Unaware learning versus preserved learning in pharmacologic amnesia: similarities and differences.

The differences between learning in lorazepam (LOR)--or scopolamine (SCOP)--induced amnesia and learning in unaware drug-free normal subjects were examined. The drugs produced impairment in free recall, but did not affect digit span or word retrieval. In a verbal version, but not a motor version, of the serial reaction time task, the subjects who received SCOP or higher dose LOR showed impairment of sequence-specific learning. Subjects who received placebo had no such impairment. In the stem completion paradigm, higher dose LOR, but not SCOP, impaired performance. In a tachistoscopic word identification task, neither drug interfered with repetition priming. Unaware learning and drug-induced amnesic learning were thus dissociable. These findings disconfirm the hypothesis that unaware learning and drug-induced amnesic learning are analogous.