SPACE-TIME SPECTRA OF COMPLEX CELL FILTERS IN THE MACAQUE MONKEY - A COMPARISON OF RESULTS OBTAINED WITH PSEUDOWHITE NOISE AND GRATING STIMULI

White noise stimuli were used to estimate second-order kernels for com plex cells in cortical area V1 of the macaque monkey, and drifting gra ting stimuli were presented to the same sample of neurons to obtain or ientation and spatial-frequency tuning curves. Using these data, we qu antified how well second-order kernels predict the normalized tuning o f the average response of complex cells to drifting gratings. The esti mated second-order kernel of each complex cell was transformed into an interaction function defined over all spatial and temporal lags witho ut regard to absolute position or delay. The Fourier transform of each interaction function was then computed to obtain an interaction spect rum. For a cell that is well modeled by a second-order system, the cel l's interaction spectrum is proportional to the tuning of its average spike rate to drifting gratings. This result was used to obtain spatia l-frequency and orientation tuning predictions for each cell based on its second-order kernel. From the spatial-frequency and orientation tu ning curves, we computed peaks and bandwidths, and an index for direct ional selectivity. We found that the predictions derived from second-o rder kernels provide an accurate description of the change in the aver age spike rate of complex cells to single drifting sine-wave gratings. These findings are consistent with a model for complex cells that has a quadratic spectral energy operator at its core but are inconsistent with a spectral amplitude model.