Perceptual constraints on infant memory retrieval.

In three experiments with 78 3-month-olds, we asked what determines whether or not a stimulus will pop out and cue retrieval from long-term memory. All infants were trained with mobiles displaying either Qs (feature-present stimuli) or Os (feature-absent stimuli) and were tested 24 h later. When the diagonal line of the Q bisected its rim, feature-absent stimuli controlled retrieval in tests with homogeneous displays, and stimulus novelty controlled retrieval in tests with pop-out displays. A follow-up experiment revealed that the similarity between Q and O determined whether or not Q popped out: When its tail projected externally from the rim, Q popped out and cued retrieval, but O did not (search asymmetry). When its tail projected internally from the rim, however, 3-month-olds failed to discriminate Q from O (the externality effect). These data reveal that target-distractor similarity constrains whether or not a feature-present stimulus will pop out and cue retrieval.