The neural basis of binocular depth perception

Patten, Matthew Lindsay (2013). The neural basis of binocular depth perception. University of Birmingham. Ph.D.

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Abstract

How does the human visual system convert two-dimensional projections from our eyes into a three-dimensional percept? One primary method is from binocular disparities, which result from having two horizontally separated eyes and are used to provide a powerful cue to depth in our environment. In this thesis, I use human fMRI to investigate the cortical signals associated with binocular disparity. I address several core issues, including the relationship between cortical activity and perception, the significance of the reference plane on depth configurations, and the topography of disparity signals on the cortical surface.

In measuring responses to coarse and fine disparities, researchers typically engage two respective tasks: a signal-in-noise and a feature difference task. In the first chapter, we decouple the disparity magnitude from the perceptual task and examine cortical responses to both of these tasks when using fine disparities. Further, we manipulated performance and identified visual areas whose activity varied in line with perceptual judgments. We reveal that responses in later dorsal regions VIPS and POIPS were closely related to perception for both tasks. In the second chapter, we used a similar manipulation to investigate cortical regions that have solved the correspondence problem and whose responses were consistent with the depth percept of the observer, and reveal that this takes place in V7 and VIPS.

The third chapter examines the importance of the reference in disparity calculations. We performed several classifications based on depths that were considered relative to fixation or relative to the surround. We found that early visual areas were most sensitive to disparity edges; dorsal visual areas used both the fixation plane and the surround in computing disparity whereas ventral visual areas processed disparity with reference to the surround.

In the fourth chapter, we attempt to identify a topographic organisation of binocular disparity in the visual cortex. We estimate the disparity preferences of each voxel in two distinct ways, and displayed these preferences on a flatmap of the cortical surface. Although we did not observe a topographic map of disparity, we observed a cluster in intermediate dorsal regions (V3A, V3B/KO, V7) that consistently showed a bias towards crossed disparities of a larger magnitude.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):