text: Significance The visual system of primates contains a large number of separate representations of the visual world, at least 20 at latest count. One of the central problems of visual science is to establish how the numerous areas together form our seemingly unified visual experience. Objectives The multiple areas clearly are connected in a complex network that contains both serial and parallel organization. I have projects exploring both aspects of the organization, employing single-neuron physiological methods to measure information processing in the cortex of rhesus macaques (Macaca mulatta). We employ a combination of physiological and behavioral approaches to explore the relationship of signals in different cortical areas to different aspects of visual perception. Results Cortex, MT and MST. These form a perfect example of serial processing, and we already know a great deal about how they are organized and what kind of information they represent. Both appear to be specialized for the analysis of visual motion, but MST (the later stage of processing) appears to represent much more complex aspects of image motion, such as rotation, expansion, and contraction. We have established that area MST is involved in one complex motion task, recovering the direction of self motion from optic flow (analogous to the "Star Wars" opening graphic), using the method of introcortical microstimulation to minutely perturb the signals carried by neurons there. We have also explored parallel organization by measuring color responses in area MT, long thought to be specialized for motion analysis and not color. We have discovered robust color signals in MT and are carefully characterizing their nature. Future Directions We will continue to explore the mechanisms of perception of self-motion, and will also initiate a similar study on a related complex motion task, in which individual motion cues can be better isolated and controlled. KEY WORDS visual perception, motion processing, neurophysiology, modeling FUNDING NIH Grant EY10562 PUBLICATIONS Britten, K.H. Clustering of response selectivity in the medial superior temporal area of extrastriate cortex in the macaque monkey. Visual Neuroscience 15(3):553-558, 1998. Britten, K.H. and van Wezel, R.J.A. Electrical microstimulation of cortical area MST biases heading perception in monkeys. Nature Neuroscience 1(1):59-63, 1998. Britten, K.H. and Newsome, W.T. Tuning bandwidths for near-threshold stimuli in area MT. Journal of Neurophysiology 80(2):762-770, 1998.