Arthur R. Jensen, an educational psychologist who ignited an international firestorm with a 1969 article suggesting that the gap in intelligence-test scores between black and white students might be rooted in genetic differences between the races, died on Oct. 22 at his home in Kelseyville, Calif. He was 89.

His death was confirmed by the University of California, Berkeley, where he was an emeritus professor in the Graduate School of Education.

Professor Jensen was deeply interested in differential psychology, a field whose central question — What makes people behave and think differently from one another? — strikes at the heart of the age-old nature-nurture debate.

Because of his empirical work in the field on the quantification of general intelligence (a subject that had long invited a more diffuse, impressionistic approach), he was regarded by many colleagues as one of the most important psychologists of his day.