Exemplar spacing and infants' memory for category information

In novelty preference studies of categorization, all exemplars are exposed within a single session, and category information is retained for only a few minutes. In mobile studies of categorization, one exemplar is exposed per day, and category information is retained for many days. In five experiments, we asked if exemplar timing affects this retention difference by exposing infants in the mobile paradigm to all category exemplars within each session. Three-month-olds did not recognize a novel category member after 24 hours (Experiment 1) because they did not acquire the category when exemplars were massed (Experiment 2). Six-month-olds recognized a novel category member after 24 hours when the daily exemplar order was random (Experiment 4), and both ages recognized the individual exemplar from Serial Position 1 after 24 hours when the daily exemplar order was constant (Experiments 3 and 5). As a rule, greater spacing between successive items protracts retention. This factor appears largely responsible for paradigmatic differences in infants' long-term memory for category information.