Seeing in 3D
Understanding the neurochemistry of binocular vision using MR Spectroscopy
A major problem that our visual system faces is how to extract three-dimensional information from our two-dimensional retinae. One of the ways in which this is achieved is known as binocular stereopsis. Differences in the two retinal images are used to calculate the position of objects in space. The primary visual cortex is the first area in the visual system that contains neurons receiving input from both eyes. Some of these neurons are sensitive to "binocular disparity", that is they modulate their firing rate according to whether stimuli lie in the same, or different places on the two retinae. However, simply showing sensitivity to disparity does not necessarily mean that these neurons are involved in the perception of depth. A series of papers by Cumming & Parker showed that in fact the response of these disparity selective neurons in V1 do not correspond well with perceived depth. However, in higher visual areas, such as inferotemporal cortex, the neuronal responses appear to correspond to perception.
We have a stereoscopic projector that allows us to present images separately to the two eyes in the scanner and are currently investigating the roles of dorsal and ventral visual cortex in depth perception. This work with shortly be extended to investigate the visual systems of subject who have suffered binocular dysfunction as children.
These projects led by Dr Betina Ip, a Royal Society Dorothy Hodgkin Fellow, in collaboration with Professor Andrew Parker.