High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! Robert Boles aw Zajonc (Nov. 23, 1923 December 3, 2008) was a Polish-born American social psychologist who was known for his decades of work on a wide range of social and cognitive processes. One important contribution was the demonstration of the mere exposure effect, the phenomenon that repeated exposure to a stimulus brings about an attitude change in relation to the stimulus. His official faculty description notes that he focused on processes involved in social behavior, with an emphasis on the relationship between affect, or emotion, and cognition. Zajonc was also well known for demonstrating how social facilitation (how the presence of others increases or decreases performance) works in humans and other animals, notably in cockroaches, which indicated that social facilitation is not entirely the result of higher cognitive processes.