The central nervous system of humans supports a range of cognitive functions that contribute to conscious mental states. The neural systems underlying several of these cognitive functions, including perception, memory, planning and action, are proving susceptible to experimental analysis in lower primate species such as rhesus monkeys. In particular, recent investigations have generated striking new insights concerning the neural mechanisms that mediate visual perception. We briefly review the functional organization of the primate visual pathways and describe new experiments that demonstrate a causal link between neural activity in one of these pathways and a specific aspect of perceptual performance. The experiments illustrate an incisive method for linking perceptual abilities to their neural substrates. This approach may prove applicable to the analysis of other cognitive functions as well.