Developmental changes in the specificity of memory over the first year of life

The Development of Flexible Problem Solving: An Integrative Approach

Flexible problem solving, the ability to deal with currently goal-irrelevant information that may have been goal-relevant in previous, similar situations, plays a prominent role in cognitive development and has been repeatedly investigated in developmental research. However, this research, spanning from infancy to the school years, lacks a unifying framework, obscuring the developmental timing of flexible problem solving. Therefore, in this review paper, previous findings are gathered, organized, and integrated under a common framework to unveil how and when flexible problem solving develops. It is showed that the development of flexible problem solving coincides with increases in executive functions, that is, inhibition, working memory and task switching. The analysis of previous findings shows that dealing with goal-irrelevant, non-salient information received far more attention than generalizing in the presence of goal-irrelevant, salient information. The developmental timing of the latter can only be inferred from few transfer studies, as well as executive functions, planning and theory of mind research, to highlight gaps in knowledge and sketch out future research directions. Understanding how transfer in the presence of seemingly relevant but truly irrelevant information develops has implications for well-balanced participation in information societies, early and lifespan education, and investigating the evolutionary trajectory of flexible problem solving.

Memory for nonadjacent dependencies in the first year of life and its relation to sleep

Grammar learning requires memory for dependencies between nonadjacent elements in speech. Immediate learning of nonadjacent dependencies has been observed in very young infants, but their memory of such dependencies has remained unexplored. Here we used event-related potentials to investigate whether 6- to 8-month-olds retain nonadjacent dependencies and if sleep after learning affects this memory. Infants were familiarised with two rule-based morphosyntactic dependencies, presented in sentences of an unknown language. Brain responses after a retention period reveal memory of the nonadjacent dependencies, independent of whether infants napped or stayed awake. Napping, however, altered a specific processing stage, suggesting that memory evolves during sleep. Infants with high left frontal spindle activity show an additional brain response indicating memory of individual speech phrases. Results imply that infants as young as 6 months are equipped with memory mechanisms relevant to grammar learning. They also suggest that during sleep, consolidation of highly specific information can co-occur with changes in the nature of generalised memory.

Sensorimotor Contingencies as a Key Drive of Development: From Babies to Robots

Much current work in robotics focuses on the development of robots capable of autonomous unsupervised learning. An essential prerequisite for such learning to be possible is that the agent should be sensitive to the link between its actions and the consequences of its actions, called sensorimotor contingencies. This sensitivity, and more particularly its role as a key drive of development, has been widely studied by developmental psychologists. However, the results of these studies may not necessarily be accessible or intelligible to roboticians. In this paper, we review the main experimental data demonstrating the role of sensitivity to sensorimotor contingencies in infants' acquisition of four fundamental motor and cognitive abilities: body knowledge, memory, generalization, and goal-directedness. We relate this data from developmental psychology to work in robotics, highlighting the links between these two domains of research. In the last part of the article we present a blueprint architecture demonstrating how exploitation of sensitivity to sensorimotor contingencies, combined with the notion of "goal," allows an agent to develop new sensorimotor skills. This architecture can be used to guide the design of specific computational models, and also to possibly envisage new empirical experiments.

The ontogeny of memory persistence and specificity

Interest in the ontogeny of memory blossomed in the twentieth century following the initial observations that memories from infancy and early childhood are rapidly forgotten. The intense exploration of infantile amnesia in subsequent years has led to a thorough characterization of its psychological determinants, although the neurobiology of memory persistence has long remained elusive. By contrast, other phenomena in the ontogeny of memory like infantile generalization have received relatively less attention. Despite strong evidence for reduced memory specificity during ontogeny, infantile generalization is poorly understood from psychological and neurobiological perspectives. In this review, we examine the ontogeny of memory persistence and specificity in humans and nonhuman animals at the levels of behavior and the brain. To this end, we first describe the behavioral phenotypes associated with each phenomenon. Looking into the brain, we then discuss neurobiological mechanisms in the hippocampus that contribute to the ontogeny of memory. Hippocampal neurogenesis and critical period mechanisms have recently been discovered to underlie amnesia during early development, and at the same time, we speculate that similar processes may contribute to the early bias towards memory generalization.

Ontogenesis of learning and memory: Biopsychosocial and dynamical systems perspectives

In this article, we review recent empirical and theoretical work on infant memory development, highlighting future directions for the field. We consider the state of the field since Carolyn Rovee-Collier's call for developmental scientists to "shift the focus from what to why," emphasizing the function of infant behavior and the value of integrating fractionized, highly specialized subfields. We discuss functional approaches of early learning and memory, including ecological models of memory development and relevant empirical work in human and non-human organisms. Ontogenetic changes in learning and memory occur in developing biological systems, which are embedded in broader socio-cultural contexts with shifting ecological demands that are in part determined by the infants themselves. We incorporate biopsychosocial and dynamical systems perspectives as we analyze the state of the field's integration of multiple areas of specialization to provide more holistic understanding of the contributing factors and underlying mechanisms of the development of memory.

Effects of context variability on 2-year-olds' fact and word learning

The current study investigated the effects of context variability on 2.5-year-olds' (N = 48) fact and word learning. Children were taught labels or facts for novel objects that were presented on variable or consistent background contexts during training. At test, children were asked to select target items in a context that either matched training contexts or was entirely new. Children learned words at above-chance levels regardless of context variability, and there was no significant difference in learning between children in variable and consistent training conditions. For facts, on the other hand, children demonstrated above-chance target selection only when contexts matched between training and test. In addition, children's immediate target selection was lower in the variable context condition than in the consistent one. However, this difference was not present after a 10-min delay. Results are discussed in terms of why fact learning and word learning may be differentially affected by context variability.

How self-generated labelling shapes transfer of learning during early childhood: The role of individual differences

Multiple factors influence imitation during toddlerhood, including task complexity, social contingency, and individual differences. We conducted a secondary data analysis of individual differences in self-generated labelling using data collected from a complex puzzle imitation task with 355 2- to 3-year-olds. This analysis indicated that toddlers' ability to label the completed puzzle (fish or boat) was associated with better imitation performance. Labelling occurs during social interactions; therefore, our second analysis tested how labelling differed as a function of the level of social scaffolding in each condition. This analysis revealed that self-generated labelling was lower when the social demonstrator was removed and the task was presented on a touchscreen. This study is one of the first to examine self-generated labelling during a complex imitation task in toddlers and increases our understanding of the complexity of memory processing needed for imitation learning. Statement of contribution What is already known on this subject? Toddlers exhibit a transfer of learning deficit from 2D media, including books, TV, and tablets. Self-generated labelling enhances children's learning, through attentional and cognitive mechanisms. Children are sensitive to reduced social cues in screen media contributing to the transfer deficit. What does this study add? Self-generated labelling is associated with better goal imitation performance. Self-generated labelling occurs more frequently under social conditions.

2.5-year-olds' retention and generalization of novel words across short and long delays

Two experiments investigated two-year-olds' retention and generalization of novel words across short and long time delays. Specifically, retention of newly learned words and generalization to novel exemplars or novel contexts were tested one minute or one week after learning. Experiment 1 revealed successful retention as well as successful generalization to both new exemplars and new contexts after a one-minute delay, with no statistical differences between retention and generalization performance for either generalization type. Toddlers tested after a week delay (Experiment 2) showed successful retention and generalization as well, but while context generalization was statistically equivalent to retention accuracy, exemplar generalization was significantly lower than retention accuracy. The overall success in both retention and generalization suggests that toddlers' newly learned words are robust and flexible. However, the lower exemplar generalization performance compared to retention after a weeklong delay suggests that novel words may become less flexible across exemplar characteristics over time.

Naps promote flexible memory retrieval in 12-month-old infants

Flexibility in applying existing knowledge to similar cues is a corner stone of memory development in infants. Here, we examine the effect of sleep on the flexibility of memory retrieval using a deferred imitation paradigm. Forty-eight 12-month-old infants were randomly assigned to either a nap or a no-nap demonstration condition (scheduled around their natural daytime sleep schedule) or to a baseline control condition. In the demonstration conditions, infants watched an experimenter perform three target actions on a hand puppet. Immediately afterwards, infants were allowed to practice the target actions three times. In a test session 4-hr later, infants were given the opportunity to reproduce the actions with a novel hand puppet differing in color from the puppet used during the demonstration session. Only infants in the nap-condition performed significantly more target actions than infants in the baseline control condition. Furthermore, they were faster to carry out the first target action than infants in the no-nap condition. We conclude that sleep had a facilitative effect on infants' flexibility of memory retrieval.

Category generalization in a new context: the role of visual attention

Infants and children have difficulty categorizing objects in new contexts. However, learning in both same and varied contexts can help young word learners overcome contextual learning difficulties. We examined the relation between infants' visual attention to the category member and background context during learning and their ability to generalize a new category member in a new context. Of particular interest is how this relation is affected by learning in various contextual conditions. Infants (16-20 months; n=48) were presented with eight novel noun categories in one of three contextual conditions (same context, varied context, or a combination of same and varied contexts), and tested for their generalization ability in a new context. Context was defined as the colored and patterned fabric upon which the object was presented. Results suggest that visual attention during learning is associated with category generalization ability in a new context only for infants whose learning took place in a combination of same and varied background contexts. The results are discussed in terms of the mechanisms by which context affects generalization.

Development of adaptive tool-use in early childhood: sensorimotor, social, and conceptual factors

Tool-use is specialized in humans, and juvenile humans show much more prolific and prodigious tool-use than other juvenile primates. Nonhuman primates possess many of the basic motor and behavioral capacities needed for manual tool-use: perceptual-motor specialization, sociocultural practices and interactions, and abstract conceptualization of kinds of functions, both real and imagined. These traits jointly contribute to the human specialization for tool-using. In particular, from 2 to 5 years of age children develop: (i) more refined motor routines for interacting with a variety of objects, (ii) a deeper understanding and awareness of the cultural context of object-use practices, and (iii) a cognitive facility to represent potential dynamic human-object interactions. The last trait, which has received little attention in recent years, is defined as the ability to form abstract (i.e., generalizable to novel contexts) representations of kinds of functions, even with relatively little training or instruction. This trait might depend not only on extensive tool-using experience but also on developing cognitive abilities, including a variety of cognitive flexibility: specifically, imagistic memory for event sequences incorporating causal inferences about mechanical effects. Final speculations point to a possible network of neural systems that might contribute to the cognitive capacity that includes sensorimotor, sensory integration, and prefrontal cortical resources and interconnections.

When do infants begin recognizing familiar words in sentences?

Previous studies have shown that by 11 but not by 10 months infants recognize words that have become familiar from everyday life independently of the experimental setting. This study explored the ability of 10-, 11-, and 12-month-old infants to recognize familiar words in sentential context, without experimental training. The headturn preference procedure was used to contrast passages containing words likely to be familiar to the infants with passages containing words unlikely to have been previously heard. Two stimulus words were inserted near the beginning and end of each of a set of simple sentence frames. The ability to recognize the familiar words within sentences emerged only at 12 months of age. The contrast between segmentation abilities as they emerge as a result of everyday exposure to language, as assessed here, and those abilities as measured in studies in which words are experimentally trained is discussed in terms of memory-based mechanisms.

Four-month-old infants' long-term memory for a stressful social event

Infants clearly show an early capacity for memory for inanimate emotionally neutral events. However, their memory for social stress events has received far less attention. The aim of the study was to investigate infants' memory for a stressful social event (i.e., maternal unresponsiveness during the Still-Face paradigm) after a 15-day recall interval using changes in behavioral responses and salivary post-stress cortisol reactivity as measures of memory. Thirty-seven infants were exposed to social stress two times (experimental condition); the first time when they were 4 months of age and second exposure after a 2 week interval. Infants in the control condition (N = 37) were exposed to social stress just one time, at the age corresponding to the second exposure for infants in the experimental condition (4 months plus 2 weeks). Given individual differences in infants' reactivity to social stress events, we categorized infants as increasers or decreasers based on their cortisol reactivity after their initial exposure to the stress of the maternal still-face. Infants in the experimental condition, both increasers and decreasers, showed a significant change in cortisol response after the second exposure to the maternal still-face, though change was different for each reactivity group. In contrast, age-matched infants with no prior exposure to the maternal still-face showed similar post-stress cortisol reactivity to the reactivity of the experimental infants at their first exposure. There were no behavioral differences between increasers and decreasers during the Still-Face paradigm and exposures to the social stress. Thus differences between the experimental and control groups' post-stress cortisol reactivity was associated with the experimental group having previous experience with the social stress. These findings indicate long-term memory for social stress in infants as young as 4 months of age.

Highchair philosophers: the impact of seating context-dependent exploration on children's naming biases

We examine developmental interactions between context, exploration, and word learning. Infants show an understanding of how nonsolid substances are categorized that does not reliably transfer to learning how these categories are named in laboratory tasks. We argue that what infants learn about naming nonsolid substances is contextually bound - most nonsolids that toddlers are familiar with are foods and thus, typically experienced when sitting in a highchair. We asked whether 16-month-old children's naming of nonsolids would improve if they were tested in that typical context. Children tested in the highchair demonstrated better understanding of how nonsolids are named. Furthermore, context-based differences in exploration drove differences in the properties attended to in real-time. We discuss what implications this context-dependency has for understanding the development of an ontological distinction between solids and nonsolids. Together, these results demonstrate a developmental cascade between context, exploration, and word learning.

Who is she? Changes in the person context affect categorization

Changes between the learning and testing contexts affect learning, memory, and generalization. We examined whether a change (between learning and testing) in the person children were interacting with affects generalization. Three-, four-, and five-year-old children were trained on eight novel noun categories by one experimenter. Children were tested for their ability to generalize the label to a new category member by either the same experimenter who trained them or by a novel experimenter. Three-year-old children's performance was not affected by who they were tested by. Four- and five-year-old children's performance was lower when tested by the novel experimenter. The results are discussed in terms of source monitoring and the effect of perceptual context change on category generalization.

Same, varied, or both? Contextual support aids young children in generalizing category labels

Children have a difficult time in generalizing among changes in background context. We examined the role of two processes that may aid in generalizing category labels in new contexts. In this study, 2-year-old children were taught novel object categories in one type of contextual condition and were tested for category generalization in a new context. In Experiment 1, children (N=48) learned in one of three conditions: (a) all category instances presented in the same context, (b) all category instances presented in varied contexts, or (c) some category instances presented in the same context and some presented in varied contexts. In Experiment 2, children (N=48) learned in one of three conditions, all of which included presentations in the same context and varied contexts but differed in order. Results from both experiments revealed that children were significantly more likely to choose the correct object when training was in both same and varied contexts regardless of order. The results suggest that contextual factors, by providing both support for aggregation and support for decontextualization, contribute to word learning and generalization for novice word learners.

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.

Odor as a contextual cue in memory reactivation in young infants

Three-month-old infants were trained to move a mobile in the presence of a coconut or cherry odor (context). Six days later, a reactivation session took place. Infants were randomly assigned to 4 groups (same odor during training and reactivation, different odor during training and reactivation, no odor present during reactivation, no reactivation). A retention test was conducted 24h later in the presence of the training odor and mobile. Retention was seen only in the group of infants trained and reactivated with the same odor. This indicates that olfactory contextual cues function in a similar manner to visual and auditory contextual cues in that a novel context, or the absence of the context in which the memory was formed, are ineffective as reminders once the original memory has been forgotten.

Early operant learning is unaffected by socio-economic status and other demographic factors: a meta-analysis

The relation between SES (socioeconomic status) and academic achievement in school-aged children is well established; children from low SES families have more difficulty in school. However, few studies have been able to establish a link between SES and learning in infancy, and thus the developmental onset of SES effects remains unknown. The limited studies that have been conducted to explore the link between SES and learning in infancy have generated mixed results; some demonstrate a link between SES and learning in infants as young as 6-9 months (Smith, Fagan, & Ulvund, 2002) while others do not. Further, studies examining the genetic as well as environmental contributors to learning in infancy and early childhood suggest that the effect of SES is likely cumulative and that as children develop, the effect of a low SES environment will become more pronounced (Tucker-Drob, Rhemtulla, Harden, Turkheimer, & Fask, 2011). Using aggregated data from 790 infants collected across 18 studies, we examined the contribution of SES and other demographic factors to learning of an operant kicking task in 2-4-month-old infants in a meta-analysis. Results indicated that, at least with respect to operant conditioning, an infant is an infant; that is SES did not affect learning rate or ability to learn in infants under 4-months of age. SES effects may therefore be better characterized as cumulative, with tangible effects emerging sometime later in life.

Fast Mapping Across Time: Memory Processes Support Children's Retention of Learned Words

Children's remarkable ability to map linguistic labels to referents in the world is commonly called fast mapping. The current study examined children's (N = 216) and adults' (N = 54) retention of fast-mapped words over time (immediately, after a 1-week delay, and after a 1-month delay). The fast mapping literature often characterizes children's retention of words as consistently high across timescales. However, the current study demonstrates that learners forget word mappings at a rapid rate. Moreover, these patterns of forgetting parallel forgetting functions of domain-general memory processes. Memory processes are critical to children's word learning and the role of one such process, forgetting, is discussed in detail - forgetting supports extended mapping by promoting the memory and generalization of words and categories.

Redundant amodal properties facilitate operant learning in 3-month-old infants

The current study examined the role redundant amodal properties play in an operant learning task in 3-month-old human infants. Prior studies have suggested that the presence of redundant amodal information facilitates detection and discrimination of amodal properties and potentially functions to influence general learning processes such as associative conditioning. The current study examined how human infants use redundant amodal information (visual and haptic) about the shape of an object to influence learning of an operant response. Infants learned to kick to move a mobile of cylinders while either holding a cylinder, a rectangular cube, or no object. Kick rate served as the dependent measure. The results showed that infants given matching redundant amodal properties (e.g., viewed cylinders while holding a cylinder) showed facilitated operant learning whereas infants given mismatching redundant amodal properties showed inhibited operant learning. These results support and extend the Intersensory Redundancy Hypothesis by demonstrating that amodal redundancy influences complex learning processes such as operant conditioning.

Long-term transfer of learning from books and video during toddlerhood

Television viewing and picture book reading are prevalent activities during toddlerhood, and research has shown that toddlers can imitate from both books and videos after short delays. This is the first study to directly compare toddlers' long-term retention rates for target actions learned from a video or book. Toddlers (N=158) at 18- and 24-months of age saw an experimenter demonstrating how to make a novel three-step toy rattle via a prerecorded video or a picture book. The toddlers' imitation of the target actions was tested after a specific delay (e.g., 2, 4 weeks), and their performance was compared with that of age-matched controls who did not see a demonstration. The 18-month-olds retained the target actions for 2 weeks, exhibiting forgetting at 4 weeks, whereas the 24-month-olds retained the information for up to 4 weeks, exhibiting forgetting at 8 weeks. Retention rates for books and videos did not differ at either age. These findings demonstrate very impressive retention from a brief two-dimensional media demonstration, and they contribute to our overall understanding of long-term memory processes during infancy.

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.

Potentiation in young infants: the origin of the prior knowledge effect?

In two experiments with 6-month-old infants, we found that prior learning of an operant task (remembered for 2 weeks) mediated new learning of a modeling event (remembered for only 1 day) and increased its recall. Infants first learned to associate lever pressing with moving a toy train housed in a large box. One or 2 weeks later, three target actions were modeled on a hand puppet while the train box (a retrieval cue) was in view. Merely retrieving the train memory strengthened it, and simultaneously pairing its retrieved memory with the modeled actions potentiated their learning and recall. When paired 1 week later, deferred imitation increased from 1 day to 4 weeks; when paired 2 weeks later, it increased from 1 day to 6 weeks. The striking parallels between potentiated learning in infants and the prior knowledge effect in adults suggests that the prior knowledge effect originates in early infancy.

Time windows in retention over the first year-and-a-half of life: spacing effects

The time window construct describes when and how an earlier experience will be enduring. According to the construct, there is a limited period after an event occurs, or time window, in which a second event can retrieve and be integrated with the memory of the first event. The construct also holds that when the integration occurs later in the time window, its effects are more enduring. This study examined the time window construct for session spacing with 6- to 18-month-old human infants. Infants of all ages exhibited the retention benefit of two (integrated) sessions only when the second session occurred within the time window, but only 6-month-olds remembered longer when it occurred late in the time window. Combined with 3-month-olds' data, these findings document the generality and predictive validity of the time window construct throughout the infancy period with one modification: Integration late in the time window only benefits infants younger than 9 months.

Developmental differences in children's context-dependent word learning

In this study, 2.5-, 3-, and 4-year-olds (N=108) participated in a novel noun generalization task in which background context was manipulated. During the learning phase of each trial, children were presented with exemplars in one or multiple background contexts. At the test, children were asked to generalize to a novel exemplar in either the same or a different context. The 2.5-year-olds' performance was supported by matching contexts; otherwise, children in this age group demonstrated context dependent generalization. The 3-year-olds' performance was also supported by matching contexts; however, children in this age group were aided by training in multiple contexts as well. Finally, the 4-year-olds demonstrated high performance in all conditions. The results are discussed in terms of the relationship between word learning and memory processes; both general memory development and memory developments specific to word learning (e.g., retention of linguistic labels) are likely to support word learning and generalization.

Age-related changes in visual recognition memory during infancy and early childhood

Age-related changes in long-term memory during infancy and early childhood were examined using the Visual Recognition Memory (VRM) procedure. Independent groups of 1-, 2-, 3-, and 4-year-olds were familiarized with a visual stimulus and were tested either immediately or after a delay that ranged from 24 hr to 6 months. Although all age groups exhibited a significant novelty preference when tested immediately after familiarization, clear age-related differences emerged over longer retention intervals. We conclude that age-related increases in basic retention are a fundamental aspect of mammalian memory development and, in humans, these increases may play a vital role in the offset of childhood amnesia.

Transfer of learning between 2D and 3D sources during infancy: Informing theory and practice

The ability to transfer learning across contexts is an adaptive skill that develops rapidly during early childhood. Learning from television is a specific instance of transfer of learning between a 2-Dimensional (2D) representation and a 3-Dimensional (3D) object. Understanding the conditions under which young children might accomplish this particular kind of transfer is important because by 2 years of age 90% of US children are viewing television on a daily basis. Recent research shows that children can imitate actions presented on television using the corresponding real-world objects, but this same research also shows that children learn less from television than they do from live demonstrations until they are at least 3 years old; termed the video deficit effect. At present, there is no coherent theory to account for the video deficit effect; how learning is disrupted by this change in context is poorly understood. The aims of the present review are (1) to review the conditions under which children transfer learning between 2D images and 3D objects during early childhood, and (2) to integrate developmental theories of memory processing into the transfer of learning from media literature using Hayne's (2004) developmental representational flexibility account. The review will conclude that studies on the transfer of learning between 2D and 3D sources have important theoretical implications for general developmental theories of cognitive development, and in particular the development of a flexible representational system, as well as policy implications for early education regarding the potential use and limitations of media as effective teaching tools during early childhood.

Children's autobiographical reports about sexual abuse: A narrative review of the research literature

BACKGROUND

The empirical and theoretical literature on children's autobiographical statements about child sexual abuse and other forms of maltreatment should be of potential importance to all professionals who regularly interview children as part of their professional duties.

AIMS

To present an introduction to this field.

METHODS

Narrative review.

RESULTS

Preschool children appear to be capable of providing reliable testimony on highly salient personal experiences such as sexual abuse, though a substantial proportion of children may choose not to. However, suggestive interviewing practises, particularly when used with younger children, may elicit false allegations. There is little evidence to suggest that experiences from the preverbal period of life can later be meaningfully reconstructed by means of statements or clinical signs.

CONCLUSIONS

Use of children as witnesses and informants requires special considerations, knowledge and skills.

Flexibility in infant actions during arm- and leg-based learning in a mobile paradigm

To understand young infants' flexible changes of learned actions when abrupt environmental changes occur, we examined fifty-four 3-month-olds who performed a mobile task, in which they learned to move the mobile by a string attached to their arms or legs (arm-based or leg-based learning). We manipulated the order of tests-arm to leg (AL) and leg to arm (LA)-and observed the time course of motion of four limbs. The infants in the AL condition showed a differentiated movement pattern, in which the movement of the connected arm was dominant, and when the connected limb changed, they immediately inhibited the prior movement pattern. The infants in the LA condition produced undifferentiated movement pattern of multiple limbs, which was maintained even when the critical limb was changed. The results suggest that the infants' flexibility of actions in a novel situation depends on the prior experience. We speculate neural mechanisms, which may underlie the difference between the arm-based and leg-based learning.

Simplicity and generalization: Short-cutting abstraction in children's object categorizations

Development in any domain is often characterized by increasingly abstract representations. Recent evidence in the domain of shape recognition provides one example; between 18 and 24 months children appear to build increasingly abstract representations of object shape [Smith, L. B. (2003). Learning to recognize objects. Psychological Science, 14, 244-250]. Abstraction is in part simplification because it requires the removal of irrelevant information. At the same time, part of generalization is ignoring irrelevant differences. The resulting prediction is this: simplification may enable generalization. Four experiments asked whether simple training instances could shortcut the process of abstraction and directly promote appropriate generalization. Toddlers were taught novel object categories with either simple or complex training exemplars. We found that children who learned with simple objects were able to generalize according to shape similarity, typically relevant for early object categories, better than those who learned with complex objects. Abstraction is the product of learning; using simplified - already abstracted instances - can short-cut that learning, leading to robust generalization.

The specificity of priming effects over the first year of life

Despite its significance for the enduring effect of early experience, the specificity of priming on infants' forgotten memories is unknown. This study determined the impact of cue and context changes on the initial priming and retrieval of the reactivated memory over the first postnatal year. Infants were operantly trained with a distinctive cue in a particular context. After forgetting, they were primed and tested for renewed retention with combinations of old and new cues and contexts. Priming was hyperspecific to the original cue and original context at all but 12 months, when the memory was reactivated in a novel context. At 9-12 months, the reactivated memory generalized to a novel cue or context. At younger ages, the reactivated memory generalized only after a very brief prime. These findings indicate that priming in early infancy is initially conservative, buffering against recovering memories in contexts that might no longer be appropriate.

Crawling is associated with more flexible memory retrieval by 9-month-old infants

In the present experiment, we used a deferred imitation paradigm to explore the effect of crawling on memory retrieval by 9-month-old human infants. Infants observed an experimenter demonstrate a single target action with a novel object and their ability to reproduce that action was assessed after a 24-hr delay. Some infants were tested with the demonstration stimulus in the demonstration context and some infants were tested with a different stimulus in a different context. Half of the infants in each test condition were crawling at the time of participation and half were not. Both crawling and non-crawling infants exhibited retention when tested with the demonstration stimulus in the demonstration context, but only infants who were crawling by 9 months of age exhibited retention when tested with a different stimulus in a different context. These findings demonstrate that the onset of independent locomotion is associated with more flexible memory retrieval during the first year of life.

Fast tracking: infants learn rapidly about object trajectories

Research on early object concept formation has the potential to provide a unique contribution to the debate between constructivism and nativism but has, thus far, generated only controversy. New research by Kochukhova and Gredebäck that examined infants' predictions of the reappearance of an occluded object offers new insight into not only when but how such concepts are acquired.

Learning about occlusion: initial assumptions and rapid adjustments

We examined 6-month-olds abilities to represent occluded objects, using a corneal-reflection eye-tracking technique. Experiment 1 compared infants' ability to extrapolate the current pre-occlusion trajectory with their ability to base predictions on recent experiences of novel object motions. In the first condition infants performed at asymptote ( approximately 2/3 accurate predictions) from the first occlusion passage. In the second condition all infants initially failed to make accurate prediction. Performance, however, reached asymptote after two occlusion passages. This is the first study that demonstrates such rapid learning effects during an occlusion task. Experiment 2 replicates these effects and demonstrates a robust memory effect extending 24h. In occlusion tasks such long-term memory effects have previously only been observed in 14-month-olds (Moore & Meltzoff, 2004).

General to specific development of movement patterns and memory for contingency between actions and events in young infants

To understand infants' learning of the contingency between their actions and events, we studied inter-limb movement patterns of 48 infants aged 2-4 months when they attempted moving a mobile using a string attached to their arm. The session was composed of baseline, acquisition, immediate retention test, re-acquisition, interference, and delayed retention test periods. The analysis revealed motor pattern dependence on age--infants exhibited increased movement over base line of all limbs (2-month-olds), both arms (3-month-olds), and the connected arm (4-month-olds). The acquired patterns were produced during immediate and delayed test periods across age groups. The results suggest that 2-month-olds can acquire and retain general body movements that induce contingent changes in a mobile, while 3- and 4-month-olds form memories that serve as a constraint enabling highly specific movement of their arm to effectively activate the mobile.

Effects of priming duration on retention over the first 1 1/2 years of life

Exposing individuals to an isolated component (a prime) of a prior event alleviates its forgetting. Two experiments with 120 human infants between 3 and 18 months of age determined the minimum duration of a prime that can reactivate a forgotten memory and how long the reactivated memory persists. Infants learned an operant task, forgot it, were exposed to the prime, and later were tested for renewed retention. In Experiment 1, the minimum duration of an effective prime decreased logarithmically with age, but was always longer than the duration of a mere glance. In Experiment 2, the reactivated memory was forgotten twice as fast after a minimum-duration prime as after a full-length one, irrespective of priming delay and infant age. These data reveal that the minimum effective prime duration psychophysically equates the accessibility of forgotten memories. We conclude that priming is perceptually based with effects that are organized on a ratio (log) scale.

Retrieval Protracts Deferred Imitation by 6-Month-Olds

Past research using a deferred imitation task has shown that 6-month-olds remember a 3-part action sequence for only 1 day. The concept of a time window suggests that there is a limited period within which additional information can be integrated with a prior memory. Its width tracks the forgetting function of the memory. This study asked if retrieving the memory of the modeled actions at the end of the time window protracts its retention, if the type of retrieval (active or passive) differentially influences retention, and if the retrieval delay influences its specificity. In Experiment 1, 6-month-olds either imitated the modeled actions (active retrieval group) or merely watched them modeled again (passive retrieval group) 1 day after the original demonstration. Both groups showed deferred imitation after 10 days. In Experiment 2, 6-month-olds who repeatedly retrieved the memory at or near the end of the time window deferred imitation for 2.5 months. In Experiment 3,6-month-olds spontaneously generalized imitation late in the time window after 1 prior retrieval, whether it was active or passive. These studies reveal that the retention benefit of multiple retrievals late in the time window is huge. Because most retrievals are undoubtedly latent, the contribution of repeated events to the growth of the knowledge base early in infancy has been greatly underestimated.

The social context of imitation in infancy

Infants increasingly generalize deferred imitation across environmental contexts between 6 and 18 months of age. In three experiments with 126 6-, 9-, 12-, 15-, and 18-month-olds, we examined the role of the social context in deferred imitation. One experimenter demonstrated target actions on a hand puppet, and a second experimenter tested imitation 24h later. When the second experimenter was novel, infants did not exhibit deferred imitation at any age; when infants were preexposed to the second experimenter, all of them did. Imitating immediately after the demonstration also facilitated deferred imitation in a novel social context at all ages but 6 months. Infants' pervasive failure to exhibit deferred imitation in a novel social context may reflect evolutionary selection pressures that favored conservative behavior in social animals.

Updating reactivated memories in infancy: I. Passive- and active-exposure effects

This study examined the vulnerability of infants' reactivated memories to modification. In three experiments, one hundred eight 3-month-olds learned to move a distinctive mobile by kicking. After the operant task was forgotten, its memory was recovered by a reactivation treatment. Immediately afterward, attempts were made to modify the reactivated memory by exposing infants to a novel mobile. Exposing the novel mobile immediately after the reactivation treatment did not affect the reactivated memory (Experiment 1). When exposure to the novel mobile was delayed for 24 hr, the novel mobile temporarily interfered with recognition of the original mobile, but did not modify the reactivated memory (Experiment 2). Only when the contingency was briefly associated with the novel mobile (an active-exposure procedure) was the reactivated memory modified (Experiment 3). These data reveal that infants' recently reactivated memories are surprisingly resistant to updating unless the operant contingency that established the original memory accompanies the new information.

Generalization of deferred imitation during the first year of life

Infants first generalize across contexts and cues at 3 months of age in operant tasks but not until 12 months of age in imitation tasks. Three experiments using an imitation task examined whether infants younger than 12 months of age might generalize imitation if conditions were more like those in operant studies. Infants sat on a distinctive mat in a room in their home (the context) while an adult modeled actions on a hand puppet (the cue). When they were tested 24 h later, 6-month-olds generalized imitation when either the mat or the room (but not both) differed, whereas 9-month-olds generalized when both the mat and the room differed. In addition, 9-month-olds who imitated immediately also generalized to a novel test cue, whereas 6-month-olds did not. These results parallel results from operant studies and reveal that the similarity between the conditions of encoding and retrieval-not the type of task-determines whether infants generalize. The findings offer further evidence that memory development during infancy is a continuous function.

Object permanence after a 24-hr delay and leaving the locale of disappearance: the role of memory, space, and identity

Fourteen-month-old infants saw an object hidden inside a container and were removed from the disappearance locale for 24 hr. Upon their return, they searched correctly for the hidden object, demonstrating object permanence and long-term memory. Control infants who saw no disappearance did not search. In Experiment 2, infants returned to see the container either in the same or a different room. Performance by room-change infants dropped to baseline levels, suggesting that infant search for hidden objects is guided by numerical identity. Infants seek the individual object that disappeared, which exists in its original location, not in a different room. A new behavior, identity-verifying search, was discovered and quantified. Implications are drawn for memory, spatial understanding, object permanence, and object identity.