The role of sensory preconditioning in memory retrieval by preverbal infants

Cling together, swing together? Assessing indirect retrieval of stimulus-response bindings for associated stimuli

When a stimulus is paired with a response, a stimulus-response (SR) binding (or event file) is formed. Subsequent stimulus repetition retrieves the SR binding from memory, which facilitates (impedes) performance when the same (a different) response is required. We aimed to explore whether indirect retrieval of SR bindings by a newly learnt associated stimulus is possible. Participants first went through a learning task to acquire novel stimulus-stimulus associations. The same stimulus pairs were then presented in a prime-probe task to assess direct and indirect retrieval effects. Participants responded by classifying word color in prime and probe trials. Probe words were either identical to prime words (test for direct retrieval) or corresponded to the associated stimulus (test for indirect retrieval) or were unrelated words (baseline). Independently of word relation, response relation (repetition vs. change) across prime and probe trials was manipulated. In two highly powered preregistered studies (total N = 260) using different types of stimulus associations, we obtained evidence for direct retrieval due to identical word repetition in the probe. Crucially, evidence for indirect retrieval upon presentation of an associated probe word was absent. Controlling for memory of each stimulus-stimulus association did not alter the findings. Our results show that indirect retrieval through newly acquired associations does not occur at the level of SR bindings, at least not for recently acquired stimulus-stimulus associations. Our study illustrates the scope of binding principles and highlights boundary conditions for the stimulus properties that can elicit automatic response retrieval.

One Link to Link Them All

A conditioned response to a stimulus can be transferred to an associated stimulus, as seen in sensory preconditioning. In this research paper, we aimed to explore this phenomenon using a stimulus-response contingency learning paradigm using voluntary actions as responses. We conducted two preregistered experiments that explored whether a learned response can be indirectly activated by a stimulus (S1) that was never directly paired with the response itself. Importantly, S1 was previously associated with another stimulus (S2) that was then directly and contingently paired with a response (S2-R contingency). In Experiment 1a, an indirect activation of acquired stimulus-response contingencies was present for audiovisual stimulus pairs wherein the stimulus association resembled a vocabulary learning setup. This result was replicated in Experiment 1b. Additionally, we found that the effect is moderated by having conscious awareness of the S1-S2 association and the S2-R contingency. By demonstrating indirect activation effects for voluntary actions, our findings show that principles of Pavlovian conditioning like sensory preconditioning also apply to contingency learning of stimulus-response relations for operant behavior.

Dynamic developmental changes in neurotransmitters supporting infant attachment learning

Infant survival relies on rapid identification, remembering and behavioral responsiveness to caregivers' sensory cues. While neural circuits supporting infant attachment learning have largely remained elusive in children, use of invasive techniques has uncovered some of its features in rodents. During a 10-day sensitive period from birth, newborn rodents associate maternal odors with maternal pleasant or noxious thermo-tactile stimulation, which gives rise to a preference and approach behavior towards these odors, and blockade of avoidance learning. Here we review the neural circuitry supporting this neonatal odor learning, unique compared to adults, focusing specifically on the early roles of neurotransmitters such as glutamate, GABA (Gamma-AminoButyric Acid), serotonin, dopamine and norepinephrine, in the olfactory bulb, the anterior piriform cortex and amygdala. The review highlights the importance of deepening our knowledge of age-specific infant brain neurotransmitters and behavioral functioning that can be translated to improve the well-being of children during typical development and aid in treatment during atypical development in childhood clinical practice, and the care during rearing of domestic animals.

Associations between Bilingualism and Memory Generalization During Infancy: Does Socioeconomic Status Matter?

Past studies have reported memory differences between monolingual and bilingual infants (Brito & Barr, 2012; Singh et al., 2015). A common critique within the bilingualism literature is the absence of socioeconomic indicators and/or a lack of socioeconomic diversity among participants. Previous research has demonstrated robust bilingual differences in memory generalization from 6- to 24-months of age. The goal of the current study was to examine if these findings would replicate in a sample of 18-month-old monolingual and bilingual infants from a range of socioeconomic backgrounds (N = 92). Results indicate no differences between language groups on working memory or cued recall, but significant differences for memory generalization, with bilingual infants outperforming monolingual infants regardless of socioeconomic status (SES). These findings replicate and extend results from past studies (Brito & Barr, 2012; Brito, Sebastián-Gallés, & Barr, 2015) and suggest possible differential learning patterns dependent on linguistic experience.

Second-Order Correlation Learning of Dynamic Stimuli: Evidence from Infants and Computational Modeling

We present two habituation experiments that examined 20- and 26-month-olds' ability to engage in second-order correlation learning for static and dynamic features, whereby learned associations between two pairs of features (e.g., P and Q, P and R) are generalized to the features that were not presented together (e.g., Q and R). We also present results from an associative learning mechanism that was implemented as an autoencoder parallel distributed processing (PDP) network in which second-order correlation learning is shown to be an emergent property of the dynamics of the network. The experiments and simulation demonstrate that 20- and 26-month-olds as well as neural networks are capable of second-order correlation learning in a category context for internal features of dynamic objects. However, the model predicts-and Experiment 3 demonstrates-that 20- and 26-month-olds are unable to encode second-order correlations in a noncategory context for dynamic objects with internal features. It is proposed that the ability to learn second-order correlations represents a powerful but as yet unexplored process for generalization in the first years of life.

Human Consciousness: Where Is It From and What Is It for

Consciousness is not a process in the brain but a kind of behavior that, of course, is controlled by the brain like any other behavior. Human consciousness emerges on the interface between three components of animal behavior: communication, play, and the use of tools. These three components interact on the basis of anticipatory behavioral control, which is common for all complex forms of animal life. All three do not exclusively distinguish our close relatives, i.e., primates, but are broadly presented among various species of mammals, birds, and even cephalopods; however, their particular combination in humans is unique. The interaction between communication and play yields symbolic games, most importantly language; the interaction between symbols and tools results in human praxis. Taken together, this gives rise to a mechanism that allows a creature, instead of performing controlling actions overtly, to play forward the corresponding behavioral options in a “second reality” of objectively (by means of tools) grounded symbolic systems. The theory possesses the following properties: (1) It is anti-reductionist and anti-eliminativist, and yet, human consciousness is considered as a purely natural (biological) phenomenon. (2) It avoids epiphenomenalism and indicates in which conditions human consciousness has evolutionary advantages, and in which it may even be disadvantageous. (3) It allows to easily explain the most typical features of consciousness, such as objectivity, seriality and limited resources, the relationship between consciousness and explicit memory, the feeling of conscious agency, etc.

Transitions in the temporal parameters of sensory preconditioning during infancy

Sensory preconditioning (SPC) is a form of latent learning in which preexposure to co-occurring neutral stimuli (S1 -S2 ) permits subsequent learning to be transferred from one stimulus (S1 ) to the other (S2 ). We examined whether human infants exhibit developmental transitions in the temporal parameters of SPC by manipulating the preexposure regimen. Infants received simultaneous or sequential preexposure to puppets S1 and S2 (Days 1-2); saw target actions modeled on S1 (Day 3); and were tested for deferred imitation with S2 (Day 4). Although 6-, 9-, and 12-month-olds associated the puppets, there was a shift in the effective regimen from simultaneous to sequential preexposure-similar to prior findings with rat pups (Experiment 1). Experiment 2 revealed that human infants potentially exhibit another transition in SPC at 15 and 18 months of age. We consider the roles of ontogenetic shifts in infants' ecological niche, selective attention, and unitization in developmental transitions in SPC.

Seeing the unseen: Second-order correlation learning in 7- to 11-month-olds

We present four experiments with the object-examining procedure that investigated 7-, 9-, and 11-month-olds' ability to associate two object features that were never presented simultaneously. In each experiment, infants were familiarized with a number of 3D objects that incorporated different correlations among the features of those objects and the body of the objects (e.g., Part A and Body 1, and Part B and Body 1). Infants were then tested with objects with a novel body that either possessed both of the parts that were independently correlated with one body during familiarization (e.g., Part A and B on Body 3) or that were attached to two different bodies during familiarization. The experiments demonstrate that infants as young as 7months of age are capable of this kind of second-order correlation learning. Furthermore, by at least 11months of age infants develop a representation for the object that incorporates both of the features they experienced during training. We suggest that the ability to learn second-order correlations represents a powerful but as yet largely unexplored process for generalization in the first years of life.

The extended trajectory of hippocampal development: Implications for early memory development and disorder

Hippocampus has an extended developmental trajectory, with refinements occurring in the trisynaptic circuit until adolescence. While structural change should suggest a protracted course in behavior, some studies find evidence of precocious hippocampal development in the first postnatal year and continuity in memory processes beyond. However, a number of memory functions, including binding and relational inference, can be cortically supported. Evidence from the animal literature suggests that tasks often associated with hippocampus (visual paired comparison, binding of a visuomotor response) can be mediated by structures external to hippocampus. Thus, a complete examination of memory development will have to rule out cortex as a source of early memory competency. We propose that early memory must show properties associated with full function of the trisynaptic circuit to reflect "adult-like" memory function, mainly (1) rapid encoding of contextual details of overlapping patterns, and (2) retention of these details over sleep-dependent delays. A wealth of evidence suggests that these functions are not apparent until 18-24 months, with behavioral discontinuities reflecting shifts in the neural structures subserving memory beginning approximately at this point in development. We discuss the implications of these observations for theories of memory and for identifying and measuring memory function in populations with typical and atypical hippocampal function.

Learning to remember: the early ontogeny of episodic memory

Over the past 60 years the neural correlates of human episodic memory have been the focus of intense neuroscientific scrutiny. By contrast, neuroscience has paid substantially less attention to understanding the emergence of this neurocognitive system. In this review we consider how the study of memory development has evolved. In doing so, we concentrate primarily on the first postnatal year because it is within this time window that the most dramatic shifts in scientific opinion have occurred. Moreover, this time frame includes the critical age (∼9 months) at which human infants purportedly first begin to demonstrate rudimentary hippocampal-dependent memory. We review the evidence for and against this assertion, note the lack of direct neurocognitive data speaking to this issue, and question how demonstrations of exuberant relational learning and memory in infants as young as 3-months old can be accommodated within extant models. Finally, we discuss whether current impasses in the infant memory literature could be leveraged by making greater use of neuroimaging techniques, such as magnetic resonance imaging (MRI), which have been deployed so successfully in adults.

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.

Neural correlates of sensory preconditioning: a preliminary fMRI investigation

Sensory preconditioning (SPC; also known as behaviorally silent learning) consists of a combination of two neutral stimuli, none of which elicits an unconditional response. After one of them is later paired with an unconditional stimulus (US), the other neutral stimulus also yields a conditional response although it has never been paired with the US. In this study, an event-related functional magnetic resonance imaging (fMRI) paradigm was used to specify brain regions involved in SPC. The results demonstrated that SPC was associated with significant changes in activity of several regions, notably, the left amygdala, the left hippocampus, the bilateral thalamus, the bilateral medial globus pallidus, the bilateral cerebellum, the bilateral premotor cortex, and the bilateral middle frontal gyrus. This is a first effort to use fMRI to examine the effects of SPC on brain activation. Our data suggest that there is a distributed network of structures involved in SPC including both cortical and subcortical regions, therefore add to our understanding of the neural mechanisms underlying the ability to associative learning.

Age-related differences in memory expression during infancy: using eye-tracking to measure relational memory in 6- and 12-month-olds

Relational memory, or the ability to bind components of an event into a network of linked representations, is a primary function of the hippocampus. Here we extend eye-tracking research showing that infants are capable of forming memories for the relation between arbitrarily paired scenes and faces, by looking at age-related changes in relational memory over the first year of life. Six- and 12-month-old infants were familiarized with pairs of faces and scenes before being tested with arrays of three familiar faces that were presented on a familiar scene. Preferential looking at the face that matches the scene is typically taken as evidence of relational memory. The results showed that while 6-month-old showed very early preferential looking when face/scene pairs were tested immediately, 12-month-old did not exhibit evidence of relational memory either immediately or after a short delay. Theoretical implications for the functional development of the hippocampus and practical implications for the use of eye tracking to measure memory during early life are discussed.

Sensory preconditioning in newborn rabbits: from common to distinct odor memories

This study evaluated whether olfactory preconditioning is functional in newborn rabbits and based on joined or independent memory of odorants. First, after exposure to odorants A+B, the conditioning of A led to high responsiveness to odorant B. Second, responsiveness to B persisted after amnesia of A. Third, preconditioning was also functional with two overlapping pairs of odorants (A+B and B+C) and amnesia of one odorant did not affect memory of the others. Thus, incidental pairing of odorants allows reinforcement of one odorant to implicitly reinforce the others, the bond then vanishes, and the memory of each element becomes independent.

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.

Infant long-term memory for associations formed during mere exposure

We previously found that young infants spontaneously associate stimuli that they merely see together. Using a sensory preconditioning paradigm with 6- and 9-month-olds, we asked how long such associations remain latent before being forgotten and what exposure conditions affect their persistence. Groups were preexposed to two puppets for 1h/day for 2 days, 1h on 1 day, or 1h on 1 day in two sessions; 1-27 days later, target actions were modeled on one puppet, and infants were tested with the other puppet 1 day later. The longest delay after which infants imitated the actions on the other puppet defined how long they remembered the association. The data revealed that the preexposure regimen determined retention. Regardless of exposure time, both ages remembered the association longer after two sessions, and younger infants remembered longer than older infants--for 4 weeks--after two 30-min sessions on 1 day.

Infants' meaning-making and the development of mental health problems

We argue that infant meaning-making processes are a central mechanism governing both typical and pathological outcomes. Infants, as open dynamic systems, must constantly garner information to increase their complexity and coherence. They fulfill this demand by making nonverbal "meaning"-affects, movements, representations-about themselves in relation to the world and themselves into a "biopsychosocial state of consciousness," which shapes their ongoing engagement with the world. We focus on the operation of the infant-adult communication system, a dyadic, mutually regulated system that scaffolds infants' engagement with the world of people, things, and themselves, and consequently their meaning-making. We argue that infant mental health problems emerge when the meanings infants make in the moment, which increase their complexity and coherence and may be adaptive in the short run, selectively limit their subsequent engagement with the world and, in turn, the growth of their state of consciousness in the long run. When chronic and iterative, these altered meanings can interfere with infants' successful development and heighten their vulnerability to pathological outcomes. Cultural variations in meaning-making and implications for clinical practice are discussed.

The neurobiology of infant maternal odor learning

Infant rats must learn to identify their mother's diet-dependent odor. Once learned, maternal odor controls pups' approach to the mother, their social behavior and nipple attachment. Here we present a review of the research from four different laboratories, which suggests that neural and behavioral responses to the natural maternal odor and neonatal learned odors are similar. Together, these data indicate that pups have a unique learning circuit relying on the olfactory bulb for neural plasticity and on the hyperfunctioning noradrenergic locus coeruleus flooding the olfactory bulb with norepinephrine to support the neural changes. Another important factor making this system unique is the inability of the amygdala to become incorporated into the infant learning circuit. Thus, infant rats appear to be primed in early life to learn odors that will evoke approach responses supporting attachment to the caregiver.

Why a neuromaturational model of memory fails: exuberant learning in early infancy

The characteristics of memory in infants and adults seem vastly different. The neuromaturational model attributes these differences to an ontogenetic change in the basic memory process, namely, to the hierarchical maturation of two distinct memory systems. The early-maturing (implicit) system is functional during the first third of infancy and supports the gradual learning of perceptual and motor skills; the late-maturing (explicit) system supports representations of contextually specific events, relationships, and associations. An alternative model holds that the basic memory process does not change, but what infants and adults select to encode for learning does. This ontogenetic change in selective attention has been mistaken for an ontogenetic shift in the basic memory process. Over the last 25 years, evidence from transfer studies with developing rats and human infants has revealed that the first third of infancy is actually a period of exuberant learning that ends, not coincidentally, at the same age that the late-maturing memory system presumably emerges. This article reviews data from recent studies of sensory preconditioning, potentiation, associative chains, and transitive inference with human infants that support this conclusion-data for which the neuromaturational model cannot account. Fast mapping is a general learning mechanism that accounts for this evidence.

Peculiar modulation of taste aversion learning by the time of day in developing rats

The ontogeny of the temporal context modulation of conditioned taste aversion was studied in male Wistar rats using a palatable 1% NaCl solution. A procedure that included two saline preexposures, a single pairing saline-lithium chloride (0.15 M; 1% b.w.) either at the same or a different time of day of preexposures and a one-bottle test at the same time than preexposure was applied. Four age groups (PN32, PN48, PN64, and PN100) covering the complete range from adolescence to the adult period were tested. The results showed no effect of a temporal context shift in PN32. A peculiar enhancement of temporal context-specific saline aversions was exhibited by PN48 and PN64 rats, while the adult typical temporal context specificity of latent inhibition was only evident in PN100 rats. The results are discussed in terms of the peculiar brain functional organization during a protracted adolescence period.

Multiple memory systems are unnecessary to account for infant memory development: an ecological model

How the memory of adults evolves from the memory abilities of infants is a central problem in cognitive development. The popular solution holds that the multiple memory systems of adults mature at different rates during infancy. The early-maturing system (implicit or nondeclarative memory) functions automatically from birth, whereas the late-maturing system (explicit or declarative memory) functions intentionally, with awareness, from late in the first year. Data are presented from research on deferred imitation, sensory preconditioning, potentiation, and context for which this solution cannot account and present an alternative model that eschews the need for multiple memory systems. The ecological model of infant memory development (N. E. Spear, 1984) holds that members of all species are perfectly adapted to their niche at each point in ontogeny and exhibit effective, evolutionarily selected solutions to whatever challenges each new niche poses. Because adults and infants occupy different niches, what they perceive, learn, and remember about the same event differs, but their raw capacity to learn and remember does not.

Accounting for change in declarative memory: A cognitive neuroscience perspective

The medial temporal lobe memory system matures relatively early and supports rudimentary declarative memory in young infants. There is considerable development, however, in the memory processes that underlie declarative memory performance during infancy. Here we consider age-related changes in encoding, retention, and retrieval in the context of current knowledge about the brain systems that may underlie these memory processes. While changes in infants' encoding may be attributed to rapid myelination during the first year of life, improvements in long-term retention and flexible retrieval are likely due to the prolonged development of the dentate gyrus. Future studies combining measures of brain and behavior are critical in improving our understanding of how brain development drives memory development during infancy and early childhood.

Infants form associations between memory representations of stimuli that are absent

Traditional models of learning assume that an association can be formed only between cues that are physically present. Here, we report that when two objects that had never appeared together were simultaneously activated in memory, young human infants associated the representations of those objects. Neither object was physically present at the time the association was formed. The association remained latent for up to 2 weeks, when the infants used it to perform a deferred imitation task. These findings reveal that what infants merely see "brings to mind" what they saw before and combines it in new ways. In addition to challenging a fundamental tenet of classic learning models, these findings have major theoretical and practical implications for early cognitive development. Every day, in the same manner, young infants probably form numerous associations between activated memories of objects that are physically absent, creating a potential knowledge base of untold dimensions.

Age-related changes in memory reactivation by 1- and 2-year-old human infants

In three experiments, we examined the effect of a single reactivation treatment on retention by 1- and 2-year-old human infants who were tested in the visual recognition memory (VRM) paradigm. In all experiments, infants were familiarized with a visual stimulus and were tested after a delay. In the absence of a reactivation treatment, infants of both ages exhibited forgetting but exposure to a reactivation treatment alleviated forgetting after the same delay. When the duration of the original familiarization period was only 10 s, the minimum duration of an effective reminder treatment was 1 s for 2-year-olds, but was 5 s for 1-year-olds. When the duration of the original familiarization period was increased to 30 s, however, a 1-s reminder also alleviated forgetting by 1-year-olds.

Repeated priming increases memory accessibility in infants

In previous research on priming (reactivation) with 3-month-olds, two primes recovered a forgotten memory faster than one, suggesting that prior priming had increased the accessibility of the forgotten memory. Exploiting the fact that the minimum duration of a prime indexes the accessibility of the forgotten memory, we currently examined whether prior priming also reduces the minimum effective prime duration. In three experiments, 60 3-month-olds learned an operant task, forgot it, and then were exposed to successive primes either 1 day and 1 week after forgetting (Experiment 1) or 1 and 2 weeks after forgetting (Experiment 2). In both cases, prior priming reduced the minimum duration of the second prime, a result that was independent of the duration of the first prime (Experiment 3). These findings confirm that priming increases the accessibility of a latent memory and raise the possibility that repeated priming underlies the extended memorability of persons and events that infants encounter sporadically.

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.

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.