Irvin Rock (1922–1995) was an experimental psychologist who studied visual perception at the University of California at Berkeley. He wrote a book, titled The Logic of Perception, and was regarded as an excellent perceptionpsychologist. Rock is notable in the field of psychology for his 1957 experiment where he tilted a square to make it look like a diamond and then tilted his test subjects and asked them what shape they saw. The experiment tested Rock's hypothesis that perceptual phenomena could be explained by higher-level mental processes instead of merely by automatic processes. When his test subjects continued to perceive the shape as a diamond after being tilted to view the shape as a square, Rock concluded that perception is an intelligent, higher-level mental process. This differed from previous conclusions by Gestalt psychologists that perception was not a higher-level process.