Neural activity during induced visual suppression in the monkey

Following the onset of a large surrounding pattern, a wide range of salient visual targets can be induced to suddenly disappear. This phenomenon, resembling binocular rivalry flash suppression in its time course, and motion-induced blindness in its spatial arrangement, can be elicited in the absence of any interocular or local stimulus conflict (Wilke et al., 2002). In the present experiments, we investigate the neurophysiological basis of this phenomenon by performing multielectrode recordings from early visual areas of two trained adult monkeys. Using transdural multielectrode recording techniques, we monitored activity simultaneously in areas V1, V2, and V4 while monkeys kept fixation. Based on the parameters derived from both human and monkey psychophysical experiments, we first adjusted the stimuli to compare neural responses under two different stimulus conditions, one in which the stimulus disappeared, and another in which it remained continuously visible. Then, exploiting the subjective reports provided by the monkey, we next used an ambiguous set of parameters, and compared trials in which the stimulus disappeared to those in which it did not. We found that in area V1 only a small minority of neurons showed activity changes corresponding to the subjective disappearance of the stimulus, while in area V4, this fraction of neurons was significantly higher. We additionally found that the expression of perceptual suppression was often intricately linked with a reduction in responses to the flashed surround pattern, which generally elicited excitatory responses even when its closest elements were several degrees from the classical receptive field. It thus appears that the neural modulation associated with target visibility entails a complex interplay, either within or between visual areas, involving local receptive field activation and responses to global surround elements