Memory

Evidence for these components comes from several sources, including studies of brain-damaged patients with specific deficits in working memory. For example, stroke patients with lesions in the left temporoparietal areas often have selective impairments of the speech-based component, whereas patients with right-hemisphere damage often exhibit selective impairments of the imagery component.

Historically, most research on memory has focused on people's conscious, intentional recollection of previous experiences. This "explicit" memory is involved when we remember what we had for dinner last night, recollect what we saw at the movies last week, or reminisce about adventures with an old high school friend.

Over the past 10 years, however, research has developed on unconscious or "implicit" memory, in which people's past experiences affect their present perceptions and judgments without their awareness or voluntary control. Much recent evidence indicates that explicit and implicit memory are separate. For example, implicit memory is often left intact even when explicit memory is profoundly impaired by brain injury. Researchers have also explored implicit memory in patients with dissociative disorders such as multiple personality, who have several "ego states," each associated with different autobiographical memories. Surprisingly, im-plicit memories transfer across the patients' many personalities even if explicit memories do not.

Patients suffering severe amnesia due to brain damage cannot explicitly recollect the items presented in a list of words, but tests show that their implicit memory is intact. Such findings suggest that implicit and explicit memories are supported by different brain structures, only some of which are damaged in patients with amnesia.

The sparing of implicit memory may provide an initial avenue for therapies designed to recover memory and reintegrate personality. Basic research on implicit memory has already yielded novel approaches to the practical issue of rehabilitating memory in people with amnesia resulting from brain injury or disease. In several studies, conditioning procedures based on implicit memory were used to teach such patients relatively complex skills, such as computer programming, which enabled them to gain employment.

The Cognitive Unconscious

The study of implicit memory provides a general framework for thinking about how unconscious memories of past events influence current experience, thought, and action. As one example, laboratory experiments have shown that people's preference for abstract art can be increased by exposures to it that they cannot consciously remember. These effects occur even when the artworks are initially presented subliminally. To carry matters one step further, in one study, subliminal presentation of faces led subjects to interact more with the actual people depicted an unconscious influence on their social behavior.