He was a research scientist in the Artificial Intelligence Laboratory at MIT and the Division of Applied Sciences at Harvard University from 1982 to 1988. He served as an assistant and associate professor at Harvard until 1996. He was a senior research scientist at the Smith-Kettlewell Eye Research Institute from 1996 to 2002. He joined the University of California, Los Angeles, as a full professor with a joint appointment in statistics and psychology in 2002. He obtained a joint appointment in computer science in 2007. His research interests include computational models of vision, mathematical models of cognition, and artificial intelligence and neural networks.