Perceptual Processing of Motion and Emotion in Low-Functioning Autism

Background: Whether persons with autism are affected by general visual peculiarities in movement processing or by selective peculiarities restricted to social stimuli is still a matter of debate. Recently, EEG responses to static emotional expressions tend to suggest abnormal cortical specialisation within social brain networks and increase activity of visual areas that disadvantage holistic facial processing. Meanwhile, visual areas are found to be normally sensitive to dynamic facial motion in typical and ASD groups. Put together, the above reported results stress the importance of a clear-cut distinction between processing emotion and processing motion.

Objectives: This study aimed at comparing in ASD and typical people the dynamical processing of physical, mechanical and biological stimuli and the scanning of regions of interests in human and robotic emotional expressions.

Methods: Twelve low-functioning adolescents with autism spectrum disorders (LFASD) diagnosed as such with DSMIV-R using ADI-R, 12 typically developing children (TD) matched on non-verbal developmental age, and 12 typical adolescents matched on chronological age (TA) participated in the study. The 36 participants were presented a novel morphing paradigm allowing a straightforward comparison of scores for dynamic changes in faces and in objects. The material was composed of 4 morphing videos of change of human emotional expression in face (happiness, sadness, surprise, fear), 4 morphing videos of change of the same emotional expressions displayed by a mechanical set-up, and 4 morphing videos of change of state in graspable objects (a plastic bottle, scissors, a safety peen, a pencil case) presented at a speed of 4000 ms with 101 frames. Participants had to recognize the target image among non target images. 

Results: Processing morphed stimuli, LFASD showed dissociation between performance for emotional expressions in faces and robotic set-up compared to graspable objects, while the TD and TA matched groups scored similarly for all three. Participants of each group were equipped with a eye-tracker in order to scan their exploration of the three kinds of stimuli. Here we focus on Regions of Interests (RoIs) and thus only include results concerning human versus robotic emotional expressions. For emotional faces, LFASD showed longer fixations to core emotional regions of interest (eyes and mouth) compared to the two typical groups. This however did not lead to a good performance in the processing of emotional faces. For robotic emotional patterns, ASD devoted significantly less attention to core emotional regions. Instead, they distributed equally their fixations between the two sources of motion: eyes and mouth on one hand and mechanical points on another hand. No such distribution was observed in the typical groups.  

Conclusions: Results are discussed in terms of a possible use by individuals with autism of the same strategy for emotion and object processing which would lead to lower their performance when the dynamics of facial expression is concerned. Taken together, these results suggest a local processing of facial movement rather than a processing of emotional signals in ASD people.