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

Brad C. Motter
The Journal of Neuroscience, September 20, 2006 • 26(38):9683–9694

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.