The effect of multiple reminders on long-term retention in human infants

The present series of experiments compared the effects of single- and multiple-reminder procedures on the long-term memory of 3-month-old human infants. Subjects were trained for 2 consecutive days in the mobile conjugate reinforcement paradigm, and the reminder procedure (a reactivation treatment) was a brief, noncontingent exposure to the moving mobile. In Experiment 1, independent groups received one or two reactivation treatments during the 3 weeks following the conclusion of training. The last (or only) reactivation treatment occurred 20 days after training, and subjects were tested either 1, 3, 7, 14, or 22 days later (i.e., 21-42 days after the end of training). Although retention was equivalent following one or two reactivation treatments when testing occurred 1 day after the final (or only) treatment, subsequent retention was significantly prolonged by the second reactivation treatment; infants receiving a single reactivation treatment did not respond above operant level 7 days later, but infants receiving two reactivation treatments continued to respond for as long as 14 days (i.e., 34 days following the conclusion of training). Infants who received the reminders without prior training or who were trained but received no interpolated reminders performed at operant level during the long-term retention test. Furthermore, presenting a single reactivation treatment equivalent in duration to two treatments did not prolong retention.

In Experiment 2, retention was observed 14 days after the second reactivation treatment irrespective of whether the treatments were presented during the first and second or during the third and fourth weeks following the conclusion of training. Furthermore, although retention was not observed either 5 or 6 weeks after training following a single reactivation treatment presented for the first time after either 34 or 41 days, retention was observed after equivalent intervals following two reactivation treatments.

In Experiment 3, independent groups of infants received three reactivation treatments during the 3 weeks following training and were tested 1, 7, or 14 days later. Although retention was excellent when infants were tested 1 day later, retention was not better than that observed after a single reactivation treatment.