Atypical Integration of Motion Signals in Autism

Abstract

Numerous studies have reported a deficit in coherent motion perception in autism spectrum conditions (ASC). Research on motion perception has identified a neural circuit in which primary motion signals represented in middle-temporal area (MT) are integrated in the banks of the lateral-intraparietal sulcus (LIP) over time towards a decision-bound. According to this model, a deficit in global motion perception should be more strongly manifest with shorter than longer stimulus durations. 36 participants (19 ASC) performed a forced-choice motion discrimination task, manually indicating the global direction of motion (left/right) of a field of dots. Stimulus duration varied between blocks (200/400/1500 ms). Coherence level (4–75%) and dot direction were randomly chosen on each trial. Coherent motion perception thresholds were significantly higher in the ASC group (p < 0.05) only at the shortest duration (200 ms). ASC and control performance at the longer durations were identical. To investigate the neural substrate of this behavioral deficit, an additional 18 participants (10 ASC) also performed an event-related fMRI version of the motion coherence task. Overall there was a reduction in the activation of the autistic MT across all coherence levels, but critically, this reduction was greater at the shorter stimulus durations. This reduction may lead to worse performance by slowing the formation of a decision variable and reducing its reliability. In conclusion, we report a robust behavioral deficit in coherent motion perception in ASC when sensory integration time is limited. This impairment is absent at longer stimulus durations. These results point to atypical accumulation of motion signals in ASC: individuals with ASC require more evidence to reach a decision threshold than controls. Further, we have shown that this atypical accumulation is reflected in reduced activation of the autistic MT. This result may provide insight into higher-order cognitive and social deficits that rely on visual integration, such as joint attention.

NIMH Intramural Research Program, Gates-Cambridge Trust, NIH-Cambridge Fellowship.