Modulation of Transient and Sustained Response Components of V4 Neurons by Temporal Crowding in Flashed Stimulus Sequences

The responses of extrastriate area V4 neurons to flashed visual stimuli were examined to determine whether the responses to stimulus sequences occurring at normal saccade and fixation timing intervals were degraded relative to longer timing intervals. Stimuli were flashed in receptive fields in the near periphery while monkeys maintained steady fixation. Short interstimulus intervals (ISIs) resulted in an overall habituation style response reduction. The transient component of responses to preferred stimuli was suppressed, often completely, when the ISI was reduced below 100 ms into the range of saccadic durations. The sustained response component weakened but remained intact. At short ISIs the trailing activity from the preceding stimulus blended with onset activity from the next stimulus, making it difficult to detect individual stimulus onset events within the spike train. Habituation or conditioning effects were correlated with the stimulus tuning sensitivity of the neuron but only loosely associated with the actual level of V4 activation elicited by preceding stimuli. The results suggest that sharply tuned neurons, because of their probabilistic inactivity, are particularly sensitive to temporal change, whereas the sustained components of broadly tuned neurons could provide a continuity of information flow across visual transients, such as saccades, that do not alter significantly the view by the neuron of the scene.