Visuotopic Organization of Primate Extrastriate Cortex

Abstract

One of the fundamental aspects of the organization of extrastriate visual cortex in mammals is the presence of multiple representations of the visual field. Although the existence of these visuotopic maps has been known for more than 50 years (Talbot, 1942), there are still many open issues regarding their organization. Descriptions of the number, boundaries, and visuotopic organization of cortical visual areas vary not only among primates, but also between studies of single species by different groups (e.g., Fig. 1; see Table I for abbreviations). It is not clear whether these differences reflect real individual or interspecies variability, or whether they merely reflect the need for more study or better criteria for the definition of visual areas. The aim of this chapter is to review the current evidence related to the precision, extent, and topological characteristics of visuotopic maps in extrastriate areas of primates. A critical evaluation of the published evidence on these subjects reveals that some of the present points of contention are the result not only of the complexity of the problem, but also of the scarcity of the data available for interpretation. Response properties, architecture, connections, and nodular patterns can also be used to lend or deny support to specific hypotheses generated on the basis of visuotopy, but these criteria will not be reviewed in detail here.