Abstract
Motion induced blindness (MIB) is a visual phenomenon in which a salient static target spontaneously fluctuates in and out of visual awareness when surrounded by a moving pattern. We characterized the modulation of neural activity in multiple human visual areas correlated with perceptual re-organization during MIB. Observers reported the subjective disappearance and re-appearance of a high-contrast target contour surrounded by a moving random dot pattern (the mask) while neural activity was measured with fMRI. We identified the sub-regions of each visual area in each observer that corresponded to the target and the mask. For each of these sub-regions, average fMRI response time courses were estimated during the disappearance and re-appearance of the target. Responses in target-specific sub-regions of V1 through V4 decreased with target disappearance and increased with re-appearance. These responses were particularly strong in V4 and were followed by a delayed global modulation expressed throughout V1-V4. Mask-specific sub-regions in dorsal stream areas MT and the posterior intraparietal sulcus (IPS) exhibited the opposite pattern of modulation; responses increased with target disappearance and decreased with target re-appearance. The responses time courses in the mask-specific sub-regions of MT and IPS were anti-correlated with the response time courses in the target-specific sub-regions of V2, V3, and V4. Our results demonstrate that the spontaneous perceptual re-organization during MIB has multiple distinct neural signatures in human visual cortex. The responses of the target sub-regions of early ventral stream areas specifically reflect observers' fluctuating awareness of the target.
Supported by grants from the Leopoldina National Academy of Science (BMBF-LPD 9901/8-136, T.D.) and the NIH (R01-EY16752, D.H.).