Diversity of complex cell responses to even- and odd-symmetric luminance profiles in the visual cortex of the cat.

We have tested the hypothesis that complex cell receptive fields are made up of subfields which, for a given cell, have either exclusively even or exclusively odd symmetry. To do this we have measured the response of complex cells in the visual cortex of the cat to members of pairs of spatially limited even-symmetric stimuli (single light and dark bars) and pairs of odd-symmetric stimuli ("light-dark" and "dark-light" double bars) successively drifting across their receptive fields. The strength of a cell's response was estimated by measuring the sum of all spikes produced by a stimulus. Some complex cells respond about equally to single light and dark bars; others respond appreciably more to either the light or dark bar. The central tendency of average response histograms was estimated by measuring the mean with respect to position across the width of the receptive field. Many complex cells show distinct spatial offsets between the mean for narrow single light and that for dark bars as well as between means to double bars of opposite phase. Combined offset plots were constructed with the spatial offsets between means for single light bars and single dark bars along the x axis and the offsets between means to double bars of opposite phase along the y axis. There is significant scatter in the combined offset points; some falling at the origin, some at significant distances from the origin along the axes, and others well within each of the four quadrants. These diverse localizations in the offset plots rule out the simple models of complex cell spatial substructure described above and, therefore, imply considerable heterogeneity within the population of complex cells.