Reduced Perceptual Interactions Between Dynamic Facial Elements in Autism

Background: When neurotypical individuals view an upright face that repeatedly opens and closes its eyes, the presence of asynchronous mouth movements slows down the perceived velocity of the eyelids. However, when the same dynamic facial stimuli are viewed upside-down, this illusory slowing is greatly diminished. This illusion is thought to result from perceptual predictions about eye movements derived from the direction of mouth movements. The process of reconciling these predictions with veridical sensory signals, gives rise to the illusory slowing. The absence of the effect when faces are inverted indicates that dynamic cross-feature predictions are orientation-specific, and accords with the literature on ‘holistic’ or ‘configural’ representation of upright static faces.

Objectives: In light of suggestions that individuals with autism show reduced ability to i) derive perceptual predictions and ii) represent faces holistically, the present study sought to determine whether they also show reduced susceptibility to the illusory slowing of eyelid transitions induced by asynchronous mouth movements.

Methods: We compared the performance of a group of adults with autism (n=12) and a group of age, IQ and gender matched neurotypical controls (n=12) on a psychophysical procedure designed to measure the perceived duration of eye-opening and eye-closing transitions, when viewed with an accompanying mouth movement with a phase difference of 90°. Upright and inverted trials were randomly interleaved, and separate psychometric functions estimated for the two conditions.

Results: As expected, the neurotypical controls showed a highly significant inversion effect, whereby the perceived duration of the eyelid transitions was greater when viewed in the upright orientation, than when viewed upside-down. In contrast, the autism group showed no evidence of the illusion whatsoever; they perceived the transitions of the eyelids to be of equivalent duration when face stimuli were viewed upright and inverted.

Conclusions: The present findings add support to previous claims that individuals with autism show a significantly reduced tendency to represent upright faces holistically and thereby derive cross-feature predictions. Crucially, these findings extend previous reports with static faces, by demonstrating atypical whole-face processing of dynamic stimuli.