Influence of stimulus width on directional bias in striate cortex.

Width summation of complex neurones in cat striate cortex was assessed for moving sine-wave gratings. Summation was restricted in special complex neurones, approximately matched receptive field width in intermediate complex neurones and exceeded it in most standard complex neurones. Responses to preferred and opposite directions of motion were compared: 12 of 20 complex neurones showed similar directional bias for moving sinewave gratings and for single moving bars of either contrast polarity; 8 of 20 were similarly or more weakly direction-selective for bars than for grating patches, dependent on patch width. In two of these, this was despite the fact that the directional bias for gratings was invariant with patch width. In the remaining six, differences could be accounted for by progressive increase or decrease in directional bias for gratings, as grating patch width was systematically increased. In conclusion, directional bias of a substantial proportion of complex cells is determined by stimulus configuration.