Esther Thelen, 63, a prominent developmental psychologist who studied how the brains of human babies help them move, learn and generally function, died Dec. 29 at a hospital in Bloomington, Ind. She had cancer.
Based at Indiana University, Dr. Thelen was a psychology professor and director of the university's Infant Motor Development Laboratory. She and colleagues studied infant movement, perception and cognition and how perceptual motor skills in infancy can say much about how people will adapt later in life.
Her work at Indiana University, and before that at the University of Missouri, has been credited with presenting a new view of how babies learn to reach for toys, walk and accomplish some of the earliest mental tasks, such as remembering where things are.
For years, most researchers believed that infants reached and walked when parts of the brain responsible for these activities "matured." But based on 19 years of research, Dr. Thelen believed that these accomplishments reflect a complex interplay of factors that includes babies' changing bodies and their external environments, as well as their growing brains and nervous systems.
"Babies are constantly trying to figure out things like 'How am I going to look around?' and 'How am I going to see that nice smiley face?' " Dr. Thelen told Indiana University's Research & Creative Activity journal in spring 2003. "I believe the behavior we see is not residing somewhere in the brain. Instead, it emerges in the movement."
Mixing theory with experiment, Dr. Thelen applied what is known as dynamic systems theory -- popularized under the name "chaos theory" -- to gain an understanding of the overall behavior of a system.
Her work has influenced scholars in psychology, kinesiology, cognitive science, computer science, robotics and neuroscience.
Esther Stillman Thelen was a native of Brooklyn, N.Y., and a 1964 zoology graduate of the University of Wisconsin. She then received a master's degree in zoology and a doctorate in biology, both from the University of Missouri, where she taught psychology until moving to Indiana University in 1985.
She held visiting faculty roles at Ben Gurion University in Israel and l'Ecole des Hautes Etudes en Sciences Sociales in Paris, among other universities.
She was a fellow of the American Association for the Advancement of Science and the American Psychological Association and was president of the Society for Research in Child Development.
She contributed to more than a dozen journals in psychology, child development and motor neuroscience. She also wrote or contributed to a handful of texts.
Survivors include her husband, David P. Thelen, whom she married in 1962, of Bloomington and Lakeside, Mich.; two children, Jennifer Thelen of Richmond, Calif., and Jeremy Thelen of Providence, R.I.; a sister; and a grandson.