The processing of three-dimensional shape from disparity in the human brain

Area of Science:

• Neuroscience
• Visual Perception
• Computational Neuroscience

Background:

• Three-dimensional (3D) shape perception is crucial for object recognition and visuomotor control.
• While 3D shape from motion is understood, extraction from disparity (stereo vision) remains less clear.
• Previous monkey fMRI studies identified neural signatures for second-order disparity processing.

Purpose of the Study:

• To investigate the human brain regions involved in extracting 3D shape from stereo disparity.
• To identify the neural correlates of processing second-order disparity cues in humans.
• To compare human and monkey brain regions involved in 3D shape from stereo vision.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used in human subjects.
• Stimuli manipulated stereo presence and disparity order (zero vs. second order).
• Control experiments excluded attention and eye movements as confounds.

Main Results:

• Five intraparietal sulcus (IPS) regions, V3, V3A complex, posterior inferior temporal gyrus (ITG), and ventral premotor cortex (vPrCS) were identified.
• Specific IPS regions (DIPSM, DIPSA, phAIP), posterior ITG, and vPrCS align with monkey homologues.
• Occipital (V3A) and occipitoparietal (VIPS/V7*, POIPS) regions appear evolutionarily novel or modified.
• Activity in occipital regions correlated with perceived depth amplitude.

Conclusions:

• The human brain utilizes a distributed network, including novel occipital and occipitoparietal areas, for 3D shape extraction from stereo disparity.
• This study provides a detailed map of human stereo-defined 3D shape processing.
• Findings offer insights into the evolution of visual processing pathways for depth perception.