When David Marr at MIT moved into computer vision, he generated a lot of excitement, but he hit up against the problem of knowledge representation; he had no good representations for knowledge in his vision systems.
Bio: Martin E. P. "Marty" Seligman is an American psychologist, educator, and author of self-help books. Since the late 90's, Seligman has been an avid promoter within the scientific community for the field of positive psychology.