Carolyn Rovee-Collier

The Development of Infant Memory

Over the first year and a half of life, the duration of memory becomes progressively longer, the specificity of the cues required for recognition progressively decreases after short test delays, and the latency of priming progressively decreases to the adult level. The memory dissociations of very young infants on recognition and priming tasks, which presumably tap different memory systems, are also identical to those of adults. These parallels suggest that both memory systems are present very early in development instead of emerging hierarchically over the 1st year, as previously thought. Finally, even young infants can remember an event over the entire “infantile amnesia” period if they are periodically exposed to appropriate nonverbal reminders. In short, the same fundamental mechanisms appear to underlie memory processing in infants and adults.

The Development of Implicit and Explicit Memory

This is the only book that examines the theory and data on the development of implicit and explicit memory. It first describes the characteristics of implicit and explicit memory (including conscious recollection) and tasks used with adults to measure them. Next, it reviews the brain mechanisms thought to underlie implicit and explicit memory and the studies with amnesics that initially prompted the search for different neuroanatomically-based memory systems. Two chapters review the Jacksonian (first in, last out) principle and empirical evidence for the hierarchical appearance and dissolution of two memory systems in animal models (rats, nonhuman primates), children, and normal/amnesic adults. Two chapters examine memory tasks used with human infants and evidence of implicit and explicit memory during early infancy. Three final chapters consider structural and processing accounts of adult memory dissociations, their applicability to infant memory dissociations, and implications of infant data for current concepts of implicit and explicit memory. (Series B)

Time windows in cognitive development.

The problem of integrating new information with old is fundamental to the development of cognition. The solution to this problem underlies establishment of the knowledge base, learning, category formation and expansion, the modification and selective strengthening of memories, language acquisition, access to information after very long intervals, and individual differences in a number of different domains. This article introduces a new construct, the time window, that characterizes when and how such integration occurs. It describes the characteristics of time windows, evidence for them, factors that affect them, research illustrating their generality, and their theoretical and applied implications

The Economics of Infancy: A Review of Conjugate Reinforcement

Publisher Summary Conjugate reinforcement has been used successfully with both normal and impaired organisms of all ages. It programs a variety of reinforcing consequences, both social and nonsocial, in a manner that simulates the natural patterns of interaction between organisms and their environments. With infants it has been particularly successful, sustaining high and stable response rates for relatively long time periods. This has made possible the use of individual baselines in addition to the use of standard control groups. It has also permitted more reliable observations of the short- and long-term influences of the independent variables than have been possible with either episodic schedules or techniques, which do not rely on motivated behavior. Further, the rapidity with which even the youngest infants acquire conjugately reinforced responses has eliminated the necessity for lengthy shaping or training periods. A major requirement of the free-operant method is that the response be a recurrent behavior, which can be produced over long periods without fatigue. The main limitation that the conjugate paradigm imposes upon the selection of responses and reinforcers is that they be sufficiently variable to permit the infant to discover the proportionality relationship between them.

Topographical response differentiation and reversal in 3-month-old infants

In two experiments spontaneous topographical response differentiation was assessed in twenty-eight 3-month-old infants during free-operant conditioning. In Experiment 1, 15 infants were tested in the laboratory for a single session. Activity of all limbs produced somesthetic feedback, but only movement of the right leg produced visual conjugate reinforcement (mobile movement). Response localization was exhibited early in acquisition when leg activity exceeded arm activity, but specific differentiation between legs did not occur until the first extinction period when the right leg significantly dominated the left. Arm activity, as well as activity of all limbs of a noncontingent control group, remained unchanged throughout the session. In Experiment II, 13 infants were tested in their home cribs for successive days. All exhibited rapid and stable differentiation between legs, and 4 of 5 exhibited rapid and complete reversal of leg dominance when control of the mobile action was shifted to the other leg. The phenomenon was interpreted in terms of the optimization principle.

Contextual Constraints on Memory Retrieval at Six Months.

In 3 experiments, 6-month-old infants learned to move a mobile by kicking and were tested 1 to 21 days later for retention of the newly acquired memory as a function of the training and testing contexts. In Experiment 1, decreasing the relative distinctiveness of the training and testing context did not impair retrieval of the newly acquired memory. In Experiment 2, however, testing in a different context completely eliminated retention after delays of 1 and 3 days, when retention was otherwise perfect; after progressively longer delays, retention improved paradoxically. The familiarity or novelty of the test context was not a factor in the failure of infants to recognize the mobile in the altered context after 1 day. In Experiment 3, the effect of an altered context was assessed in a reactivation paradigm. After the training memory was forgotten, infants were presented with the original mobile as a reminder and were tested for retention of the training memory 1 day later. When either the reminding context or the testing context was different, they exhibited no retention. These findings reveal that memory retrieval at 6 months is highly specific to the setting in which the memory is acquired. We propose that infants learn what specific events are associated with what specific places prior to the age when they can locomote independently and acquire a spatiotemporal map of the relations between those places.

Contextual determinants of retrieval in three-month-old infants☆

Abstract Three-month old infants learned to kick to produce movement in an overhead crib mobile on a conjugate reinforcement (FRI) schedule. All infants were trained in the presence of one of two distinctive crib bumpers. In Experiment 1, infants receiving cued-recall tests in the presence of the original training bumper remembered the conditioned association 1 week later, but those tested in the presence of a different bumper did not. Two weeks later, neither training group evidenced retention of the contingency. In Experiment 2, infants who received a 3-min exposure (“a reactivation treatment”) to the original training bumper 24 h prior to the 2-week retention test exhibited excellent long-term retention, whereas those exposed to a different bumper as a reminder did not, irrepective of whether it was identical to the test bumper or not. These findings demonstrate that the context alone, even though it was never exclusively paired with reinforcement, can act as a retrieval cue.

Ontogeny of early event memory: II. Encoding and retrieval by 2- and 3-month-olds.

Abstract The ability of 2-month-old infants to discriminate changes in a 5-object crib mobile following a retention interval of 24 hr was assessed using the mobile conjugate reinforcement paradigm. Infants were trained in 3 daily 15-min sessions to produce mobile movement by footkicking. Twenty-four hr later, independent groups received generalization tests with mobiles containing 1–5 novel objects substituted into their original training mobile. A control group was tested with the original training mobile. These findings were compared with findings of 2 previous studies involving identical procedures with 3-month-olds, reanalyzed for measures of individual performance over successive test minutes. Although, in absolute terms, 2-month-olds had a flat generalization gradient relative to 3-month-olds, when each infants kick rate during the generalization test was expressed relative to that infants kick rate before, and at the end of, training, it was found that the generalization gradients of 2- and 3-month-olds were indistinguishable. The relative response measures indicated a surprising degree of specificity by both age groups: Test mobiles containing more than 1 novel object did not cue retrieval, but test mobiles containing no more than 1 new object yielded perfect retention and complete generalization. These data indicate that infants as young as 2 months are capable of encoding and maintaining a representation of the specific details of their training context for at least 24 hr and, after that delay, can perform fine discriminations based on the discrepancy between their test context and that representation.

The ontogeny of long-term memory over the first year-and-a-half of life

This research documents the development of long-term memory in human infants from 2 months through the end of the first year-and-a-half of life. In the initial study phase, we trained 6- to 18-month-old human infants in an operant task and tested them after increasing delays until they exhibited no retention for 2 successive weeks. In the second phase, their data were combined with data previously obtained from 2- to 6-month-olds in an equivalent task. The resulting function revealed that the duration of retention increases monotonically between 2 and 18 months of age. This increase was not due to age differences in original learning. This is the first systematic analysis of the course of long-term memory across an extended period of infant development that is based on standardized parameters of training and testing. It provides a reference function against which measures of retention from infants of different ages that are obtained in different memory tasks with different parameters can be meaningfully compared.

A conditioning analysis of infant long-term memory.

The long-term retention of conditioned operant footkicks by 3-month-old infants was assessed in 2 studies. In both, infants were trained in a conjugate reinforcement paradigm in which footkicks produced conjugate activation of the components of an overhead crib mobile. After 2 training sessions, retention (cued recall, savings) was assessed cross-sectionally in a third session scheduled after varying intervals. In experiment 1, 32 infants were tested after intervals of 48, 72, 96, or 120 hours; in experiment 2, 24 infants were tested after 96, 144, 192, or 336 hours. No evidence of forgetting was observed for as long as 192 hours following original training. Although both retention measures indicated a significant memory deficit in the group tested after 336 hours (2 weeks), some individuals continued to exhibit substantial recall and savings after this retention interval. A conditioning analysis was viewed as a logical means by which to bridge the gap between animal and adult human models of memory.