NONLINEAR RESPONSES OF SIMPLE CELLS TO MACH BAND STIMULI - EVIDENCE FROM EARLY MONOCULARLY DEPRIVED CATS

We have previously shown that, cat simple cells respond linearly to ed ges of variable blur widths: cells with receptive fields (RFs) of even symmetry respond better to a luminance ramp (where Mach bands are obs erved); cells with RFs of odd symmetry respond better to a luminance s tep (where no Mach bands are perceived). Our evidence has also indicat ed the existence of inhibitory interaction between cells with RFs of e ven and odd symmetry as predicted by the Tolhurst-Ratliff Mach band mo del. Since monocular deprivation is known to impair cortical inhibitor y mechanisms, we studied the responses of simple cells of adult cats m onocularly deprived at the age of 8-10 weeks to Mach band stimuli in o rder to delineate specific changes in inhibitory interactions caused b y monocular deprivation. In pattern-deprived cats, particularly for ce lls driven by the deprived eye, there were many cells that responded c ontrary to linear models: odd-symmetric cells responded maximally to b lurred edges while even-symmetric cells responded maximally to sharp e dges. Cells that responded maximally as predicted, responded, similarl y to nor mal cat cells, less than expected at suboptimal widths. All c ells in normal and light-deprived cats responded in a linear fashion t o sinusoidal stimuli. We conclude, therefore, that intracortical inhib ition shapes simple cells' responses to edges. Monocular deprivation i mpairs this mechanism, thus causing simple cells in monocularly depriv ed cats to respond nonlinearly to edges. All simple cells responded li nearly to gratings since it is not the linear spatiotemporal RF of the se simple cells that was impaired under monocular deprivation.