To the Editor: Ami Klin, Ph.D., et al. (1) showed that a high-functioning autistic adult looked at mouths rather than at the eyes of adults’ faces when viewing naturalistic social situations, while a normal comparison adult showed the opposite pattern. According to this argument and others, the authors argued that low orientation to salient social cues embedded in naturalistic situations is a core deficit in autism.

In their Letter to the Editor, Chantal Kemner, Ph.D., and Herman van Engeland, Ph.D., M.D. (2), wrote that when autistic children are shown a static presentation of faces, they do not reach the conclusion of Dr. Klin et al. They argued that the discrepancy between these results is due to a difference in the presentation of facial stimuli, i.e., the dynamic presentation in the study of Dr. Klin et al. versus the static presentation in their own study.

We confirm that low-functioning autistic children are impaired in the processing of physical environmental movement, particularly rapid movement (3), while high-functioning autistic children are much less impaired in the same type of tasks. When biological movement is concerned, autistic children perform relatively adequately in emotional and nonemotional expression-recognition tasks when facial expressions are displayed slowly on video (4). Along the same line, low-functioning autistic children better recognize dynamic facial expressions when displayed slowly than when presented at normal speed. Considering these arguments and others, we proposed the rapid visual-motion integration deficit hypothesis in autism (5). According to this hypothesis, some autistic individuals having major movement-processing disorders from early in their lives will avoid rapid physical and biological movements (considered as aversive stimuli), thus disrupting secondarily social interaction. Some of these individuals, or some autistic persons having minor motion-processing disorders, will search for, habituate themselves to, and learn to handle and cope with such kinds of stimuli. To summarize, rapid visual-motion processing deficits constitute a core neuropsychological marker of autism and secondarily account for the deficit in social interaction.

Thus, when the autistic subject focuses on the mouths of adults’ faces in the study by Dr. Klin et al., he or she probably attempts to capture facial speech information that is difficult to process accurately and efficiently in naturalistic social situations while avoiding looking at the fastest facial movements (i.e., saccadic eye movements).

Therefore, discrepancies between the results of Dr. Klin et al. and of Drs. Kemner and van Engeland might be due to the severity of autism in the subjects tested in their respective studies and to the kind of presentation of facial stimuli.