Phase of responses to sinusoidal gratings of simple cells in cat striate cortex.

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Abstract
The phase of responses evoked in simple cells of cat striate cortex by moving sinusoidal gratings was determined. The technique used avoided bias due to subjective estimation of receptive-field location. In most simple cells there was a locus in the receptive field at which the phase of the response peaks remained constant, irrespective of spatial frequency and movement direction. These simple cells fell into 2 groups, responding half a cycle out of phase with one another. At low velocities of grating movement, the peak response occurred before the maximum or minimum grating luminance crossed the response locus. At higher velocities, response phase was later largely because of response latency. The 2 groups of simple cells corresponded closely in response phase to on- and off-center cells at lower levels in the visual pathway, provided an appropriate correction for latency was made. This is consistent with most simple cells receiving input from mainly on- or off-center afferents. Bar and edge responses could be predicted from the responses to gratings. As in lower level cells, the phase of simple-cell responses relative to a fixed reference point in the visual field may be described by a simple linear function, thus fixing the responses of each cell into a spatiotemporal coordinate system, which may be of value for analysis of visual stimuli.