For decades, researchers have tried to understand how emotions are generated, expressed, and recognized. A variety of theories have emerged. At one extreme is the idea that emotions are the experience of physiological changes such as the increased heart rate that accompanies anger. Researchers at the other extreme see emotions as purely cognitive, merely another form of thought. Psychologists leaning toward the first concept tend to look for universal physiological changes that correspond to emotions (such as raised eyebrows when a person is surprised). Although they have had some success in identifying such universals, their studies have been thwarted by a variety of factors. The generation of emotions is apparently influenced by, among other factors, goals, diet, attitude, expectation, perception, and culture. Rules about the social display of emotion - such as its inappropriate to show anger - also influence its expression and make it difficult for researchers to link affective states with forms of expression. There is presently no widely accepted, comprehensive theory of emotions, although much has been learned.

It is clear, however, that emotions can be communicated - especially through music and various forms of bodily expression. Emotions can even be contagious. You may recall a favorite teacher who was so enthusiastic about a subject that you became interested in it too. Or, you may have watched an actor express an emotion so effectively that its impact, not only on the other characters in the drama, but also on the audience, was electrifying. Actors study posture, gestures, facial expressions, and vocal intonation to find the best ways to communicate their character's feelings. An effective actor is a master of affect.

An example of the impact of emotional expression occurs in the film Schindler's List when the one-armed Jewish machinest goes to thank Schindler for giving him a job. His face lights up when he sees Schindler and he leans toward him with dignity and gratitude: "I want to thank you sir for giving me the opportunity to work ... the SS beat me up, they would have killed me. But, I'm essential to the war effort thanks to you ... God bless you, sir. You are a good man ... God bless you." The sincere and grateful appreciation on the man's face clearly affects Schindler, and the viewer.This emotional scene becomes a turning point in the film, as we start to see Schindler's heart change.

Although emotion researchers have worked hard to uncover universal aspects of emotional behavior, few have explored emotions from the perspective of a person who knows another person well and can often guess his or her affective state. This is the approach available to HAL and the one we use to get to know another person. The key here is "get to know." HAL, working closely with a handful of people, can learn how each one of them expresses - or doesn't express - emotions under various circumstances. Once he becomes familiar with several individuals, he can discover commonalities in the ways they express emotions and perhaps use these discoveries to improve his recognition of affect in strangers. Nonetheless, to attain the best understanding of someone, he would have to get to know that person very well. In 2001, HAL is not only well acquainted with the Discovery 's crew, he is able to enjoy relationships with them, as he tells the BBC interviewer.

Reporter: HAL, despite your enormous intellect, are you ever frustrated by your dependence on people to carry out actions?

HAL: Not in the slightest bit. I enjoy working with people. I have a stimulating relationship with Dr. Poole and Dr. Bowman.