Abnormal Attention in Autism Shown by Steady-State Visual Evoked Potentials

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Abstract
This study examined brain electrical responses as a physiological measure of speed and specificity of attentional shifting in eight adult males with autism. Subjects were required to shift attention between rapidly flashed targets alternating between left and right visual hemifields. When targets were separated by less than 700 ms, steady- state brain electrical response in both hemispheres was augmented and background EEG decreased for rightward shifts as compared with leftward shifts. At longer separations, persons with autism showed no modulation of background EEG, and high variability in steady-state response. These results contrast with those in normal controls, where in each hemisphere separately steady-state response increased and background EEG descreased for shifts directed contralaterally to that hemisphere. Group differences were significant at p < 0.04 for the steady-state response and p < 0.0001 for the background EEG. Lack of hemispherically independent modulation in autism may reflect the operation of a non-specific mechanism of sensory gating.