Evidence for nonlinear binocular interactions in human visual cortex.

Dichoptically presented uniform fields were sinusoidally modulated in luminance, with differing temporal frequencies between the eyes. This stimulus evokes a unique electrophysiological response termed "beats"; visual evoked potential (VEP) components reflecting nonlinear neural behavior and which could only arise from integrative binocular units. Individuals with strabismus or amblyopia, which accompany disrupted binocular function in the visual cortex manifest a severe reduction of this nonlinearity, suggesting an abnormality in the binocular cortical processes underlying this response.