Key words: visual cortex, binocular vision, binocular disparity,
gain normalization, dichoptic masking, interocular masking
(Received 10 July 1997; accepted in final form 9 September 1997)
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When a cortical cell is activated by an optimal sinusoidal grating, its response can be attenuated by a superimposed second grating, oriented orthogonally to the optimal stimulus. This effect is known as cross-orientation suppression (COS). In previous work, monocular characteristics have been explored and interocular tests have been conducted in an attempt to locate the origin of the suppression. In this study, we have recorded extracellularly from cortical cells to investigate the binocular characteristics of COS. Our hypothesis is that binocular disparity influences the strength of the effect. Our results do not support this supposition. We find that binocular COS is as strong as monocular COS, but disparity changes are of no consequence. We also conducted interocular tests in which the optimal grating and the orthogonal mask were seen by separate eyes. Although most interocular effects were weak, they were present in almost every cell and spanned a wide range of suppression strengths. We also tested the effect of asynchronous presentation of optimal and orthogonal gratings. These temporal offsets did not affect the strength of COS. We conclude that the suppressive mechanism underlying COS is primarily monocular and acts prior to the convergence of the two monocular streams.