Professor George Miller, from Princeton University, explains what psychology is, what psychologists do, and the importance of the Second World War to the study of human behaviour.

Professor Jerome Bruner, from the New School for Social Research in New York, explains how the study of the 'mind', once a dirty word in psychology, has revolutionised the exploration of our mental lives. He also discusses insights into the growth of the infant mind and describes some of his own work with children.

Until the present century vision was often regarded as a simple process - the eyes provide the brain with pictures of the outside world, and the brain just looks at them. We now know that visual perception is one of the most complicated functions that the human brain performs. Professor Richard Gregory, from the University of Bristol, shows how the study of illusions has demonstrated how much of what we see ' out there' is actually generated from within.

Until recently psychologists shunned questions about the philosophy of 'mind' in the belief that they were tedious and unanswerable. Professor Daniel Dennett , from Tufts University in Boston, describes how the study of computers and artificial intelligence has helped philosophy and psychology to enjoy a more fruitful relationship.

One of Sigmund Freud's most important contributions to psychology was the notion of an unconscious mind which can guide our behaviour in curious and unexpected ways. This has not only given rise to a whole new branch of psychiatric treatment - psychoanalysis - but has transformed the way in which people think about .themselves and their actions. Stuart Hampshire, Warden of Wadham College, Oxford, discusses the significance of Freud's 'discovery'.