Topographical representation of binocular depth in the human visual cortex using fMRI.
Bridge H., Parker AJ.
We used binocular stimuli to define how the visual location of stereoscopic depth structure maps topographically onto the human visual cortex. The main stimulus consisted of a circular disk of dots, most at zero-disparity, against which a single quadrant was defined with changing disparity ('correlated' disparity), and moved around the visual field. The second stimulus had exactly the same structure, except that the disparity in the quadrant was 'anticorrelated,' that is black dots in one eye were paired with white dots in the other. Unlike the correlated stimulus, this 'anticorrelated' stimulus did not lead to a perception of depth. The activation maps to these disparity stimuli are very similar to those produced using stimuli defined by luminance or motion. The lateral area of the occipital lobe showed the largest difference in response to correlated, as opposed to anticorrelated, disparity. This region included human MT/V5 and two areas, LO-1 and LO-2, recently defined as retinotopically distinct areas within area KO. All these areas, plus V3 and hV4, showed a significantly larger response to the correlated stimulus, compared to the anticorrelated stimulus. No other visual areas showed a significant difference in response. However, the responses to correlated disparity were significantly more reliable than those to anticorrelated in all areas, except V1. Although there are considerable differences in the experimental approach, our fMRI results are broadly consistent with primate neurophysiology showing responses to anticorrelated disparity in V1 neurons.