TEMPORAL DIVERSITY IN THE LATERAL GENICULATE-NUCLEUS OF CAT

Reverse correlation was used in conjunction with ternary white noise t o estimate the first-order spatiotemporal receptive-field structure of LGN cells in the anesthetized, paralyzed cat. Based on a singular-val ue decomposition of these data, we conclude that most LGN cells are ap proximately space-time separable. An analysis of the timecourses of th e first singular values revealed a strongly bimodal but continuous dis tribution of rise times and waveforms. The two modes represented cells generally associated with the lagged and nonlagged classes of Mastron arde (1987a,b), and this was confirmed by their responses to step and sine-modulated spots in their field centers. The intermediate cells, r ather than appearing to constitute a separate group, smoothly filled t he region between the obviously lagged and nonlagged cells in every re spect. These conclusions are limited to X-cells although the data from a much smaller population of Y-cells conform to the same scheme. We c onclude that lagged and nonlagged cells represent the modes of a conti nuous and very broad distribution of temporal responses in the cat LGN .