Robert Zajonc’s was probably best known for his work finding situations in which emotion, rather than cognition, seems to lead behavior. Sometimes the effect was entirely unknown to the person engaged in the behavior. For instance, there was the “mere exposure effect,” in which people prefer objects they have previously seen, often so fleetingly that they cannot consciously recall having seen them. He also demonstrated a small relationship between birth order and IQ; and he found that experts are facilitated by the presence of onlookers, but novices are hindered by them; and he controversially theorized that emotional facial expressions actually control the flow of blood to regions of the brain responsible for emotional feeling.
A surviver of the Nazi invasion of Poland as a young man, Zajonc earned a PhD at U. Michigan in 1955, where he remained for most of his career. He died of complications related to pancreatic cancer. He was 85. The full New York Times obituary is here.