Developments in early recall memory: normative trends and individual differences

Declarative memory in abused and neglected infants

To summarize, all children interacted with the experimenter and actively participated in the imitation task. There was evidence of improvement in performance from baseline to recall as would be expected with attention to, and memory for, the actions that were modeled by the experimenter. All participants evidenced a decrease in performance as the difficulty of the task increased, as would be expected. When the maltreated children were compared to the nonmaltreated children in a 2-group design, there was no statistically significant difference in performance. However, when the maltreated group was divided into two subtypes of either neglected or abused, and performance was compared in a 3-group design, it was revealed that the neglected children experienced deficits in performance relative to abused children. For production of target actions, the neglected children's performance trended toward significance when compared to the nonmaltreated children's performance. However, there was no significant difference between the performance of the abused children and the nonmaltreated children for either production of target actions or productions of ordered pairs. The children in this longitudinal study were assessed previously at 12 months of age in a mother-child play situation (Valentino et al., 2006). Interactions during structured play between mother and child were evaluated for maternal directives and child responses. Interestingly, the difference in social interactions that was most reliable was the finding that the abused children imitated their mothers more often than did the nonmaltreated children. There was no difference between the imitative behaviors of the neglected children and the abused or nonmaltreated children. The researchers note that by imitating their mothers, the abused children might be attempting to prevent further abusive incidents. Limit setting behaviors of the mothers in response to child initiations were positively related to the children's imitative behaviors. Thus, it would appear that maternal negative feedback to child-initiated behaviors is related to an increase in imitative behaviors that are most likely met with positive reinforcement. The continued pursuit of this positivity may impede the development of self-initiated behaviors; delayed development of self-initiated behavior has been linked to disorders of social competence (Landry, Smith, Miller-Loncar, & Swank, 1998). However, imitation has long been known to be a mechanism of learning (Piaget, 1962) and has become an accepted tool for assessment of declarative memory (Bauer, 2004). Whereas the adaptation to abuse posited by Valentino et al. (2006) may be detrimental to social development, our data for this same sample indicate that the reliance on imitative behavior exhibited by the abused children may afford them an advantage at 21 months of age in imitation paradigms. The neglected children are thus at a disadvantage relative to the abused children in the study reported here in that they were not reinforced by mothers for imitative behavior. It is important to note that all children in this sample were from low-income homes. Scores on these events for both target actions and ordered pairs are higher in samples of higher SES children (e.g., Bauer et al., 2000). Thus, the low SES of the families affected performance across the groups. It is possible that the factor responsible for the difference between the abused group and the neglected group is resilience in the face of poverty. Resilience is the ability to recover following a traumatic event or adversity (Masten, 2001), and has been related to child characteristics, such as general intelligence (Masten et al., 1988). It has been proposed that neural plasticity may be responsible for this recovery (Cicchetti & Curtis, 2006). Alternatively, as has been detailed earlier in this chapter, the advantage afforded abused children could arise from the strengthening of neural pathways. It would be adaptive to develop exceptional event memory so as to avoid the events that lead to abuse. Mechanisms of plasticity are responsible for the laying down of memories (Aimone, Wiles, & Gage, 2006). Thus, the higher performance seen in the abused group could be related to a preservation of brain plasticity that facilitates resilience in the face of poverty, stress, and/or trauma. Plasticity in the brains of the neglected children may be lost due to the lack of stimulation, leaving them more vulnerable to the stress of poverty and neglect. In conclusion, maltreated children have often been studied as a single group. However, it is becoming clear from research conducted by our group and others that the subtypes of maltreatment may have different developmental sequelae. It is important that we understand the differential pathways involved in the development of abused versus neglected children. As discussed in other chapters of this volume, the imitation paradigm has emerged as a valuable tool in the identification of at-risk infants and toddlers. With the data reported here, it is evident that data from the elicited imitation procedure utilized herein differentiates between the subtypes of maltreatment. Research must be conducted to further elucidate the correlates of resilience in toddlers who have been abused. A longitudinal investigation would enable investigation of the questions of continuity of the observed increase in imitative behavior and whether increased imitation has a detrimental social effect while exerting a bolstering cognitive effect.

The development of children's early memory skills

A multitask battery tapping nonverbal memory and language skills was used to assess 60 children at 18, 24, and 30 months of age. Analyses focused on the degree to which language, working memory, and deliberate memory skills were linked concurrently to children's Elicited Imitation task performance and whether the patterns of association varied across the different ages. Language ability emerged as a predictor of immediate Elicited Imitation performance by 24 months of age and predicted delayed performance at each age. In addition to the contributions of language, children's abilities to search for and retrieve toys in the deliberate memory task were associated with their immediate Elicited Imitation performance at each age. In addition to language, working memory was positively associated with aspects of both immediate and delayed performance at all ages. The extent to which it was possible to replicate and extend previous cross-sectional work in this longitudinal study is discussed.

Life-span development of visual working memory: when is feature binding difficult?

We asked whether the ability to keep in working memory the binding between a visual object and its spatial location changes with development across the life span more than memory for item information. Paired arrays of colored squares were identical or differed in the color of one square, and in the latter case, the changed color was unique on that trial (item change) or was duplicated elsewhere in the array (color-location binding change). Children (8-10 and 11-12 years old) and older adults (65-85 years old) showed deficits relative to young adults. These were only partly simulated by dividing attention in young adults. The older adults had an additional deficiency, specifically in binding information, which was evident only when item- and binding-change trials were mixed together. In that situation, the older adults often overlooked the more subtle, binding-type changes. Some working memory processes related to binding undergo life-span development in an inverted-U shape, whereas other, bias- and salience-related processes that influence the use of binding information seem to develop monotonically.

Word and face recognition in children with congenital hypothyroidism: an event-related potential study

The repetition paradigm offers a useful technique for assessing recognition memory by evaluating how an individual responds to new versus old stimuli. While this paradigm has been extensively used in adults with and without clinical conditions, it has not, to our knowledge, been studied in a clinical pediatric population. Children with congenital hypothyroidism (CH) identified by newborn screening and treated early in life have normal intelligence but demonstrate residual cognitive deficits including selective memory problems that are attributed to their loss of thyroid hormone during hippocampal formation. Since the hippocampus is integral for recognition memory, we hypothesized that children with CH would perform atypically on the repetition paradigm. Event-related potentials (ERPs) were recorded during word and face recognition in nine children aged 11 to 13 years with CH and nine typically developing children matched for age. Results revealed that while the groups did not differ in accuracy or reaction time, they did differ significantly on selective ERP components. Like normal adults, the comparison children showed a positive elevation in P3 amplitude for repeated relative to new words at the parietal electrodes, whereas children with CH did not. Both groups produced weak repetition effects when viewing faces, although the amplitudes of children with CH were somewhat smaller. It is proposed that the dampened neurophysiological response to repeated verbal stimuli by children with CH may explain some of their clinically observed difficulties in short-term recognition memory.

Evidence of Developmental Differences in Implicit Sequence Learning: An fMRI Study of Children and Adults

Prevailing theories of implicit or unaware learning propose a developmental invariance model, with implicit function maturing early in infancy or childhood despite prolonged improvements in explicit or intentional learning and memory systems across childhood. Neuroimaging studies of adult visuomotor sequence learning have associated fronto-striatal brain regions with implicit learning of spatial sequences. Given evidence of continued development in these brain regions during childhood, we compare implicit sequence learning in adults and 7- to 11-year-old children to examine potential developmental differences in the recruitment of fronto-striatal circuitry during implicit learning. Participants performed a standard serial reaction time task. Stimuli alternately followed a fixed 10-step sequence of locations or were presented in a pseudorandom order of locations. Adults outperformed children, achieving a significantly larger sequence learning effect and showing learning more quickly than children. Age-related differences in activity were observed in the premotor cortex, putamen, hippocampus, inferotemporal cortex, and parietal cortex. We observed differential recruitment of cortical and subcortical motor systems between groups, presumably reflecting age differences in motor response execution. Adults showed greater hippocampal activity for sequence trials, whereas children demonstrated greater signal during random trials. Activity in the right caudate correlated significantly with behavioral measures of implicit learning for both age groups, although adults showed greater signal change than children overall, as would be expected given developmental differences in sequence learning magnitude. These results challenge the idea of developmental invariance in implicit learning and instead support a view of parallel developments in implicit and explicit learning systems.