Leon J. Kamin (December 29, 1927 – December 22, 2017) was an American psychologist known for his contributions to learning theory and his critique of estimates of the heritability of IQ. He studied under Richard Solomon at Harvard and contributed several important ideas about conditioning, including the "blocking effect". Early life and education Leon Kamin was born into a Jewish family in Taunton, Massachusetts; his father was a rabbi. Kamin studied psychology at Harvard. While a Harvard undergraduate, he joined the Communist Party, but dropped out of the party by 1950 and became a Harvard graduate student and teaching fellow. While a graduate student, Kamin was subpoenaed by the Jenner anti-Communist Senate committee, but he refused to name others who had been (or might have been) Communists and cited his Fifth Amendment rights. As a result, Harvard refused to renew his fellowship. Next, Joe McCarthy's anti-communist committee came to Boston, looking for Communists and ex-Communists. Refusing to names, Kamin was convicted of contempt of the Senate. This caused job offers in the U.S. to dry up and he had to find employment in Canada, where held positions, first at McGill University, then at Queen’s University and McMaster University (where he chaired the Psychology Department in 1957–58). In 1968 he returned to the U.S. and chaired Princeton University's Department of Psychology and later the Psychology Department at Northeastern University in Boston, Massachusetts. Career Kamin's most well-known contribution to learning theory was his discovery and analysis of the "blocking effect" (1969). He showed that conditioning an animal to associate a salient conditioned stimulus (CSb), such as a bright light, with a salient unconditioned stimulus (US), like a shock, is "blocked" when CSb is presented simultaneously with another conditioned stimulus (CSa) that was already conditioned to the US. (Kamin used rats in most of his research, but the effect has been found in many animals). However, a 2016 article in the Journal of Experimental Psychology: General reported "15 failures to observe a blocking effect despite the use of procedures that are highly similar or identical to those used in published studies." In March 1972 an invitation from the Princeton Psychology Department (which Kamin chaired at the time) to Richard Herrnstein (who had a few months earlier published a contentious article about race, gender, class, and intelligence) sparked a major controversy and threats of protest. Herrnstein canceled his visit, saying that "It would be