Backus, B., Fleet, D.J., Parker, A.J. and Heeger, D.J.
Human cortical activity correlates with stereoscopic depth perception.
Journal of Neurophysiology 86(10):2054-2068, 2001.
Stereoscopic depth perception is based on binocular
disparities. Although neurons in primary visual cortex (V1) are
selective for binocular disparity, their responses do not explicitly
code perceived depth (Cumming and Parker 2000). The stereoscopic
pathway must therefore include additional processing beyond V1. We
used functional magnetic imaging (fMRI) to examine stereo processing
in V1 and other areas of visual cortex. We created stereoscopic
stimuli that portrayed two planes of dots in depth, placed
symmetrically about the plane of fixation, or else asymmetrically with
both planes either nearer or farther than fixation. The interplane
disparity was varied parametrically to determine the stereoacuity
threshold (the smallest detectable disparity) and the upper depth
limit (largest detectable disparity). fMRI was then used to quantify
cortical activity across the entire range of detectable interplane
disparities. Measured cortical activity covaried with psychophysical
measures of stereoscopic depth perception. Activity increased as the
interplane disparity increased above the stereoacuity threshold, and
dropped as interplane disparity approached the upper depth limit. The
V1 measurements were consistent with a post-hoc analysis of
electrophysiological recordings of single neurons in
macaques. Although there was widespread activity within the
extrastriate cortex (consistent with electrophysiological recordings
of single neurons), area V3A showed remarkable sensitivity to
stereoscopic stimuli, suggesting that neurons in V3A may play a
special role in the stereo pathway.
Return to David Fleet's home page.