Cue-invariant 3-D shape representation in monkey cortex using fMRI

Previous work using fMRI in anesthetized monkeys investigating the representation of 3-D objects defined by moving random dots or static texture cues revealed the presence of a network of areas responsive to 3-D shape in occipital, temporal, parietal, and frontal cortex (Sereno et al., Neuron, 2002). The goal of the present study was to determine the amount of activation overlap for 3-D surface shape defined with 3 different cues by directly comparing activation for the same 3-D shapes in the same scanning session. Stimuli consisted of a set of 3-D surfaces defined by dynamic (random dots with motion parallax) and static (shading and contour) shape cues. Each shape defined by a particular cue was paired with a control stimulus consisting of a scrambled or disrupted cue gradient. The control stimuli contain the same local information as the original surfaces (motion--dot speed and direction; shading--luminance range and pattern; surface contour--line shape and size). However, the disruption of the cue gradient across the image diminishes or abolishes an impression of depth. Activation from a comparison of intact to control stimuli revealed regions of common activation (e.g., in superior temporal, intra-parietal, and arcuate sulci) for shape defined by the 3 different cues. Our results suggest a set of candidate areas in monkey cortex for cue-invariant 3-D shape processing