Cortical Off Response Tuning for Stimulus Duration

To answer the question whether OFF response amplitude (firing rate) of visual cortical cells varies as a function of stimulus duration, a series of such cells from areas 17 and 18 of the cat were investigated with a stationary light bar, presented for different durations (10-3200 msec) over the receptive field. Out of a sample of 174 cells tested, 58 cells were found for which the OFF responses varied as a function of ON stimulus duration. Of these cells, 29 showed a continuous increase up to the longest duration tested, six showed a sharp tuning for medium range durations (between 50 and 400 msec) and the remaining 23 cells had an intermediate profile (increase to optimum followed by slight decrease). For some of these cells this tuning could be used to predict adequately the velocity tuning. Similar recordings in 13 lateral geniculate nucleus cells failed to show duration tuning.