Heterogeneity of extrastriate visual areas and multiple parietal areas in the macaque monkey.

The definition of visual areas remains a key problem in the effort to elucidate cortical functions. Visual areas vary along a number of dimensions and are increasingly difficult to define according to traditional criteria at higher levels of the hierarchy. Three recently discovered areas in monkey parietal association cortex illustrate a new approach to this problem. Their definition depends on assessment of neuronal response properties in the alert, behaving animal combined with precise reconstruction of recording sites. This approach permits recognition of functionally distinct areas in the absence of retinotopic maps.