Verbal memory improved by D-amphetamine: influence of the testing effect.

OBJECTIVE The improvement of long-term retention of verbal memory after an acute administration of D-amphetamine in recall and recognition tasks has been ascribed to an influence of the drug on memory consolidation. Because recent research has demonstrated that intermediate testing is of overriding importance for retention, we investigated whether D-amphetamine modulates the repeated testing effect in verbal long-term recognition. METHOD Forty men participated in two double blind placebo controlled studies. In Experiment 1, we manipulated the number of recognition tests and in Experiment 2, we compared repeated with nonrepeated testing of the same items. RESULTS Drug effects were observed on delayed tests only, leaving immediate recognition unaffected. Number of intermediate recognition tests and repeated testing of the same items were not affected by D-amphetamine. CONCLUSIONS We conclude that the D-amphetamine memory enhancement is not related to the testing effect. This result supports that D-amphetamine modulates other aspects of the consolidation process, probably related to context effects.