Neural systems and circuits for visual perception
- Understanding the processing of binocular stereoscopic depth and 3-D shape by neurons in the visual cortex
- Systematic comparisons between single neurons and perception
- Neural communication between cortical areas
The responses of neurons in the primary visual cortex (V1) to binocular depth differ in characteristic ways from how depth is actually perceived. A crucial, novel step was to show that anti-correlated random-dot stereograms (patterns of opposite contrast in the two eyes) produce ‘tuned’ responses from neurons in the primary visual cortex. The same patterns do not support normal stereoscopic depth perception. We have also determined at the physiological level a significant distinction between absolute and relative disparity detection, with the important discovery that neurons in the primary visual cortex respond only to absolute disparity, whilst some neurons in the extrastriate cortex are specialized for encoding relative disparity. We are also interested in what stereoscopic depth perception can tell us about spatial cognition in general.
Therefore, the primary visual cortex is crucial for processing stereoscopic information, but it is only a preliminary stage in the generation of a full stereoscopic depth percept. This insight alters our view of clinical conditions, such as amblyopia, in which there is a loss of binocular function. Up to now, the focus has been on the loss of binocularity in V1: our work makes clear that loss or dysfunction of neurons outside V1 may be crucial. To search for those sites in the visual cortex, we are continuing our neurophysiological studies and have initiated the use of functional magnetic resonance imaging (fMRI) at high field strength (7-Tesla) to examine the role of human extrastriate cortex in stereoscopic depth perception