The living anthropoids tend to have large brains, small olfactory bulbs, and high acuity vision compared with other primates (Baron et al., 1983; Stephan et al., 1981). An interesting possibility is that an increasing emphasis on vision was in some way related to increases in brain size in the anthropoid lineage. It is certainly plausible that changes in sensory behavior would necessitate major changes in the brain. Comparative neuroanatomical data has suggested that brain size increases were related to growth in the parvocellular layers of the lateral geniculate nucleus, an early stage in the visual processing hierarchy (Barton, 1998).