The Neural Control of Vision
E. The Striate Cortex

Figure 11 shows schematically the responses of a V1 cell to bars of light moving across its receptive field in various orientations and directions. The curve so generated reveals the tuning function for the cell. The cell responds most vigorously when the bar is horizontal and moves downward across the receptive field; the response declines as the orientation of the bar deviates progressively from the horizonal. There is no repose to the bar when it is horizontal and moves upward. Thus this cell reveals two of the transforms noted above: orientation and direction selectivity, an attibute seen in the majority of V1 cells.