Implicit memory and semantic learning in post-traumatic amnesia.

Implicit and explicit memory performance, and new semantic learning in post traumatic amnesic (PTA) patients were assessed in two experiments. The first experiment compared implicit and explicit memory for word lists for eight PTA patients and matched controls. Subjects participated in one implicit memory test (stem completion) and three explicit memory tests (stem-cued recall, free recall, and old/new recognition). PTA patients showed intact priming on the stem completion task, while performing significantly worse than control subjects on all three explicit memory tests. The second experiment examined new semantic learning in PTA patients. The method of vanishing cues, developed by Glisky, Schacter and Tulving (1986), was used to teach five fictitious facts (e.g. Bob Hope's father was a fireman) to four PTA patients and four matched controls. Despite variability among the PTA patients, they showed substantial learning within the PTA state and good retention 5 days and several weeks following the emergence from PTA. These studies suggest that implicit memory abilities are preserved in PTA patients, and that these patients are able to learn new semantic information despite their profoundly impaired explicit memory performance