Abstract
Autistic tendency has often been associated with impaired visual motion sensitivity, global/local perception and visual discrimination of facial emotion. However, the neurophysiological mechanisms underlying this impaired visual perception have yet to be established. Nonlinear multifocal visual evoked potentials (Sutherland and Crewther, 2010) have demonstrated delayed magnocellular processing for high stimulus contrast in populations scoring high on Baron-Cohen’s autism spectrum quotient (AQ). Here we investigated the contrast response functions of the main peaks of the first order and first two slices of the second order multifocal VEP with (central unstructured patch subtending 4°) with temporal contrasts of 10%, 25%, 50%, 70% and 96% in 29 normal participants (8 High AQ, 12 Middle AQ, 9 Low AQ) showing no group differences in non-verbal IQ (Raven’s Advanced Progressive Matrices). Motion coherence sensitivity was also assessed. The contrast response function (CRF) for the first slice 2nd order (K2.1) showed high contrast gain and response saturation, while the second slice K2.2 showed lower contrast gain and little saturation – giving support for generation by the magno- and parvocellular systems respectively. As a function of participant AQ score, the High AQ group showed greater CRF amplitudes for the N60-P85 K2.1 response than Middle or Low AQ groups, while the CRFs for the N95-P125 K2.2 were similar across AQ groups. Tests of within-subject effects revealed a significant Contrast * AQ interaction between High and Low AQ groups. Also High AQ showed a significant delay in the K2.1 positivity at high contrast. An expected impairment in motion sensitivity was only observed in the High AQ group for limited lifetime low contrast (10%) coherent motion. The data suggest that the magnocellular system in High AQ individuals has more difficulty recovering after stimulation.
Meeting abstract presented at VSS 2012