TEMPORAL-FREQUENCY SELECTIVITY IN MONKEY VISUAL-CORTEX

We investigated the dynamics of neurons in the striate cortex (V1) and the lateral geniculate nucleus (LGN) to study the transformation in t emporal-frequency tuning between the LGN and V1. Furthermore, we compa red the temporal-frequency tuning of simple with that of complex cells and direction-selective cells with nondirection-selective cells, in o rder to determine whether there are significant differences in tempora l-frequency tuning among distinct functional classes of cells within V 1. In addition, we compared the cells in the primary input layers of V 1 (4a, 4c alpha, and 4c beta) with cells in the layers that are predom inantly second and higher order (2, 3, 4b, 5, and 6). We measured temp oral-frequency responses to drifting sinusoidal gratings. For LGN neur ons and simple cells, we used the amplitude and phase of the fundament al response. For complex cells, the elevation of impulse rate (FO) to a drifting grating was the response measure. There is significant low- pass filtering between the LGN and the input layers of V1 accompanied by a small, 3-ms increase in visual delay. There is further low-pass f iltering between V1 input layers and the second- and higher-order neur ons in V1. This results in an average decrease in high cutoff temporal -frequency between the LGN and V1 output layers of about 20 Hz and an increase in average visual latency of about 12-14 ms. One of the most salient results is the increased diversity of the dynamic properties s een in V1 when compared to the cells of the lateral geniculate, possib ly reflecting specialization of function among cells in V1. Simple and complex cells had distributions of temporal-frequency tuning properti es that were similar to each other. Direction-selective and nondirecti on-selective cells had similar preferred and high cutoff temporal freq uencies, but direction-selective cells were almost exclusively band-pa ss while nondirection-selective cells distributed equally between band -pass and low-pass categories. Integration time, a measure of visual d elay, was about 10 ms longer for V1 than LGN. In V1 there was a relati vely broad distribution of integration times from 40-80 ms for simple cells and 60-100 ms for complex cells while in the LGN the distributio n was narrower.