Verbal cues facilitate memory retrieval during infancy

In three experiments, 18-month-olds were tested in a deferred imitation paradigm. Some infants received verbal information during the demonstration and at the time of the test (full narration), and some did not (empty narration). When tested after a 4-week delay, infants given full narration exhibited superior retention relative to infants given empty narration (Experiment 1). This retention advantage appears to be due to the effects of verbal cues at the time of memory retrieval. There was no effect of verbal cues that were presented only at the time of original encoding (Experiment 2A). Furthermore, infants who received verbal cues only at the time of retrieval exhibited superior retention relative to infants who received verbal cues only at the time of original encoding (Experiment 2B). These findings demonstrate that verbal cues can enhance memory retrieval by participants who are not yet fluent speakers themselves.     

Olfactory context and memory retrieval in 3-month-old infants

Three experiments examineed whether olfactory stimuli can produce context-dependent effects in infant memory. In eash, 3-month-old infants learned to kick to control the movement of an overhead modile in the presence of an ambient odor. Retention was assessed 1, 3, or 5 days later. During the retention test, the olfactory context was either the same odor, a different odor, or “no odor.” At 1 day, infants exhibited retention when tested in the presence of the same odor. Infants in the no odor condition exhibited partial retention, whereas memory retrieval was completely disrupted for infants tested in the presence of the different odor. After the 3- and 5-day intervals, all groups showed forgetting. These results were not consistent with recent studies of 3-month-old infants trained and tested in the presence of a distinctive visual and auditory context. The findings suggest that olfactory stimuli are a silent feature of the environment for 3-month-old infants, but that they function as context cues in a way that differs from other sensory modalities.     

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.     

A systemically administered beta-adrenoceptor antagonist blocks corticosterone-induced impairment of contextual memory retrieval in rats

Several studies have reported that glucocorticoids impair memory retrieval. The present study examined in male Sprague-Dawley rats the effects of systemically administered corticosterone on retrieval of memory for inhibitory avoidance training. Corticosterone (3.0mg/kg, s.c.) injected 30min before retention testing, 48h after training, significantly impaired retention performance, as compared to vehicle treatment, of rats tested in the training context. In contrast, corticosterone administration did not impair retrieval when rats were tested for retention in a different context. Corticosterone did also not impair retention performance of rats given a mild-intensity footshock that resulted in only weak, non-contextual memory. These findings strongly suggest that corticosterone selectively impaired retrieval of contextual information associated with the training context. The centrally acting beta-adrenoceptor antagonist propranolol (2.0mg/kg), co-administered in a dose that did not affect retention performance alone, blocked the impairment in contextual memory retrieval induced by corticosterone. These findings provide evidence for the view that glucocorticoids interact with noradrenergic mechanisms in influencing memory retrieval.     

Repeated reminders inrease the speed of memory retrieval by 3‐month‐old infants

In two experiments, we examined the effect of repeated reminder treatments on the speed of memory retrieval by 3‐month‐old human infants. Infants were trained for two consecutive days to kick their feet to produce movement in an overhead mobile. Infants in the one‐reminder condition received a 3 min reminder treatment 13 days after the conclusion of training. Infants in the two‐reminder condition received one 3 min reminder treatment 6 days after the conclusion of training and a second reminder treatment 7 days later (i.e. 13 days following the conclusion of training). Infants in the no‐reminder control condition were not exposed to the reminder prior to the long‐term retention test. In the absence of a reminder treatment, infants exhibited complete forgetting during the long‐term test. Infants exposed to one reminder exhibited retention when tested 24 h after their only reminder, but not when tested earlier. Infants exposed to two reminder treatments, on the other hand, exhibited retention when tested 1, 4 or 24 h after their second reminder treatment. We conclude that the opportunity to retrieve the memory on a prior occasion facilitated subsequent memory retrieval.     

The context counts: Congruent learning and testing environments prevent memory retrieval impairment following stress

Stress before retention testing impairs memory, whereas memory performance is enhanced when the learning context is reinstated at retrieval. In the present study, we examined whether the negative impact of stress before memory retrieval can be attenuated when memory is tested in the same environmental context as that in which learning took place. Subjects learned a 2-D object location task in a room scented with vanilla. Twenty-four hours later, they were exposed to stress or a control condition before memory for the object location task was assessed in a cued-recall test, either in the learning context or in a different context (unfamiliar room without the odor). Stress impaired memory when assessed in the unfamiliar context, but not when assessed in the learning context. These results suggest that the detrimental effects of stress on memory retrieval can be abolished when a distinct learning context is reinstated at test.     

Contextual determinants of retrieval in three-month-old infants

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.     

Memory by association: Integrating memories prolongs retention by two-year-olds

Recalling one memory often leads to the recollection of other memories that share overlapping features. This phenomenon, spreading activation, was originally documented in studies conducted with verbal adults, and more recently, it has been demonstrated with preverbal infants. Here, we examine the effect of spreading activation on long-term retention by 2-year-olds. Participants were tested in the Visual Recognition Memory (VRM) paradigm and the deferred imitation paradigm. Typically, infants of this age exhibit retention in the VRM paradigm for 24 h, while they exhibit retention in the deferred imitation paradigm for at least 8 weeks. In the present experiment, we paired these tasks together during original encoding and tested infants after an 8-week delay. Two-year-olds exhibited retention in both tasks. That is, when these two tasks initially occurred together – one task that is extremely memorable and one that is not – retrieving the memory of the more memorable task cued retrieval of the less memorable task, extending its longevity.     

Hippocampal formation lesions impair performance in an odor-odor association task independently of spatial context

The rodent hippocampal system is known to play an important role in memory. Evidence that this role is not limited to spatial memory has come from studies using a variety of non-spatial memory tasks. One example is the social transmission of food preference paradigm, a task in which rats learn an odor-odor association with no explicit spatial memory component. However, because training and testing in this task typically take place in the same environment, it is possible that memory for the spatial context in which odors are experienced during training is critical to subsequent retention performance. If this is the case, it might be expected that lesions of the hippocampal system would impair memory performance by disrupting the establishment of a representation of the training environment. We addressed this issue by training rats in one spatial context and then testing them either in the same or a different spatial context. Normal control rats performed equally well when tested in an environment that was the same or different from that used during training, and the retention impairment exhibited by rats with hippocampus plus subiculum lesions was equivalent in the two test environments. These results support the view that the hippocampal system is necessary for the flexible expression of nonspatial memories even when the spatial context in which the memory is acquired is not critical to retrieval.     

The Influence of Retention Interval on the US Preexposure Effect: Changes in Contextual Blocking over Time

A number of studies manipulating the length of the interval between conditioning and testing indicate spontaneous recovery from overshadowing, suggesting that certain instances of overshadowing represent a deficit in memory retrieval rather than a failure of animals to form an association between the overshadowed stimulus and the US. The present series of experiments examined the influence of lengthening the retention interval on blocking, another stimulus selection phenomenon that is typically interpreted as an acquisition deficit. The results indicated that when subjects were tested shortly (3 days) after training conditioning to a taste blocked subsequent conditioning to an odor conditioned in compound with that taste (Experiment 1), whereas prior conditioning to an odor did not block subsequent conditioning to a taste conditioned in compound with that odor (Experiment 2). This pattern of results was essentially unchanged when testing occurred at a longer (21-day) retention interval. However, there was evidence of a US preexposure effect in Experiment 2 when subjects in the US ONLY control condition were tested at the 3-day retention interval, but not when testing occurred 21 days after conditioning. Experiments 3 and 4 examined whether this loss of the US preexposure effect over time might actually represent a change in the degree of contextual blocking as the retention interval is lengthened. Exposure to the conditioning context either during the interval between Phase 1 and Phase 2 of conditioning (Experiment 3) or prior to Phase 1 of conditioning (Experiment 4) alleviated this US preexposure effect suggesting that the loss of the US preexposure effect as the retention interval is lengthened observed in Experiment 2 is due to changes in the degree of blocking by contextual stimuli over time. The results are discussed in terms of differential susceptibility of forgetting of two functional roles played by a contextual stimuli in the current situation-context as a CS and context as a retrieval cue for other CS-US associations.     

Actions speak louder than words: Differences in memory flexibility between monolingual and bilingual 18‐month‐olds

Bilingual infants from 6‐ to 24‐months of age are more likely to generalize, flexibly reproducing actions on novel objects significantly more often than age‐matched monolingual infants are. In the current study, we examine whether the addition of novel verbal labels enhances memory generalization in a perceptually complex imitation task. We hypothesized that labels would provide an additional retrieval cue and aid memory generalization for bilingual infants. Specifically, we hypothesized that bilinguals might be more likely than monolinguals to map multiple perceptual features onto a novel label and therefore show enhanced generalization. Eighty‐seven 18‐month‐old monolingual and bilingual infants were randomly assigned to one of two experimental conditions or a baseline control condition. In the experimental conditions, either no label or a novel label was added during demonstration and again at the beginning of the test session. After a 24‐hr delay, infants were tested with the same stimulus set to test cued recall and with a perceptually different but functionally equivalent stimulus set to test memory generalization. Bilinguals performed significantly above baseline on both cued recall and memory generalization in both experimental conditions, whereas monolinguals performed significantly above baseline only on cued recall in both experimental conditions. These findings show a difference between monolinguals and bilinguals in memory generalization and suggest that generalization differences between groups may arise from visual perceptual processing rather than linguistic processing. A video abstract of this article can be viewed at https://youtu.be/yXB4pM3fF2k     

Motion tracking of parents’ infant‐ versus adult‐directed actions reveals general and action‐specific modulations

Parents tend to modulate their movements when demonstrating actions to their infants. Thus far, these modulations have primarily been quantified by human raters and for entire interactions, thereby possibly overlooking the intricacy of such demonstrations. Using optical motion tracking, the precise modulations of parents’ infant‐directed actions were quantified and compared to adult‐directed actions and between action types. Parents demonstrated four novel objects to their 14‐month‐old infants and adult confederates. Each object required a specific action to produce a unique effect (e.g. rattling). Parents were asked to demonstrate an object at least once before passing it to their demonstration partner, and they were subsequently free to exchange the object as often as desired. Infants’ success at producing the objects’ action‐effects was coded during the demonstration session and their memory of the action‐effects was tested after a several‐minute delay. Indicating general modulations across actions, parents repeated demonstrations more often, performed the actions in closer proximity and demonstrated action‐effects for longer when interacting with their infant compared to the adults. Meanwhile, modulations of movement size and velocity were specific to certain action‐effect pairs. Furthermore, a ‘just right’ modulation of proximity was detected, since infants’ learning, memory, and parents’ prior evaluations of their infants’ motor abilities, were related to demonstrations that were performed neither too far from nor too close to the infants. Together, these findings indicate that infant‐directed action modulations are not solely overall exaggerations but are dependent upon the characteristics of the to‐be learned actions, their effects, and the infant learners.     

Alcohol-induced state-dependent learning: Differentiating stimulus and storage hypotheses

State-dependent effects of alcohol have been demonstrated in animals and man. Most studies have used tasks for which accurate performance typically requires that stimulus input was adequately stored initially and that the items were retrieved at the time of testing. Thus an alcohol-induced decrement in performance could be due to impaired storage, impaired retrieval, or both. The purpose of this experiment was to distinguish between stimulus and storage hypotheses of state-dependent learning (SDL). Sixteen subjects were used in a 2×2 design in which the task involved the learning and recall of a 19-item ‘route’ map. During initial learning, all subjects were sober. Immediately after learning, half the subjects were given a moderate dose of alcohol. Twenty-four hours later, all subjects were tested for recall under the same or different conditions. Greater retention was found for those subjects whose drug states were the same in memory storage/consolidation and retrieval. Thus an alcohol state effective during the memory consolidation interval following acquisition appears to be a sufficient condition for producing SDL. In this context, SDL might be better termed state-dependent memory storage and retrieval. The implications of these results for the aetiology and treatment of alcohol dependence are discussed.     

Reinstatement versus reactivation effects on active memory in infants

Reinstatement and reactivation are procedurally different reminder paradigms used with infants and children, but most developmental psychologists do not distinguish between them. In 4 experiments with 102 three-month-olds, we asked if they differ functionally as well. Independent groups of infants received either a reactivation or a reinstatement reminder 3 days after training, when the memory is active, but its specific details have been forgotten. In Experiment 1, we measured retention after increasing delays until infants forgot altogether. A single reinstatement protracted retention twice as long after training as a single reactivation. In Experiments 2-4, whether the reminder was the original training stimulus or a novel one differentially affected the duration and specificity of memory in the 2 procedures as well. These data demonstrate that the distinction between reinstatement and reactivation is not artificial. In addition to differing procedurally, reinstatement and reactivation differ functionally, with different memory-preserving effects.     

Exploring memory in infancy: deferred imitation and the development of declarative memory

Imitation is an important means by which infants learn new behaviours. When infants do not have the opportunity to immediately reproduce observed actions, they may form a memory representation of the event which can guide their behaviour when a similar situation is encountered again. Imitation procedures can, therefore, provide insight into infant memory. The deferred imitation paradigm requires a modelled action to be reproduced following a delay, without prior motor practice. As such, deferred imitation procedures have been proposed to tap declarative memory abilities in non‐verbal populations such as infants. Contrary to the popular belief that infants form sparse or ill‐defined memories, deferred imitation research reveals that infants store and retrieve highly detailed memory representations. The specificity of detail encoded into the representation can, however, cause memory retrieval to fail at young ages. Developing the ability to identify event components which are central (the target stimulus) versus details which are peripheral (the exact context in which learning occurred) is therefore an important aspect of memory development. Using deferred imitation procedures to study the transition from constrained to flexible memory representations can thus facilitate our understanding of the development of declarative memory during the infancy period. Copyright © 2006 John Wiley & Sons, Ltd.     

Memory retrieval as a self-propagating process

Retrieval of a subset of studied items and the presentation of those items as retrieval cues typically impair retrieval of the other items. Previous research on this self-limiting property of memory retrieval has relied heavily on short retention intervals and similar context between encoding and test. Here, we examined retrieval dynamics also after a prolonged retention interval with different spatial and social context between encoding and test, conditions that mimic people’s remembering in many situations of daily life. For both unrelated word lists and more integrated prose material, we found retrieval and cuing to impair recall of other studied items after a short retention interval, but to improve recall in the prolonged retention interval condition. The results demonstrate that retrieval dynamics depend critically on situation, indicating that quite often in daily life, retrieval may be a self-propagating, rather than a self-limiting process.     

Reactivated memory of an inhibitory avoidance response in mice is sensitive to a nitric oxide synthase inhibitor

It is accepted that once consolidation is completed memory becomes permanent. However, it has also been suggested that reactivation (retrieval) of the original memory, again, makes it sensitive to the same treatments that affect memory consolidation when given after training. Previous results demonstrated that the immediate post-training intraperitoneal administration of N^ω-nitro-l-arginine methyl ester (L-NAME), a non-specific inhibitor of nitric oxide synthase (NOS), impairs retention test performance of a one-trial step-through inhibitory avoidance response in adult mice. The effect of L-NAME on retention was attributed to an action on memory consolidation of the original learning. For the first time, we report that the administration of L-NAME after the first retention test (memory reactivation) of the inhibitory avoidance response impairs retention performance over six consecutive days. This impairment effect is dose-and-time dependent and could not be attributed to a retrieval deficit since a mild footshock did not reinstate the original avoidance response and no spontaneous recovery was observed at least 21 days after training. Further support for a storage deficit interpretation as opposed to a retrieval deficit was obtained from the fact that L-NAME’s effects after retrieval were not due to state-dependency. The impairment effect of L-NAME was dependent on the age of the original memory. That is, there was an inverse correlation between the susceptibility of the memory trace when reactivated and the time elapsed between training and the first retrieval session. We suggest an action of L-NAME on memory reactivation-induced processes that are different from memory extinction of the original learning extending the biological significance of nitric oxide on memory.     

Long-term memory,forgetting, and deferred imitation in 12-month-old infants

Long-term recall memory, as indexed by deferred imitation, was assessed in 12-month-old infants. Independent groups of infants were tested after retention intervals of 3 min, 1 week and 4 weeks. Deferred imitation was assessed using the ‘observation-only’ procedure in which infants were not allowed motor practice on the tasks before the delay was imposed. Thus, the memory could not have been based on re-accessing a motor habit, because none was formed in the first place. After the delay, memory was assessed either in the same or a different environmental context from the one in which the adult had originally demonstrated the acts. In Experiments 1 and 3, infants observed the target acts while in an unusual environment (an orange and white polka-dot tent), and recall memory was tested in an ordinary room. In Experiment 2, infants observed the target acts in their homes and were tested for memory in a university room. The results showed recall memory after all retention intervals, including the 4 week delay, with no effect of context change. Interestingly, the forgetting function showed that the bulk of the forgetting occurred during the first week. The findings of recall memory without motor practice support the view that infants as young as 12 months old use a declarative (nonprocedural) memory system to span delay intervals as long as 4 weeks.     

d-Cycloserine: effects on long-term retention of a conditioned response and on memory for contextual attributes.

d-Cycloserine (DCS), a partial agonist of the glycine recognition site of the N-methyl d-aspartate receptor, has beneficial effects on learning and memory. In order to investigate its potential to influence learning and memory of both the response and the stimulus attributes of training, male Sprague-Dawley albino rats were trained in a one-trial inhibitory avoidance task following an acute intraperitoneal injection of DCS (3 mg/kg) or an equal volume of saline. In order to measure memory for stimulus attributes, testing involved a context shift paradigm, in which subjects are tested in either the environment of training or a different one. Good memory for the contextual attributes of training is indicated by poor performance in the alternate context. Retention was assessed either 1, 7, or 14 days after training. At 1 day, Saline subjects were affected by a change in context, while DCS subjects were not. In subjects tested 1 week following training, Saline subjects were no longer affected by a change in context, in that they performed the avoidance response in both contexts. This indicates the forgetting of stimulus attributes in Saline subjects. DCS subjects did show the context shift effect at 1 week, indicating the retention of stimulus attributes. Finally, Saline subjects demonstrated the context shift rebound at 14 days, while DCS subjects performed equivalently in both contexts. Taken together, these data suggest that DCS may enhance retention of fear and slow the forgetting of stimulus attributes.     

Time-dependent changes in inaccessible memory

The present experiment examined whether forgetting of contextual attributes—the loss of discriminability of background stimulus features over time—also occurs when a memory remains inaccessible (amnestic) during the retention interval. To examine this issue, rats received an acute hypothermia treatment that caused reversible anterograde amnesia for a passive-avoidance task and were tested 1 or 7 days later in either the same or a different context. At the short retention interval, the subjects discriminated between the contexts, as evidenced by the finding that reversal of amnesia occurred only in the training context. However, at the 7-day interval, recovery of the avoidance response was induced in either context, reflecting the forgetting of differentiating characteristics. These findings indicate that inaccessible memory remains susceptible to processes of modification and distortion that typically influence intact memories.