Local and global systems revealed in image segmentation during bistable percepts of three ambiguous figures: “Schroeder's Staircase”, the “Rubin Face-Vase figure”, and the “Ebbecke Ring”

Abstract

How the perceptual system segregates, sorts, and binds features of objects to form unified percepts from a complex visual world is a central question in vision research. Since the bistable percepts of ambiguous stimuli are purely subjective, they can be used to isolate mechanisms of perceptual binding from stimulus-dependent modulations. High resolution functional magnetic images, fMRI, (1.5×1.5×13mm) were acquired while subjects maintained one of the two-bistable percepts of “Stroder's Staircase”, the “Rubin Face-Vase” figure, and the “Ebbecke Ring”. A random-effects group analysis (SPM2) revealed a widely distributed global circuit including frontal, parietal, and occipital regions that was activated for all figures. Fusiform face area was significantly more active during the perception of the face versus the vase percept for the Face-Vase figure. Furthermore, distinct regions of the right inferior parietal lobule were more active while viewing one percept of a figure over the other. These results were consistent across all 3 ambiguous figures suggesting a generalized mechanism for image segmentation, and lead to two important conclusions: (1) high-level mechanisms are involved with the maintenance of a percept of bistable figures (2) activity in distinct local populations of neurons in the inferior parietal lobule are involved in perceptual grouping and binding of visual input.