Actors who throw themselves into a role requiring a display of powerful emotion often claim that the feigned feeling quickly becomes real.

Now a psychiatrist has found that many people experience the same reaction, becoming genuinely angry, for example, when they meant only to fake a brief display, or becoming deeply saddened when they meant only to show a bit of empathy.

In fact, the researcher has found, the same effect can occur in people who are merely instructed to move certain facial muscles in a way that produces the facial expression appropriate to the emotion.

"By making a face, you can create an emotion," said Paul Ekman, a psychiatrist at the University of California, San Francisco.

Ekman was encouraged to undertake the study by the late Lee Strasberg, the acting teacher known for the "Method" style in which an actor strives for close personal identification with a role. Ekman presented his findings Tuesday at the annual meeting of the American Association for the Advancement of Science.

Somehow, Ekman speculated, nerves from the engaged facial muscles communicate with regions of the conscious brain that are responsible for generating emotions in the more traditionally accepted way.

He said it was as if activating any part of the nerve network responsible for an emotion resulted in activating the whole network.

Volunteers in Ekman's experiments were not told the name of the emotion they were to display. Instead, they were told to move various facial muscles.

For example, to produce an angry face, the volunteers were instructed to combine the following actions: raise the eyebrows, pull the eyebrows together, raise the upper eyelids, tighten the lower lids, drop the jaw, and stretch the lower lip wide. Separate tests showed that most people could not identify the intended emotion on the basis of the instructions.

However, within seconds of carrying out the instructions, volunteers not only recognized the emotion but reported that they felt it strongly. Electronic monitors of brain waves, heart and breathing rates, and other physical responses like those measured in lie detector tests revealed patterns of reactions typical of people in whom the same emotion was elicited in conventional ways.

Ekman said similar findings applied to such other emotions as fear, disgust and sadness. He said there is also preliminary evidence for the same effect with the emotions of surprise and contempt.

However, Ekman said he was surprised and disappointed to find that happiness could not be produced by making a smiling face.

The muscle actions appropriate to various emotional expressions have been known for many years. In fact, Charles Darwin determined about half of them when researching one of his later books that suggested that patterns of facial expression of emotion evolved in ancient times and are innate.

Darwin's speculation has been supported by anthropological studies showing that most facial expressions are readily recognized as having the same meaning in all cultures.