Steven Arthur Pinker (born September 18, 1954) is a Canadian-American cognitive psychologist, psycholinguist, popular science author, and public intellectual. He is an advocate of evolutionary psychology and the computational theory of mind.Pinker is the Johnstone Family Professor of Psychology at Harvard University, and his academic specializations are visual cognition and developmental linguistics. His experimental subjects include mental imagery, shape recognition, visual attention, children's language development, regular and irregular phenomena in language, the neural bases of words and grammar, as well as the psychology of cooperation and communication, including euphemism, innuendo, emotional expression, and common knowledge. He has written two technical books that proposed a general theory of language acquisition and applied it to children's learning of verbs. In particular, his work with Alan Prince published in 1989 critiqued the connectionist model of how children acquire the past tense of English verbs, positing that children use default rules, such as adding -ed to make regular forms, sometimes in error, but are obliged to learn irregular forms one by one.