Implicit Memory

The term memory is typically used to refer to conscious recollection of past events, a state in which current mental contents are recognized as a product of prior experience. However, researchers have long supposed that memory for the past can influence present behavior without conscious recollection. The Swiss neurologist Édouard Claparède provided a famous example in his study of a patient with Korsakoff's syndrome, a disease resulting in amnesia. This patient had great difficulty remembering new events that occurred after the onset of the disease. Claparède suspected, however, that the patient had residual memory abilities that did not produce conscious recollection. To test this possibility, Claparède hid a pin in his hand and gave the patient a painful pinprick on shaking hands. When Claparède next met the patient, she refused to take his offered hand. When asked for an explanation, the patient could not provide a reason for her refusal to shake hands. When pressed, she said that people sometimes hide pins in their hands as a type of practical joke. Clearly the patient formed some type of memory of the original event, but this memory was not recollected as a personal experience. Hermann Ebbinghaus, in his pioneering analysis of memory, similarly argued that memories for past events could influence behavior without conscious recollection, a view that prompted the development of the savings measure of memory.

Modern research in psychology, neuropsychology, and neuroscience supports a distinction between conscious and unconscious influences of memory, embodied in the distinction between explicit and implicit memory. Explicit memory refers to intentional or conscious recollection of prior experiences. Implicit memory, in contrast, refers to influences of the past that are not accompanied by intentional or conscious recollection. This entry describes how these two forms of memory differ from one another. It also describes the major theories accounting for these differences, and reviews recent neuroimaging studies that delineate the brain regions underlying explicit and implicit memory.