"In the first study, nursery school children watched an adult heaping verbal and physical abuse on an inflatable Bobo the clown doll..."

"... punching it in the nose, kicking it, hitting it on the head with a mallet and throwing it around the room. When the children were then given a chance to interact with a similar doll, they copied the adult’s abusive behavior and produced additional forms of abuse that they thought up on their own. In contrast, children who watched an adult interacting peacefully with the doll, or who were not shown a model at all, were significantly less aggressive.... Later studies indicated that just showing a film of an adult acting aggressively could produce similar results. And the children’s response to the adult model could be influenced by whether the aggressive behavior was rewarded or punished.... The results of the Bobo doll experiment were at odds with behaviorism and conflicted with the reigning mental health theory of the time, psychoanalysis, which held that vicarious aggression — watching a violent film, for example — would provide a catharsis, diminishing the need to act out aggressive impulses."

From "Albert Bandura, Leading Psychologist of Aggression, Dies at 95/He was most known for his Bobo doll experiment, in which children mimicked adults in attacking an inflatable doll. The work challenged basic tenets of psychology" (NYT).