Visual-preference and operant measures of infant memory

In three experiments with sixty 3- and 6-month-olds, we examined whether op erant and visual-preference measures of retention are equivalent. Infants l earned to move a mobile by kicking and then received a paired-comparison te st with the familiar (training) mobile and a novel one. Kicking above basel ine was the direct measure of retention, and longer looking at the novel mo bile was the visual-preference or inferred measure. Retention was tested 1 day after training (Experiment 1) or reactivation (Experiment 2) and immedi ately or 4 days after training (Experiment 3). Despite differences in age a nd retention interval, infants consistently, exhibited retention on the ope rant measure, but not on the visual-preference measure. These data reveal t hat the two measures of retention are not equivalent. When expectations are associated with a particular stimulus, infants indicate retention directly and robustly, rarely looking longer at a novel test stimulus. This result is not limited to operant situations. (C) 2001 John Wiley & Sons, Inc.