Robert Rosenthal, a psychologist renowned as an expert in non-verbal communication, and in what he called “self-fulfilling prophecies” in which subtle and often unconscious gestures can influence behavior, died on Jan. 5 in Riverside, CA. He was 90.

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 on what he called the Pygmalion effect, concluding that performance is enhanced when given positive reinforcement.

In addition to his work on 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.