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Autism spectrum disorders (ASD) are part of neurodevelopmental disorders and are characterized by deficits in social communication and interaction. A basis for interpretation of social contexts is the perception of visual information. Especially the processing of movement is of essential meaning. Studies of visual perception in individuals with ASD showed a deficit in perception of coherent motion. The processing of movement is located in the dorsal pathway of the visual system (MT/V5). The fact that individuals with ASD showed a higher threshold in detecting coherent motion resulted in the theory of a dorsal stream deficit. The investigation of this theory on neurophysiological level, mostly by fMRI, led to inconsistent findings. Thus, a further possibility of examining neurophysiological processes, especially temporal dynamics, are event-related potentials (ERP). ERP reflect higher processing in the cortex and N200 is the dominant potential in coherent motion. A deficit in the dorsal pathway therefore should result in a reduced activity and thus a reduced amplitude of N200.
In this study the participants were presented a “random dot kinematogram” (RDK) while being examined with a 64-chanel-eeg. The target consisted of a cloud of randomly moving dots from which a fraction of the dots moved coherently (dependant on the level of coherence, 20%, 40% or 60%) to the left or right side. The subjects were asked to detect the direction of the movement. Behavioral data and EEG-data were collected. After filtering the eeg-data was averaged in a pre-determined epoch and selected electrodes. The analysis contained 12 children and adolescents with ASD and 12 typically developing controls.
The coherently moving dots elicited a N200 followed by a late positive potential (P400). The group comparison showed a significant difference in amplitude of N200: individuals with ASD showed a reduced N200. Latency of N200 did not differ between the groups. There were no differences in amplitude or latency for P400. On behavioral level no significant group levels emerged.
The study demonstrated a difference in processing of coherent motion on neurophysiological level. The reduced N200 indicates a different processing in early parts of the dorsal visual pathway. In the context of development of visual processing in infancy and impairments in visual processing in other developmental disorders the results support the theory of dorsal stream deficit in ASD.
The study made a contribution to explaining neurophysiological basics of coherent motion processing in ASD.