Visual Prosthesis
A. Introduction

A variety of invasive procedures have also been developed. So far, however, only with limited success. The most frequently used method is electrical stimulation of neural tissue. The idea here is to convert visual signals collected by a camera or other sensing device into electrical impulses that are applied to brain tissue. It has been shown that electrical stimulation can elicit visual percepts in several brain areas. The visual impression created by stimulation of a single site has often been referred to as a "phosphene". The areas that have been electrically stimulated include the retina, the lateral geniculate nucleus of the thalamus, primary visual cortex and higher visual areas. Among these we believe that primary visual cortex holds the greatest promise for developing a visual prosthesis. This area has a well-defined topographic layout. An array of electrodes can be implanted to selectively stimulate different representations of the visual field. However, there are numerous problems that must be solved before such a device can become effective.