Abstract A slide with 8 geometrical shapes was projected for 3 min to 787 students who were instructed to draw during the following 2 min what they remembered. From the students correctly reproducing 5–7 items (average performance) 70 were selected for further experiments. On Day 1, all subjects were shown a similar set of geometrical shapes. Retrieval was tested immediately and in 2 or 5 consecutive sessions at 48 hr intervals. Drugs (amphetamine 20 mg of amobarbital 200 mg) or placebo were administered 30 min before learning or retention testing. Control groups took placebo, amobarbital or amphetamine in all sessions whereas in the experimental groups these were alternated from session to session. Similar results were obtained both in the three and six sessions experiments. In all control groups the same monotonic forgetting curves were observed. In the experimental groups, regardless of whether the change was from drug (amphetamine of amobarbital) to placebo or from placebo to drug, retrieval was impaired in the second, fourth and sixth session and improved in the third and fifth session. The same results were observed with either drug.
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