Building a memory representation in the first year of life: The effect of repeated exposure on memory specificity in 9-month-olds

Although the ability to recall information over the long term emerges in the second half of the first year of life, mnemonic capabilities are fragile and unreliable at this time. We suggest that repeated exposure to to-be-remembered events may be one means of facilitating long-term memory in infancy: as is suggested in some computational models of memory, increased exposure might strengthen initially weak memory representations through the addition of stimulus-specific detail. In the present study, we investigated the potential facilitative effects of repeated exposure on the formation and maintenance of strong, detailed memory traces using electrophysiological assessments of recognition memory (event-related potentials: ERPs) and behavioral measures of recall (deferred imitation). In a between-subjects design, infants witnessed the presentation of 2-step sequences one, two, or three times before a recognition memory test designed to assess the strength of the encoded representation. During the recognition test, infants were presented with photographs of familiar sequences, perceptually distinct, functionally identical analogues, and completely novel items. Infants allowed three exposures to the stimuli participated in another recognition memory assessment 1 week after the first and a delayed recall memory test 1 month thereafter. Infants showed evidence of having encoded the familiar sequences. Effects of repeated exposure indicated that infants allowed more exposures processed familiar items more quickly than infants allowed fewer demonstrations; infants allowed only one exposure processed photographs of familiar items more slowly than novel ones. There was no evidence of differential processing involving the analogue stimuli, which suggested that repeated exposure did not facilitate the formation of more specific, detailed representations in the expected manner. However, the results indicate that infants realized the familiar and analogue items were distinct, as patterns of recall memory differ from those obtained in our previous investigations, which included only familiar and novel stimuli. We suggest that infants may have noticed the perceptual differences between familiar and analogue items, but that this realization did not influence their conceptual processing of them. Future research directions pursue relations between perceptual and conceptual categorization and recognition and recall memory in infancy.