Robert Rosenthal, a psychologist renowned as an expert in nonverbal communication, and in particular what he called the “self-fulfilling prophecies” in which subtle, often unconscious, gestures can influence behavior, died on Jan. 5 in Riverside, Calif. He was 90.
His daughter Ginny Rosenthal Mahasin said he died in a hospital from an aneurysm.
Widely considered one of the leading social psychologists of the 20th century, Dr. Rosenthal, who spent much of his career at Harvard, was best known for his work in the 1960s on what he called the Pygmalion effect — or, more technically, “interpersonal expectancy.”
In one famous experiment, he gave an aptitude test to students at a California elementary school, then told teachers that a group of the students were set to “blossom” in the next year, while another one wasn’t. In fact, the two groups were selected at random, though the teachers didn’t know that.
A year later, he retested the students and found that those in the “blossom” group had gained an average of 27 I.Q. points, regardless of how they scored initially, while the other group performed much worse.
Dr. Rosenthal concluded that the students’ performance had been affected by the different ways teachers had treated the two groups, encouraging the first with extra help, positive reinforcement and warmer body language. He called it the Pygmalion effect after the Greek legend in which a sculptor falls in love with one of his works, bringing it to life.
“The bottom line is that if we expect certain behaviors from people, we treat them differently,” he told Discover magazine in 2015, “and that treatment is likely to affect their behavior.”
His 1968 book “Pygmalion in the Classroom,” co-written with Lenore Jacobson, the principal of the California school in the study, caused an uproar. Some social psychologists faulted his data. Albert Shanker, the head of New York City’s largest teachers’ union, condemned it for blaming educators.
But over the following decade, researchers accepted it as a model, and an inspiration. In 1978, Dr. Rosenthal and a Harvard colleague, the statistician Donald Rubin, analyzed 345 studies that drew on his original research, in settings as diverse as doctors’ offices, courtrooms and military training centers — and every one of them reaffirmed his findings.
“The same factors operate with bosses and their employees, therapists and their clients, or parents and children,” Dr. Rosenthal told The New York Times in 1986. “The more warmth and the more positive the expectations that are communicated, the better the person who receives those messages will do.”
In a related, earlier experiment, he applied his work to himself. As part of his dissertation at the University of California, Los Angeles, he found that the way he posed certain questions and behaved toward certain subjects had a significant impact on the outcome of a study, an effect he called “experimenter bias.”
He was at times critical of how his research could be simplified and distorted, especially by reformers in fields like education and medicine. There was no single toolbox of gestures, he said, that a teacher or doctor could use to improve results.
“It’s too simplistic to say that, for example, a physician is sending a message of rapport when he nods or tilts forward,” he told The Times. “When you freeze the moment and extract one part of what is going on from it, you lose the richness of the phenomenon.”
Robert Rosenthal was born on March 2, 1933, in Giessen, Germany, the son of Hermine (Kahn) and Julius Rosenthal, who sold clothing.
As the Nazis tightened their grip on Germany, the Rosenthals fled. They lived for a time in the British colony of Rhodesia, now Zimbabwe, before arriving in the United States.
They settled in Queens, but in Robert’s senior year they moved to Los Angeles, where his father opened a department store. Robert studied psychology at the University of California, Los Angeles, receiving his bachelor’s degree in 1953 and his doctorate just three years later.
Dr. Rosenthal’s training and early career was in clinical psychology, with a special interest in schizophrenia. But without his intending it to, his work began to take on a social angle.
While teaching at the University of North Dakota in the late 1950s, he conducted an experiment in which a group of students was given two sets of rats. He told the students that one set was trained to be adept at running a maze, the other was not — even though both were identically trained. He then had the students run the rats through mazes.
As he expected, the “maze bright” rats did significantly better. In a paper published in 1963, he concluded that the students had subconsciously favored the “maze-bright” rats in the way they handled them, giving them an advantage.
He married MaryLu Clayton in 1951. She died in 2010. Along with their daughter Ms. Mahasin, he is survived by another daughter, Roberta Rosenthal Hawkins; a son, David Clayton Rosenthal; and six grandchildren.
In 1963, Harvard hired Dr. Rosenthal on a short-term, nontenured basis to help replace Timothy Leary, a clinical psychologist who had been fired over his experimentation with LSD and other drugs.
A year later, he was offered a tenured job in a different field, social psychology, beating out a promising social psychologist named Stanley Milgram. Dr. Rosenthal suspected that it was because Dr. Milgram was quickly gaining notoriety for a series of now-famous experiments showing how easy it was to get one person to administer electric shocks to another, and that Harvard was wary of promoting him.
In addition to his work on experimenter bias and interpersonal expectations, Dr. Rosenthal was a pioneer in meta-analysis, in which he developed a framework for combining multiple studies of the same phenomenon to reach better results.
Dr. Rosenthal retired from Harvard in 1999, then moved to the University of California, Riverside, where he taught until 2018.
He retired from that job when his usually stellar evaluations by students began to decline, to just above average, he wrote in “Pillars of Social Psychology,” a 2022 book edited by Saul Kassin.
“Listening to the data,” he added, “I went to the department chair that week and announced that I’m retiring.”