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Abstract:
A wide range of salient visual stimuli can be made to suddenly disappear from view following the onset of a large surrounding pattern (generalized flash suppression, GFS, Wilke et al (2003)). The interaction of two factors has previously been found to maximize the probability of perceptual suppression in the context of GFS: some kind of interocular interaction other than spatial conflict, combined with the introduction of approximately a second temporal delay between target and surround onset (stimulus onset asynchrony, SOA). In the present study we examined the neurophysiological basis of this observation by means of multielectrode recordings in area V4 of awake monkeys. Specifically, we were interested in whether the increased probability of perceptual target suppression with longer SOAs could be explained by a decay in the firing rate of neuronal populations responding to the target. To test this, we systematically varied the time between target and surround onset between 0 ms (simultaneous onset) and 1400 ms under different ocular configurations. By subtracting neuronal activity in ‘target only’ trials from ‘target + surround’ trials for a given SOA, we found significant neuronal suppression only with the SOA times that reliably led to perceptual disappearance. Further matching perception, maximal attenuation occurred at a mean latency of about 130 ms to 200 ms after surround onset - approximating the previously measured latency to subjective disappearance in GFS. Moreover, optimal suppression was achieved with incongruent ocular target/surround configurations. These data suggest that response modulations in area V4 are closely related to perception during GFS, and that neural adaptation cannot alone account for the all-or none perceptual disappearance of the target.
