Abstract
Successful recognition of objects in cluttered scenes entails integration of fragmented images across space and time. Previous work focused on the integration of visual information across space. However, little is known about spatiotemporal integration that involves storing discrete image components in short-term memory and binding them across space and time. Our psychophysical work showed that collinear contours are reliably detected and identified when moving behind a narrow slit, suggesting that the spatiotemporal contour integration may not depend on V1 horizontal connections that are thought to underlie spatial contour integration. In the current study we used fMRI to investigate the neural mechanisms that mediate spatiotemporal contour integration under slit-viewing. The stimuli comprised arrays of randomly orientated Gabor patches, either with (contour stimuli) or without (random stimuli) embedded contour paths. The contour stimuli contained five embedded contours each comprising 4~9 collinear Gabor elements. The global orientation of the contours was jittered between 30°-45° or 135°-150°. In a blocked design the contour or random stimuli moved behind a slit whose width (0.75°) was equal to the average inter-element distance. As a result, at any given moment only one or parts of two contour elements could be seen through the slit. Within a block of trials a small proportion (12.5%) of stimuli contained vertical contours as targets. Observers were instructed to detect the target stimuli. A GLM analysis showed stronger fMRI responses to contour stimuli than random stimuli in higher dorsal visual areas (V7, V3B/KO, VIPS) and in the LOC, suggesting that spatiotemporal integration involves interactions between ventral and dorsal visual areas. We hypothesize that the dorsal areas may contribute to binding moving contour elements across space and time, and that the ventral regions may generate the integrated percept of the global contour.
This work was supported by grants from the Biotechnology and Biological Sciences Research Council to ZK [D52199X, E027436].