Processing shape, motion, and three-dimensional shape-from-motion in the human cortex

TL;DR: High-resolution analysis showed that SFM objects and line drawings were processed in separate but adjacent sub-regions in SLO, suggesting that SLO codes object shape but retains topographic segregation based on shape cues.

Abstract: Shape and motion are complementary visual features and each appears to be processed in unique cortical areas. However, object motion is a powerful cue for the perception of three-dimensional (3-D) shape, implying that the two types of information — motion and form — are well integrated. We conducted a series of fMRI experiments aimed at identifying the brain regions involved in inferring 3-D shape from motion cues. For each subject, we identified regions in occipital–temporal cortex that were activated when perceiving: (i) motion in unstructured random-dot patterns, (ii) 2-D and 3-D line drawing shapes, and (iii) 3-D shapes defined by motion cues (shape-from-motion, SFM). We found closely adjacent areas in the lateral occipital region activated by random motion and line-drawing shapes. In addition, we found that the SFM stimuli produced a greater MRI signal in only one of the areas identified with the random motion and line-drawing stimuli: the superior lateral occipital (SLO) region. High-resolution analysis showed that SFM objects and line drawings were processed in separate but adjacent sub-regions in SLO, suggesting that SLO codes object shape but retains topographic segregation based on shape cues. Expanding the analysis to the entire cortex identified ap arietal area that had overlapping activation for both SFM and line drawings and increased MRI signal for 3-D versus 2-D shapes, suggesting this area is important for processing shape information.