Behavioural ecology and retinal cell topography

Abstract

The vertebrate retina is an extension of the brain, a hemisphere of neural tissue upon which is mapped an image of a particular species visual environment. Each point in visual space is subtended by a corresponding point on the neural retina which in turn is retinotopically mapped onto the visual centres of the brain. Light energy or the ‘optical image’ is transformed into electrical energy or a ‘neural image’ by the photoreceptors and, via a number of interneurons (bipolar, amacrine and horizontal cells), these signals reach the ganglion cells each of which possess an axon carrying information to the central nervous system via the optic nerve. Although processing at the level of the photoreceptors may not necessarily change the neural image, due to the over abundance of photoreceptors relative to the number of ganglion cells, it is the ganglion cells which ultimately define the perception of a species’ environment received by the central nervous system.