Responses of single units in cat visual cortex to moving bars of light as a function of bar length

Abstract

The responses of single units in the cat''s primary visual cortex to moving bars were examined quantitatively as a function of bar length. For about half the cells studied very long bars evoked weaker responses than short bars, implying that there were inhibitory regions flanking the receptive field center. In another quarter of the cell sample there was evidence of flanking regions which were facilitatory in effect. The strength of the flanking regions varied from cell to cell, and there was no sudden transition between cells which were hypercomplex and those which were not. Within the central region of the receptive field the responses of most (but not all) cells increased with bar length. About half the cells responded to very short bars or spots of light, but about 1 in 6 would not respond at all to short bars. Correlations were sought between the properties of cells as simple or complex, their responsiveness to moving spots of light, the size of their receptive field center, and the polarity, strength and size of their receptive field flanks. Simple and complex cells with small receptive fields were more likely to respond well to spots and have strong inhibitory flanks. Correlations were also sought between the above properties and several other parameters of cell behavior. Cells with strong inhibitory flanks were more broadly tuned for orientation. Individual cells were also more broadly tuned for the orientation of short bars than of long bars. Evidence was obtained that spatial summation can be linear or non-linear for different cells.