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Matthew Patten, Andrew Welchman; Neural activity in higher dorsal visual areas relates to the discrimination of disparity-defined depth position. Journal of Vision 2010;10(7):366. doi: 10.1167/10.7.366.
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© ARVO (1962-2015); The Authors (2016-present)
Neural responses to binocular disparity have been observed throughout the visual cortex. Although it is thought that the ventral and dorsal pathways perform distinct roles in the perception of depth, the nature of this processing is still far from being understood. To investigate the relationship between cortical activity and the perception of depth, we used neuroimaging techniques to test regions for cortical activity that varied in a perceptually-relevant manner and compared this to the behavioural performance from a near-far depth discrimination task which was measured concurrently. Participants viewed random dot stereograms depicting planes with crossed (near) or uncrossed (far) disparity and were asked to judge the depth position (near or far). Performance was manipulated parametrically by changing the correlation of dots presented to the two eyes. When 100% of the dots were correlated (e.g. white dots in one eye match white dots in the other) the task was trivial; however, when 100% of the dots were anticorrelated (white dots in one eye match black dots in the other), discrimination performance was reduced to chance. We measured concurrent event-related fMRI responses and used multivariate analysis methods (SVM: support vector machine) to determine cortical regions that contained information about the disparity-defined depth (cf. Preston et al, 2008, J Neurosci, 28, 11315-27). In particular, we trained an SVM to discriminate near/far depth for 100% correlated stereograms and then tested the SVM with fMRI responses evoked at lower coherence levels, thereby obtaining ‘fMR-metric’ functions. Comparing fMR-metric and psychometric functions indicated a close association between psychophysical judgments of depth and activity in higher dorsal areas V7 and VIPS. Consistent with recent findings, our results demonstrate an important role for higher dorsal areas in the perception of disparity-defined depth.
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