Abstract
Electrophysiological evidence suggested primarily the involvement of the middle temporal (MT) area in depth cue integration in macaques, as opposed to human imaging data pinpointing area V3B/kinetic occipital area (V3B/KO). To clarify this conundrum, we decoded monkey functional MRI (fMRI) responses evoked by stimuli signaling near or far depths defined by binocular disparity, relative motion, and their combination, and we compared results with those from an identical experiment previously performed in humans. Responses in macaque area MT are more discriminable when two cues concurrently signal depth, and information provided by one cue is diagnostic of depth indicated by the other. This suggests that monkey area MT computes fusion of disparity and motion depth signals, exactly as shown for human area V3B/KO. Hence, these data reconcile previously reported discrepancies between depth processing in human and monkey by showing the involvement of the dorsal stream in depth cue integration using the same technique, despite the engagement of different regions.
Highlights
Visual environments provide a range of cues that allow the brain to extract depth structure from the ambiguous images projected onto the two-dimensional (2D) retinas
We used functional MRI (fMRI) monocrystalline iron oxide nanoparticle (MION) responses measured while subjects were presented with stimuli depicting near versus far depths defined on the basis of binocular disparity, relative motion, and their combination
We quantified the discriminability of fMRI responses by training a support vector machine (SVM) to classify patterns of activity evoked by stimuli depicting near versus far depth configurations
Summary
Visual environments provide a range of cues that allow the brain to extract depth structure from the ambiguous images projected onto the two-dimensional (2D) retinas. A fundamental challenge in visual neuroscience is to understand how this 2D information is processed and integrated, to allow the viewer to perceive and act in a three-dimensional (3D) world. While multiple regions of the macaque [1] and human [2] brain have been found to respond to images that depict depth, it is only recently that we have begun to understand how information from different signals is fused together. While many studies demonstrated that regions of cortex could respond to information conveyed by two different cues (such as depth from binocular disparity, and depth from motion), this alone does not imply that information is fused into a common representation. Differentiating responses to fused versus independent signals requires careful assessment of neural responses to presentations of stimuli in which information from the two different cues is manipulated independently
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