ABSTRACT
Picture a table set for a holiday banquet with multiple place settings-each with knives, forks, spoons, plates, and glasses-as well as candelabras, serving bowls, condiments, chairs, and the table itself. The visual information that will ultimately yield an internal representation in which object identities are registered and their locations computed in a fashion that affords action, is registered by retinal cells that contain a variety of light-sensitive molecules that influence the firing rates of the cells. From this seemingly impoverished input that yields only a representation of light and, in a restricted spatial domain, color, the rich depiction of the visual world is generated by means of a series of transformations and elaborations. Although under normal circumstances visual processing is effortless and remarkably efficient, the construction of an internal representation of the visually perceived world around us is, in fact, complex, as witnessed by the fact that it may be disrupted in strikingly different manners by brain dysfunction. This chapter focuses on one aspect of visual processing-the manner in which visually presented objects are identified and how this process breaks down, culminating in the disorder of visual object agnosia. We start with a brief historical overview of the disorder. In an effort to frame the subsequent discussion, a brief description of the processes underlying visual processing will be presented. Classical disorders of visual object recognition as well as several recently described disorders will be discussed with reference to this theoretical framework.
