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Sarah Kromrey, Shalon Howard, Jay Hegdé; Neural Mechanisms of Perception of Depth-Order from Motion: A Human fMRI Study. Journal of Vision 2010;10(7):49. doi: 10.1167/10.7.49.
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© ARVO (1962-2015); The Authors (2016-present)
When one visual object moves behind another, it provides a compelling sense of which object is closer to the viewer and which object is farther in depth. This percept is referred to as depth-order from motion (DFM). The neural mechanisms of DFM are largely unclear, including the relative roles of the first-order (i.e., luminance-based) vs. the second-order (i.e.,non-luminance-based) motion processing mechanisms, and the relative contributions of the two know types of DFM cues, the accretion-deletion (AD) cue and the common motion (CM) cue. We performed a whole-brain fMRI scan using a mixed (i.e., events-within-blocks) design, which allowed us to compare the responses across blocks as well as across individual trials. Depending on the stimulus block, subjects were shown either stimuli that elicited depth-order percepts, or stimuli that did not. Stimuli that elicited the depth-order percept contained both types of motion and both types of DFM cues. During each trial of each stimulus block, subjects reported the perceived depth-order using a button press. We found significantly greater responses to depth-order stimuli relative to non-depth-order stimuli in several early retinotopic regions, including V1, V2, V3, V3A, and V4v. The response in V3A reliably reflected, on a trial-to-trial basis, whether the subjects perceived depth-order (logistic regression; group data, N = 5; p <0.05). However, we were unable to find any region that was differentially responsive to near vs. far depth-order stimuli, or to the corresponding percepts. Importantly, neither V5/MT+ nor the kinetic occipital region (KO) showed significant differential responsiveness to the DFM stimuli across subjects (p > 0.05), although the responses in both regions showed a slight response suppression by the depth-order stimuli in some subjects. Together, these results identify specific brain regions may play an important role in DFM cue processing and mediate DFM perception.
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