loading the motor system and preventing mimicry. Each participant’s responses were modeled by fitting psychometric functions. Sensitivity to changes in smile sincerity and bias were inferred from the slope and the point of subjective equality (PSE), respectively. Motor interference significantly decreased sensitivity relative to baseline, but did systematically affect bias. Experiment 3 examined whether the motor manipulation has similar effects on judgments of facial gender, a task equated for difficulty but which is not thought to recruit motor processes. Neither slope nor PSE estimates for gender judgments were affected, indicating that the loss of sensitivity seen in Experiment 2 is relatively specific to judgments of expression and does not reflect generic distraction. These findings accord with the view that judgments of facial expression benefit from motor contributions to perception.