Neural correlates of induced perceptual disappearance

Which conditions are necessary and sufficient for the brain's generation of a visible percept under natural viewing conditions?

We might take as a necessary requirement the presence of a physical pattern of light striking the retina. The activation of retinal neurons will cause a cascade of activity coursing its way through the visual system which can then be registered by the brain, and ultimately contribute to perception. But is this sort of automatic sensory response a sufficient condition for a stimulus to be perceived? This question is underscored by the variety of visual suppression phenomena, in which normally visible targets are rendered completely invisible. We developed a paradigm that permits a host of salient and attended patterns to suddenly disappear from view, and remain invisible for up to several seconds and investigated it with psychophysical methods in humans and monkeys (Wilke et al., 2003).

In addition, multielectrode recordings were performed in the visual cortex (V1, V2 and V4) of awake and reporting/fixating monkeys under visual stimulation leading to perceptual suppression. We found that whereas the early visual cortex plays an important role in the detection of congruent vs. incongruent visual stimulation, the changes in neuronal firing rate according to stimulus visibility are rather subtle in comparison with a physical stimulus removal.