THE NATURE OF THE INPUTS TO CORTICAL MOTION DETECTORS

Recently, Jagadeesh, Wheat and Ferster [(1993) Science, 262, 1901-1904 ] presented intracellular recordings from direction-selective simple c ells in primary visual cortex and provided an analysis to support the idea that synaptic summation in simple cells is linear. New analysis p resented in this study reveals that: (1) the number of subunits contri buting to the analyzed simple cell inputs is two; (2) the subunits are nonlinear in the time domain; (3) each subunit linearly integrates th e luminance across the receptive field being, thus, linear to local co ntrast; (4) the waveforms of the subunit signals are linearly modulate d by local contrast at the subunit loci unless the contrast changes it s sign; (5) the synaptic summation in the simple cell is linear; (6) n onlinearity of even harmonics has sufficient information for retrievin g of relative spatial phase of the subunits and reconstruction of the exact temporal profiles of the subunit signals.