An expanding training series protracts retention for 3-month-old infants

This research examined whether an expanding training series protracts retention for infants as it does for children and adults. In three sessions spanning an 8-day period, 3-month-olds learned to move a crib mobile by kicking. Intersession intervals were either constant (1 or 4 days) or progressively expanding (average ISI = 4 days). The expanding-series group exhibited significant retention on a delayed recognition test 3 weeks after training was over, but the two constant-series groups exhibited none. Although the 1-day constant-series group remembered after 1 week, the 4-day constant-series group did not. Surprisingly, a reactivation treatment administered 4 weeks after training was over was ineffective whether infants were trained, reminded, and tested in a distinctive context or not. These results demonstrate that the retention advantage afforded by programming training sessions in an expanding series extends to infants and suggest that the upper limit on reactivation is timed from initial encoding and not from the point of forgetting.