Vision Group Research

Neural basis of visual perception

Over one third of our brain is dedicated to processing visual information, which is not surprising as we must somehow get from patterns of light detected by the photoreceptors to a three-dimensional world that is full of colour.
 

1. Processing stereoscopic depth information in the human cortex

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.
 

Collaborators: Andrew Parker, John Elston.

2. Investigating the effects of peripheral visual impairment on the brain

Anophthalmia is a condition in which the eyes fail to develop and, if both eyes are affected, leads to a total lack of vision.  We are interested in how the areas of the brain that would normally be involved in processing visual information are affected by anophthalmia.  We are using diffusion imaging to look at whether connections within the brain are different in these patients.  Using fMRI we can look at whether brain areas usually used for visual perception are used instead for processing of other information.

In collaboration with Dr Ione Fine at the University of Washington we are comparing the brains of subjects with anophthalmia with those who lost vision early in life.
 

Collaborators: Nicola Ragge, Alan Cowey, Iona Alexander, Kate Watkins, Ione Fine.

3. Very high resolution imaging of the visual cortex

Recent advances in MR technology have allowed the imaging of myeloarchetecture in the human cortex. We can scan the occipital lobe at an in-plane resolution of 0.3mm x 0.3mm to reveal patterns of myelin within the cortex. The primary visual cortex, or area 17 is often known as the striate cortex due to a thick bundle of myelinated fibres that run through layer 4 (stria of Gennari). Using our retinotopically defined V1, we can measure the correspondence of the anatomically and functionally defined V1 in individual subjects.

Distinct myleoarchitecture patterns exist throughout the cortex, and further development of these techniques may allow the identification of such areas in vivo. The installation of a 7 Tesla scanner at the FMRIB Centre will facilitate this research.

fMRI data at very high resolution will be used to uncover the functional architecture of the early visual areas.

Collaborators: Stuart Clare, Denis Schluppeck, Susan Francis.
 

4. Investigating the effects of hemianopia on the visual pathway

Following damage to the visual pathway, patients can be left unable to see in the visual field contralateral to the damage. Damage can occur at different stages of the visual pathway, including the optic tract, the lateral geniculate nucleus or the visual cortex. The patients will have different residual visual abilities depending on where the damage occurs. We are currently investigating the effects of damage at different stages of the visual pathway and the changes that occur over time following damage. 

Collaborators: Chris Kennard, Gordon Plant, John Barbur, Panitha Jindahra