Edward Chace Tolman was a prominent researcher and theoretician in the first half of the twentieth century. Operating within the behavioristic framework that dominated American experimental psychology, Tolman challenged the assumptions of behaviorism, including the notion that reinforcement was necessary for learning. At the same time, he sought to extend the framework to include more complex behaviors than the simple stimulus-response bonds that were central to early twentieth century behaviorism. He is most remembered for his studies of spatial learning in rats that led him to conclude that animals did not acquire a discrete set of responses but, rather, developed a cognitive map of their environment. His work led to neurological investigations of spatial information processing, provided a model for studying cognitive processes in humans, and helped extend the range of behaviors studied in nonhuman animals.