Visual Physiology

Welcome to the visual physiology interactive tutorial.

Follow the route of visual processing from the eyes, through the Lateral Geniculate Nucleus, and up to the cortex. After you have explored the visual system, test your knowledge with the quiz.

[Historical Introduction]

[ The Eye | The Lateral Geniculate Nucleus | The Visual Cortex | Quiz ]

Historical Introduction (... or 'why do we need to know this?')

The anatomy of the connections between eye and brain has been known since the turn of the century. However, knowledge of circuit diagrams alone is not enough to infer neural function. Before recordings of activity in individual cells became available in the 1950's, theories of perception were inspired by anatomy. The brain was known to contain huge numbers of cells, massively interconnected (but only over short distances) in circuits that are similar over the whole cortex. Studies of localised brain damage (eg. following gunshot wounds) also showed that the visual cortex was mapped topographically. These facts inspired the Electrical Field Theory of perception.

Visual patterns were thought to set up corresponding fields of electrical activity across the surface of the cortex (see the picture above). Perceptual organisation in complex displays was said to be governed by interactions between these current fields. Experimental tests of the theory included attempts to short-circuit the electrical fields by pinning metallic strips across the surface of the cortex in rhesus monkeys, and then performing tests of visual functioning (eg. Lashley et al., Psych. Rev. 58, 123-136, 1951).

Of course we now know that, despite anatomical uniformity, functional properties vary hugely from cell to cell and from area to area in the cortex. The key word is specialisation rather than uniformity of function. The known functional properties of cells, and the architecture of the cortex, place fundamental constraints on the nature of perceptual theories.

So an understanding of cell properties is essential before progress can be made in developing and evaluating theories of perception.

Created by George Mather, University of Sussex (georgem@biols.susx.ac.uk) . Some of the images and text used in these pages were originally developed at the Department of Psychology, York University, as part of the GRASP project.