Visual acuity is a measure of the keenness of sight. The Egyptians used the ability to distinguish double stars as a measure of visual acuity more than 5000 years ago. Over the centuries visual acuity has been studied, measured and…
Introduction Vision is our most developed sense and unsurprisingly a substantial amount of brain processing is devoted to it, with over half the primate brain involved in vision-related processing. A first step in understanding the nature of this processing involves…
What is extrastriate visual cortex? The term “extrastriate” refers to all visually responsive cortex other than primary visual (striate) cortex, and does not receive strong direct projections from the lateral geniculate nucleus (LGN) (see Chapter 30 ). A central hypothesis…
Overview: The primary visual cortex constructs local image features The visual system provides a description of the location and identification of objects that have survival value to the species. This description must be made in a dynamic world in which…
The lateral geniculate nucleus: the gateway to conscious visual perception Conscious perception requires the visual information that passes through the dorsal lateral geniculate nucleus (LGN) in primates. Although the retina sends axons to many subcortical nuclei, only the pathway from…
Introduction The two optic nerves carry the axons of retinal ganglion cells (RGCs), and along these axons transmit all of the visual information from the inner retina ( Chapter 23 ) to the brain ( Chapter 29, Chapter 30, Chapter…
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Overview In the past decade, compelling evidence has emerged for a novel class of photoreceptors in the mammalian retina. These neurons are ganglion cells that express the photopigment melanopsin and respond autonomously to bright light with a sustained depolarization and…
The pupillary opening appears to occupy a central location, but if carefully measured, it is actually situated slightly inferior and nasal to the center of the cornea. Thus, the pupil center may not correspond exactly to the optical axis defined…
Introduction The electroretinogram (ERG) is a useful tool for objective, non-invasive assessment of retinal function both in the clinic and the laboratory. It is a mass electrical potential that represents the summed response of all the cells in the retina…