Jane S. Herbert

Memory retrieval by 18--30-month-olds: age-related changes in representational flexibility.

Deferred imitation was used to trace changes in memory retrieval by 18-30-month-olds. In all experiments, an adult demonstrated 2 sets of actions using 2 different sets of stimuli. In Experiments 1A and 1B, independent groups of infants were tested immediately or after a 24-hr delay. Each infant was tested with 1 set of stimuli from the original demonstration and 1 set of stimuli that was different. Recall of the target actions when tested with different stimuli increased as a function of age, particularly after a delay. In Experiment 2, infants were provided with a unique verbal label for the stimuli during the demonstration and the test. The verbal label facilitated performance by 24-month-olds tested with different stimuli but had no effect on performance by 18-month-olds. One hallmark of memory development appears to be an age-related increase in the range of effective retrieval cues for a particular memory.

Perceptual Training Prevents the Emergence of the Other Race Effect during Infancy

Experience plays a crucial role in the development of the face processing system. At 6 months of age infants can discriminate individual faces from their own and other races. By 9 months of age this ability to process other-race faces is typically lost, due to minimal experience with other-race faces, and vast exposure to own-race faces, for which infants come to manifest expertise [1]. This is known as the Other Race Effect. In the current study, we demonstrate that exposing Caucasian infants to Chinese faces through perceptual training via picture books for a total of one hour between 6 and 9 months allows Caucasian infants to maintain the ability to discriminate Chinese faces at 9 months of age. The development of the processing of face race can be modified by training, highlighting the importance of early experience in shaping the face representation.

The Ontogeny of Long‐Term Retention During the Second Year of Life

Developmental changes in retention were assessed in two experiments with 18- and 24-month-old infants. In both experiments, infants were tested in a deferred imitation paradigm. In Experiment 1, independent groups of infants were tested either immediately or after delays of 1, 14, 28 or 56 days. There was no age-related difference in the spontaneous production of target actions (baseline) or in immediate imitation. There were age-related changes in retention after longer delays. Eighteen-month-olds exhibited retention for 14 days and 24-month-olds exhibited retention for at least 56 days. In Experiment 2, the maximum duration of retention by 24-month-olds was assessed. Independent groups of infants were tested after 3 or 6 months. Infants exhibited some evidence of retention after 3 months; however, forgetting was complete after 6 months.

The ontogeny of human learning in delay, long-delay, and trace eyeblink conditioning.

The ontogeny of associative learning in delay (750-ms conditional stimulus [CS], 650-ms interstimulus interval [ISI]), long-delay (1,350-ms CS, 1,250-ms ISI), and trace (750-ms CS, 500-ms trace interval, 1,250-ms ISI) eyeblink conditioning was examined in 5-month-old human infants and adults. Infants and adults showed different acquisition rates but reached equivalent asymptotes of conditional responses (CRs) in standard delay conditioning. In long-delay and trace conditions, infants exhibited less robust conditioning than adults and minimal ability to appropriately time CRs. During infancy, the ISI, rather than the conditioning procedure, predicted rate and effectiveness of CRs. These findings suggest that higher order cognitive abilities begin emerging early in development. Across ontogeny, however, there are changes in the limits and parameters that support associative learning.

Timely sleep facilitates declarative memory consolidation in infants

Significance The potential benefits of infant sleep for memory processing are largely unexplored. Here we show evidence that having an extended nap (≥30 min) within 4 h of learning helps 6- and 12-month-old infants to retain their memories for new behaviors across a 4- and 24-h delay. These results suggest that infants rely on frequent naps for the formation of long-term memories. Human infants devote the majority of their time to sleeping. However, very little is known about the role of sleep in early memory processing. Here we test 6- and 12-mo-old infants’ declarative memory for novel actions after a 4-h [Experiment (Exp.) 1] and 24-h delay (Exp. 2). Infants in a nap condition took an extended nap (≥30 min) within 4 h after learning, whereas infants in a no-nap condition did not. A comparison with age-matched control groups revealed that after both delays, only infants who had napped after learning remembered the target actions at the test. Additionally, after the 24-h delay, memory performance of infants in the nap condition was significantly higher than that of infants in the no-nap condition. This is the first experimental evidence to our knowledge for an enhancing role of sleep in the consolidation of declarative memories in the first year of life.

Supporting Early Vocabulary Development: What Sort of Responsiveness Matters?

Maternal responsiveness has been positively related with a range of socioemotional and cognitive outcomes including language. A substantial body of research has explored different aspects of verbal responsiveness. However, perhaps because of the many ways in which it can be operationalized, there is currently a lack of consensus around what type of responsiveness is most helpful for later language development. The present study sought to address this problem by considering both the semantic and temporal dimensions of responsiveness on a single cohort while controlling for level of parental education and the overall amount of communication on the part of both the caregiver and the infant. We found that only utterances that were both semantically appropriate and temporally linked to an infant vocalization were related to infant expressive vocabulary at 18 mo.

Eye tracking infants : investigating the role of attention during learning on recognition memory

In the present study, eye tracker methodology was used to explore whether there were age-related changes in the focus of infant attention during a learning event and subsequent recognition memory for event features. Six- and 9-month old infants watched a video of an adult demonstrating a sequence of actions with an object while visual attention was recorded using an eye tracker. At both ages, attention was focused primarily on the object and person, with the background attended to for approximately 12% of their viewing time. Recognition memory for the person, object and background from the video was assessed immediately using a Visual Paired Comparison procedure. Despite focusing on the central features while watching the target video, infants showed only limited evidence of recognition memory for the individual components of the event. Taken together, these findings suggest that the early age-related changes in memory performance seen in the literature may not be the result of age-related changes in attentional focus during encoding.

The effect of language cues on infants' representational flexibility in a deferred imitation task.

Twelve- and 15-month-old infants who received simple verbal cues at encoding and retrieval exhibited superior representational flexibility on an imitation task compared to infants who did not receive those cues. Verbal cues can help early-verbal infants overcome perceptual dissimilarity and express knowledge in novel situations.

Visual recognition memory across contexts

In two experiments, we investigated the development of representational flexibility in visual recognition memory during infancy using the Visual Paired Comparison (VPC) task. In Experiment 1, 6- and 9-month-old infants exhibited recognition when familiarization and test occurred in the same room, but showed no evidence of recognition when familiarization and test occurred in different rooms. In contrast, 12- and 18-month-old infants exhibited recognition irrespective of testing room. Thus, flexibility across a change of room was observed at a younger age than flexibility across a change of background that has previously been seen with the VPC procedure (Robinson & Pascalis, 2004). To determine if limitations in representational flexibility across a change of background could be overcome by experiences during encoding, in Experiment 2, 6-, 9-, 12- and 18-month-old infants were familiarized with a picture on multiple backgrounds. At all ages, infants showed recognition across a change in background at test. These findings indicate that dissociating an item from its context during encoding may be an important factor in understanding the representational flexibility of visual recognition memory in infancy. Developmental changes in representational flexibility are likely driven by changes in the functional maturity of the hippocampal formation, and experience.

Infant and adult visual attention during an imitation demonstration

Deferred imitation tasks have shown that manipulations at encoding can enhance infant learning and memory performance within an age, suggesting that brain maturation alone cannot fully account for all developmental changes in early memory abilities. The present study investigated whether changes in the focus of attention during learning might contribute to improving memory abilities during infancy. Infants aged 6, 9, and 12 months, and an adult comparison group, watched a video of a puppet imitation demonstration while visual behavior was recorded on an eye tracker. Overall, infants spent less time attending to the video than adults, and distributed their gaze more equally across the demonstrator and puppet stimulus. In contrast, adults directed their gaze primarily to the puppet. When infants were tested for their behavioral recall of the target actions, “imitators” were shown to have increased attention to the person and decreased attention to the background compared to “non-imitators.” These results suggest that attention during learning is related to memory outcome and that changes in attention may be one mechanism by which manipulations to the learning event may enhance infant recall memory.