Relational memory during infancy: evidence from eye tracking

Attention control in autism: Eye-tracking findings from pre-school children in a low- and middle-income country setting

LAY ABSTRACT

The development of cognitive processes, such as attention control and learning, has been suggested to be altered in children with a diagnosis of autism spectrum disorder. However, nearly all of our understanding of the development of these cognitive processes comes from studies with school-aged or older children in high-income countries, and from research conducted in a controlled laboratory environment, thereby restricting the potential generalisability of results and away from the majority of the world's population. We need to expand our research to investigate abilities beyond these limited settings. We address shortcomings in the literature by (1) studying attention control and learning in an understudied population of children in a low- and middle-income country setting in India, (2) focusing research on a critical younger age group of children and (3) using portable eye-tracking technology that can be taken into communities and healthcare settings to increase the accessibility of research in hard-to-reach populations. Our results provide novel evidence on differences in attention control and learning responses in groups of children with and without a diagnosis of autism spectrum disorder. We show that learning responses in children that we assessed through a portable eye-tracking task, called the 'antisaccade task', may be specific to autism. This suggests that the methods we use may have the potential to identify and assess autism-specific traits across development, and be used in research in low-resource settings.

OWLET: An automated, open-source method for infant gaze tracking using smartphone and webcam recordings

Groundbreaking insights into the origins of the human mind have been garnered through the study of eye movements in preverbal subjects who are unable to explain their thought processes. Developmental research has largely relied on in-lab testing with trained experimenters. This constraint provides a narrow window into infant cognition and impedes large-scale data collection in families from diverse socioeconomic, geographic, and cultural backgrounds. Here we introduce a new open-source methodology for automatically analyzing infant eye-tracking data collected on personal devices in the home. Using algorithms from computer vision, machine learning, and ecological psychology, we develop an online webcam-linked eye tracker (OWLET) that provides robust estimation of infants' point of gaze from smartphone and webcam recordings of infant assessments in the home. We validate OWLET in a large sample of 7-month-old infants (N = 127) tested remotely, using an established visual attention task. We show that this new method reliably estimates infants' point-of-gaze across a variety of contexts, including testing on both computers and mobile devices, and exhibits excellent external validity with parental-report measures of attention. Our platform fills a significant gap in current tools available for rapid online data collection and large-scale assessments of cognitive processes in infants. Remote assessment addresses the need for greater diversity and accessibility in human studies and may support the ecological validity of behavioral experiments. This constitutes a critical and timely advance in a core domain of developmental research and in psychological science more broadly.

Effects of early exposure to phthalates on cognitive development and visual behavior at 24 months

BACKGROUND AND OBJECTIVES

Studies focusing on the neurodevelopmental effects of phthalates seldom consider exposure during infancy, a critical period for brain development. Most rely on parent-completed questionnaires to assess child neurodevelopment, which may be subject to reporting error. We studied the associations between prenatal and infancy exposure to phthalates and objective measures of neurodevelopment at the age of two.

METHODS

We relied on 151 mother-child pairs from the SEPAGES mother-child cohort. Women were asked to collect three spot urine samples per day over seven consecutive days during the second (median: 18.0 gestational weeks) and third (median: 34.2 gestational weeks) trimesters of pregnancy. They then collected one urine sample per day over seven consecutive days from their infants around the age of 12 months. Metabolites of phthalates and non-phthalate plasticizers were measured in within-subject and within-period pools of repeated urine samples. Eye tracking tasks were performed at two years allowing to compute four indicators linked with cognitive development and visual behavior: mean fixation duration, novelty preference, percent time spent looking at the eyes and mean reaction time.

RESULTS

Pre-natal exposure to monobenzyl phthalate at the second and third trimesters was associated with shorter fixation durations. In models allowing for interaction with child sex, these associations were only observed among girls. Exposure to di(2-ethylhexyl) phthalate at the third but not the second trimester was associated with increased time spent looking at a novel face and eyes. We observed faster reaction times and decreased time spent looking at the eyes in a face recognition task, with increased post-natal exposure to monoethyl, mono-iso-butyl and mono-n-butyl phthalates.

DISCUSSION

Relying on improved exposure assessment, we highlighted associations of pre- and post-natal exposure to phthalates with indicators derived from eye tracking tasks, mainly in girls. Some of these indicators have been affected in individuals with neurodevelopmental disorders.

Offline Calibration for Infant Gaze and Head Tracking across a Wide Horizontal Visual Field

Most well-established eye-tracking research paradigms adopt remote systems, which typically feature regular flat screens of limited width. Limitations of current eye-tracking methods over a wide area include calibration, the significant loss of data due to head movements, and the reduction of data quality over the course of an experimental session. Here, we introduced a novel method of tracking gaze and head movements that combines the possibility of investigating a wide field of view and an offline calibration procedure to enhance the accuracy of measurements. A 4-camera Smart Eye Pro system was adapted for infant research to detect gaze movements across 126° of the horizontal meridian. To accurately track this visual area, an online system calibration was combined with a new offline gaze calibration procedure. Results revealed that the proposed system successfully tracked infants' head and gaze beyond the average screen size. The implementation of an offline calibration procedure improved the validity and spatial accuracy of measures by correcting a systematic top-right error (1.38° mean horizontal error and 1.46° mean vertical error). This approach could be critical for deriving accurate physiological measures from the eye and represents a substantial methodological advance for tracking looking behaviour across both central and peripheral regions. The offline calibration is particularly useful for work with developing populations, such as infants, and for people who may have difficulties in following instructions.

Predicting explicit memory for meaningful cartoons from visual paired comparison in infants and toddlers

We tested the memory of 18-, 33-, and 39-month-olds (N = 120) for dynamic stimulus material (simple cartoons) after 6 months in a visual paired comparison (VPC) task. We also tested the explicit recognition memory (ERM) for the same material. Only the oldest age group (39-month-olds) showed a significant visual (familiarity) preference at the test. Similarly, only the oldest group reliably chose the correct cartoon in the ERM test. Data from the VPC and ERM tasks did not correlate in any age group. However, we suggested a novel score (coined ΔVPC) measuring how much visual preference changes during the test phase in the VPC task. We found that this ΔVPC score (and vocabulary) predicted children's performance in the ERM task, whereas other potential predictors such as age and conventional novelty preference did not. We discuss the impact of these findings in relation to the development of implicit and explicit memory. Furthermore, we propose that VPC measures are associated with explicit memory only when the participants processed the stimuli conceptually. In such cases, we suggest that the ΔVPC score is an approximation of how demanding it is to construct the mental representation of the familiar stimulus during the test phase.

Evidence of hippocampal learning in human infants

The hippocampus is essential for human memory.¹ The protracted maturation of memory capacities from infancy through early childhood^2-4 is thus often attributed to hippocampal immaturity.^5-7 The hippocampus of human infants has been characterized in terms of anatomy,^8,9 but its function has never been tested directly because of technical challenges.^10,11 Here, we use recently developed methods for task-based fMRI in awake human infants¹² to test the hypothesis that the infant hippocampus supports statistical learning.^13-15 Hippocampal activity increased with exposure to visual sequences of objects when the temporal order contained regularities to be learned, compared to when the order was random. Despite the hippocampus doubling in anatomical volume across infancy, learning-related functional activity bore no relationship to age. This suggests that the hippocampus is recruited for statistical learning at the youngest ages in our sample, around 3 months. Within the hippocampus, statistical learning was clearer in anterior than posterior divisions. This is consistent with the theory that statistical learning occurs in the monosynaptic pathway,¹⁶ which is more strongly represented in the anterior hippocampus.^17,18 The monosynaptic pathway develops earlier than the trisynaptic pathway, which is linked to episodic memory,^19,20 raising the possibility that the infant hippocampus participates in statistical learning before it forms durable memories. Beyond the hippocampus, the medial prefrontal cortex showed statistical learning, consistent with its role in adult memory integration²¹ and generalization.²² These results suggest that the hippocampus supports the vital ability of infants to extract the structure of their environment through experience.

Autobiographical Memory in Autism Spectrum Disorder, Attention-Deficit/Hyperactivity Disorder, Hearing Loss, and Childhood Trauma: Implications for Social Communication Intervention

Purpose Speech-language pathologists (SLPs) work with a variety of populations at risk for poor autobiographical and episodic memory. The purpose of this tutorial is to describe autobiographical memory and how it is affected in children with autism spectrum disorder, attention-deficit/hyperactivity disorder, hearing loss, and childhood trauma, as well as provide clinicians with practical strategies for supporting autobiographical memory in each of these clinical populations. Method This tutorial reviews the literature on (a) autobiographical and episodic memory in typical development; (b) its relation to theory of mind, personal narrative skills, and executive functions; (c) elaborative reminiscing in typical development; (d) how autobiographical memory is impaired in children with autism spectrum disorder, attention-deficit/hyperactivity disorder, hearing loss, and childhood trauma; and (e) strategies for supporting autobiographical memory in each clinical population. Conclusions When adequately prepared, SLPs are uniquely situated to address autobiographical and episodic memory in their work with children, families, and related professionals. This is a long-overdue focus of such great clinical import that justifies its inclusion in the traditional training and preparation of SLPs. Adapting elaborative reminiscing strategies for use with various clinical populations is promising for facilitating healthy EM development and related cognitive functions.

Head and body structure infants' visual experiences during mobile, naturalistic play

Infants’ visual experiences are important for learning, and may depend on how information is structured in the visual field. This study examined how objects are distributed in 12-month-old infants’ field of view in a mobile play setting. Infants wore a mobile eye tracker that recorded their field of view and eye movements while they freely played with toys and a caregiver. We measured how centered and spread object locations were in infants’ field of view, and investigated how infant posture, object looking, and object distance affected the centering and spread. We found that far toys were less centered in infants’ field of view while infants were prone compared to when sitting or upright. Overall, toys became more centered in view and less spread in location when infants were looking at toys regardless of posture and toy distance. In sum, this study showed that infants’ visual experiences are shaped by the physical relation between infants’ bodies and the locations of objects in the world. However, infants are able to compensate for postural and environmental constraints by actively moving their head and eyes when choosing to look at an object.

Attentional Measures of Memory in Typically Developing and Hypoxic-Ischemic Injured Infants

Hypoxic–ischemic injury (HII) at birth has been found to relate to differences in development, including decreased memory performance. The current study assessed recognition memory in 6- and 12-month-old HII infants and typically developing (TD) infants using two eye-tracking paradigms well suited to explore explicit memory processes early in life: visual paired comparison (VPC) and relational memory (RM). During the VPC, infants were familiarized to a face and then tested for their novelty preference immediately and after a two-minute delay. At 6 months, neither HII nor TD showed a VPC novelty preference at immediate delay, but at 12 months, both groups did; after the two-minute delay, no group showed a novelty preference. During RM, infants were presented with blocks containing a learning phase with three different scene–face pairs, and a test phase with one of the three scenes and all three faces appearing simultaneously. When there was no interference from other scene–face pairs between learning and test, 6-month-old TD showed evidence of an early novelty preference, but when there was interference, they revealed an early familiarity preference. For 12-month-old TD, some evidence for a novelty preference during RM was seen regardless of interference. Although HII and TD showed similar recognition memory on the VPC, when looking at RM, HII infants showed subtle differences in their attention to the familiar and novel faces as compared to their TD peers, suggesting that there might be subtle differences in the underlying memory processing mechanisms between HII and TD. More work is needed to understand how these attentional patterns might be predictive of later memory outcomes.

Using head-mounted eye-trackers to study sensory-motor dynamics of coordinated attention

In this chapter, we introduce recent research using head-mounted eye-trackers to record sensory-motor behaviors at a high resolution and examine parent-child interactions at a micro-level. We focus on one important research topic in early social and cognitive development: how young children and their parents coordinate their visual attention in social interactions. We start by introducing head-mounted eye-tracking and recent studies conducted using this method. We then present two sets of novel analysis techniques that examine how manual actions of parents and children with and without hearing loss contribute to their attention coordination. In the first set of analyses, we investigated different pathways parents and children used to coordinate their visual attention in toy play. After that, we used Sankey diagrams to represent the temporal dynamics of parents' and children's manual actions prior to and during coordinated attention. These two sets of analyses allowed us to explore how participants' sensory-motor behaviors contribute to the establishment and maintenance of coordinated attention. More generally, head-mounted eye-tracking allows us to ask new questions and conduct new analyses that were not previously possible. With this new sensing technology, the results here highlight the importance of understanding early social interaction from a multimodal, embodied view.

An associative analysis of recognition memory: Relative recency effects in an eye-tracking paradigm

We report 2 eye-tracking experiments with human variants of 2 rodent recognition memory tasks, relative recency and object-in-place. In Experiment 1 participants were sequentially exposed to 2 images, A then B, presented on a computer display. When subsequently tested with both images, participants biased looking toward the first-presented image A: the relative recency effect. When contextual stimuli x and y, respectively, accompanied A and B in the exposure phase (xA, yB), the recency effect was greater when y was present at test, than when x was present. In Experiment 2 participants viewed 2 identical presentations of a 4-image array, ABCD, followed by a test with the same array, but in which one of the pairs of stimuli exchanged position (BACD or ABDC). Participants looked preferentially at the displaced stimulus pair: the object-in-place effect. Three further conditions replicated Experiment 1's findings: 2 pairs of images were presented one after the other (AB followed by CD); on a test with AB and CD, relative recency was again evident as preferential looking at AB. Moreover, this effect was greater when the positions of the first-presented A and B were exchanged between exposure and test (BACD), compared with when the positions of second-presented C and D were exchanged (ABDC). The results were interpreted within the theoretical framework of the Sometime Opponent Process model of associative learning (Wagner, 1981). (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Sleep-dependent memory consolidation in infants protects new episodic memories from existing semantic memories

Any experienced event may be encoded and retained in detail as part of our episodic memory, and may also refer and contribute to our generalized knowledge stored in semantic memory. The beginnings of this declarative memory formation are only poorly understood. Even less is known about the interrelation between episodic and semantic memory during the earliest developmental stages. Here, we show that the formation of episodic memories in 14- to 17-month-old infants depends on sleep, subsequent to exposure to novel events. Infant brain responses reveal that, after sleep-dependent consolidation, the newly stored events are not processed semantically, although appropriate lexical-semantic memories are present and accessible by similar events that were not experienced before the nap. We propose that temporarily disabled semantic processing protects precise episodic memories from interference with generalized semantic memories. Selectively restricted semantic access could also trigger semantic refinement, and thus, might even improve semantic memory.

Learning abilities

Learning abilities are present in infancy, as they are critical for adaptation. From simple habituation and novelty responses to stimuli, learning capacities evolve throughout the lifespan. During development, learning abilities become more flexible and integrated across sensory modalities, allowing the encoding of more complex information, and in larger amounts. In turn, an increasing knowledge base leads to adaptive changes in behavior, making responses and actions more precise and effective. The objective of this chapter is to review the main behavioral manifestations of human learning abilities in early development and their biologic underpinnings, ranging from the cellular level to neurocognitive systems and mechanisms. We first focus on the ability to learn from repetitions of stimuli and how years of research in this field have recently contributed to theories of fundamental brain mechanisms whose implications for cognitive development are under study. The ability to memorize associations between different items and events is addressed next as we review the variety of contexts in which this associative memory and its neurologic bases come into play. Together, repetition-based learning and associative memory provide powerful means of understanding the surrounding environment, not only through the gathering and consolidation of specific types of information, but also by continually testing and adjusting stored information to better adapt to changing conditions.

Persistence and Accumulation of Visual Memories for Objects in Scenes in 12-Month-Old Infants

Visual memory for objects has been studied extensively in infants over the past 20 years, however, little is known about how they are formed when objects are embedded in naturalistic scenes. In adults, memory for objects in a scene show information accumulation over time as well as persistence despite interruptions (Melcher, 2001, 2006). In the present study, eye-tracking was used to investigate these two processes in 12-month-old infants (N = 19) measuring: (1) whether longer encoding time can improve memory performance (accumulation), and (2) whether multiple shorter exposures to a scene are equivalent to a single exposure of the same total duration (persistence). A control group of adults was also tested in a closely matched paradigm (N = 23). We found that increasing exposure time led to gains in memory performance in both groups. Infants were found to be successful in remembering objects with continuous exposures to a scene, but unlike adults, were not able to perform better than chance when interrupted. However, infants' scan patterns showed evidence of memory as they continued the exploration of the scene in a strategic way following the interruption. Our findings provide insight into how infants are able to build representations of their visual environment by accumulating information about objects embedded in scenes.

Impaired relational memory in the early stage of psychosis

BACKGROUND

Humans constantly take in vast amounts of information, which must be filtered, flexibly manipulated, and integrated into cohesive relational memories in order to choose relevant behaviors. Relational memory is impaired in chronic schizophrenia, which has been linked to hippocampal dysfunction. It is unclear whether relational memory is impaired in the early stage of psychosis.

METHODS

We studied eye movements during a face-scene pairs task as an indirect measure of relational memory in 89 patients in the early stage of psychosis and 84 healthy control participants. During testing, scenes were overlaid with three equally-familiar faces and participants were asked to recall the matching (i.e. previously-paired) face. During Match trials, one face had been previously paired with the scene. During Non-Match trials, no faces matched the scene. Forced-choice explicit recognition was recorded as a direct measure of relational memory.

RESULTS

Healthy control subjects rapidly (within 250-500 ms) showed preferential viewing of the matching face during Match trials. In contrast, preferential viewing was delayed in patients in the early stage of psychosis. Explicit recognition of the matching face was also impaired in the patient group.

CONCLUSIONS

This study provides novel evidence for a relational memory deficit in the early stage of psychosis. Patients showed deficits in both explicit recognition as well as abnormal eye-movement patterns during memory recall. Eye movements provide a promising avenue for the study of relational memory in psychosis, as they allow for the assessment of rapid, nonverbal memory processes.

Eye tracking - The overlooked method to measure cognition in neurodegeneration?

Eye tracking (ET) studies are becoming increasingly popular due to rapid methodological and technological advances as well as the development of cost efficient and portable eye trackers. Although historically ET has been mostly employed in psychophysics or developmental cognition studies, there is also promising scope to use ET for movement disorders and measuring cognitive processes in neurodegeneration. Particularly, ET can be a powerful tool for cognitive and neuropsychological assessments of patients with pathologies affecting motor and verbal abilities, as tasks can be adapted without requiring motor (except eye movements) or verbal responses. In this review, we will examine the existing evidence of ET methods in neurodegenerative conditions and its potential clinical impact for cognitive assessment. We highlight that current evidence for ET is mostly focused on diagnostics of cognitive impairments in neurodegenerative disorders, where it is debatable whether it has any more sensitivity or specificity than existing cognitive assessments. By contrast, there is currently a lack of ET studies in more advanced disease stages, when patients' motor and verbal functions can be significantly affected, and standard cognitive assessments are challenging or often not possible. We conclude that ET is a promising method not only for cognitive diagnostics but more importantly, for potential cognitive disease tracking in progressive neurodegenerative conditions.

Saccade latencies during a preferential looking task and objective scoring of grating acuity in children with and without visual impairments

PURPOSE

We determined the latencies of orienting responses during a preferential looking task in children with normal vision and in children with visual impairments between 6 and 12 years old, and assessed the feasibility of scoring grating detection in these populations with video-based eye tracking.

METHODS

Children performed a computerized preferential looking test, while a remote eye tracker measured the children's eye movements. The stimuli consisted of a 2 × 2 grid, with three uniform grey fields and one target field consisting of a black-and-white square wave grating. The grating was presented randomly at one of the four locations. The spatial frequencies (1.05, 2.11 and 7.02 cyc/deg) were randomly interleaved, with 10 trials per spatial frequency. Three different methods were used to score the accuracy of the responses: (1) primary saccade ends on target, (1) gaze 50% of the presentation time on target, and (3) a combination of method 1 and 2 (i.e. primary saccade ends on target, and/or gaze 50% of the presentation time on target).

RESULTS

The combined scoring method was most reliable to determine whether children could resolve the gratings. Children with visual impairments had significantly lower accuracies than children with normal vision with all three scoring methods. In addition, saccade latencies decreased with age and were significantly longer (62 ± 15 ms) in children with visual impairments.

CONCLUSION

The use of eye tracking to assess grating detection with a preferential looking task in clinical populations provides valuable additional information, including objective detection measures and developmental delays in saccade latencies.

The "eyes have it," but when in development?: The importance of a developmental perspective in our understanding of behavioral memory formation and the hippocampus

Lynn Nadel has been a trailblazer in memory research for decades. In just one example, Nadel and Zola-Morgan [Infantile amnesia, In Infant memory, Springer, Boston, MA, 1984, pp. 145-172] were the first to present the provocative notion that the extended development of the hippocampus may underlie the period of infantile amnesia. In this special issue of Hippocampus to honor Lynn Nadel, we review some of his major contributions to the field of memory development, with an emphasis on his observations that behavioral memory assessments follow an uneven, yet protracted developmental course. We present data emphasizing this point from memory-related eye movements [Hannula & Ranganath, Neuron, 2009, 63(5), 592-599]. Eye tracking is a sensitive behavioral measure, allowing for an indication of memory function even without overt responses, which is seemingly ideal for the investigation of memory in early childhood or in other nonverbal populations. However, the behavioral manifestation of these eye movements follows a U-shaped trajectory-and one that must be understood before these indictors could be broadly used as a marker of memory. We examine the change in preferential looking time to target stimuli in school-aged children and adults, and compare these eye movement responses to explicit recall measures. Our findings indicate change in the nature and timing of these eye movements in older children, causing us to question how 6-month-old infants may produce eye movements that initially appear to have the same properties as those measured in adulthood. We discuss these findings in the context of our current understanding of memory development, particularly the period of infantile amnesia.

Associative binding in early childhood: Evidence from a preferential looking paradigm

Relational memory processes are responsible for forming representations that bind together the co-occurring elements of an experience. These processes provide a foundation of episodic memory, the capacity to remember specific events about one's past. In the present research, we used a visual comparison paradigm to determine whether toddlers can form memories for the relation between co-occurring items. In Experiment 1, 66 2-year-olds viewed pairs of cartoon faces (AB; CD) and did not show a significant novelty preference for the violated associations (i.e., did not look longer at AD rearranged pair than old AB pair when exposed to AD-AB). However, toddlers looked longest at the individual face (i.e., D) violating a studied pair, which appeared to be supported by visual preference for centrally located stimuli. In Experiment 2, 46 2-year-olds participated in a similar procedure, but faces violating the pair during test were located to the periphery (e.g., AB-AC). Under these conditions, toddlers looked longer at recombined pair AC. Overall, our results show that toddlers show some ability to make item-item associations but may need to overcome preferential looking biases to demonstrate this capacity. Furthermore, looking behaviors beyond overall novelty preference may be informative even when overall novelty preference is not found.

Variations in habitual sleep and relational memory in 6-month-olds

OBJECTIVES

Adequate sleep duration and good sleep quality are considered essential for development, especially during periods of major neurodevelopmental change. Still, relations between parent-reported habitual sleep and emerging cognitive abilities within the first year of life are not well studied. Here, we examined relations between habitual sleep measures and an aspect of cognitive functioning, relational memory, which emerges as early as 6 months of age, as compared to other abilities (ie, recognition memory and attentional orienting), both of which are considered to emerge earlier in development.

PARTICIPANTS

Participants were a subset of 267 healthy typically developing 6-month-olds taking part in the Growing Up in Singapore towards Healthy Outcomes cohort study.

MEASUREMENTS

Sleep duration, sleep latency, and number and duration of night awakenings were derived from the Brief Infant Sleep Questionnaire (BISQ). Short sleep was defined as <10 hours per day, categorized as "not recommended" based on the National Sleep Foundation recommendations. Associations between sleep variables and infants' performance on 2 relational memory tests (deferred imitation and relational binding) were examined independently using hierarchical (blockwise entry) linear regression. Associations between sleep and recognition memory and attentional orienting were also explored.

RESULTS

Habitual short sleepers had poorer relational memory recall in the deferred imitation task compared with 'typical' sleepers (10-18 hours per day). Shorter sleep latency was related to a greater proportion of correct responses for certain aspects of relational binding. There were no associations between sleep and recognition memory or attention.

CONCLUSIONS

Our findings suggest that habitual sleep duration and short sleep latency associate with 6-month-olds' relational memory, suggesting a preferential association with memory tasks that are sensitive to development during the second half of the first year.

Neural signatures of recognition memory in 10- to 12-month-old infants

Understanding memory mechanisms is crucial in the study of infant social and cognitive development. Here, we show that the Nc ERP component, known to reflect frequency-related attentional and/or memory processes, is a good candidate to investigate infant recognition memory. Previous paradigms have only investigated the effect of frequency during on-line stimulus presentation, but not during stimulus encoding. In this paper, we present a novel method for measuring the neural correlates of recognition memory and the 'degree' of familiarity in 10- to 12-month-old infants. During a familiarization phase, two images were presented frequently, while another two images were presented infrequently to the infants. In the test phase, the infrequent familiar, the frequent familiar, and the novel stimuli, were all presented with equal probability. We found larger Nc amplitudes following the familiar stimuli compared to the novel ones. The 'degree' of familiarity, on the other hand, did not modulate the Nc amplitude. These results can only be explained with memory-related processes, since in our paradigm the on-line presentation frequency did not vary. Furthermore, the lack of familiarization frequency effect suggests that the Nc might be a neural correlate of declarative memory.

Nutrients or nursing? Understanding how breast milk feeding affects child cognition

Purpose

To explore the associations between type of milk feeding (the “nutrients”) and mode of breast milk feeding (the “nursing”) with child cognition.

Methods

Healthy children from the GUSTO (Growing Up in Singapore Toward healthy Outcomes) cohort participated in repeated neurodevelopmental assessments between 6 and 54 months. For “nutrients”, we compared children exclusively bottle-fed according to type of milk received: formula only (n = 296) vs some/all breast milk (n = 73). For “nursing”, we included only children who were fully fed breast milk, comparing those fed directly at the breast (n = 59) vs those fed partially/completely by bottle (n = 63).

Results

Compared to infants fed formula only, those who were bottle-fed breast milk demonstrated significantly better cognitive performance on both the Bayley Scales of Infant and Toddler Development (Third Edition) at 2 years [adjusted mean difference (95% CI) 1.36 (0.32, 2.40)], and on the Kaufman Brief Intelligence Test (Second Edition) at 4.5 years [7.59 (1.20, 13.99)]. Children bottle-fed breast milk also demonstrated better gross motor skills at 2 years than those fed formula [1.60 (0.09, 3.10)]. Among infants fully fed breast milk, those fed directly at the breast scored higher on several memory tasks compared to children bottle-fed breast milk, including the deferred imitation task at 6 months [0.67 (0.02, 1.32)] and relational binding tasks at 6 [0.41 (0.07, 0.74)], 41 [0.67 (0.04, 1.29)] and 54 [0.12 (0.01, 0.22)] months.

Conclusions

Our findings suggest that nutrients in breast milk may improve general child cognition, while nursing infants directly at the breast may influence memory.

Electronic supplementary material

The online version of this article (10.1007/s00394-019-01929-2) contains supplementary material, which is available to authorized users.

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.

The potential of eye-tracking as a sensitive measure of behavioural change in response to intervention

One challenge to the development of effective interventions to support learning and behavioural change in neurodevelopmental disorders is a lack of suitable outcome measures. Eye-tracking has been used widely to chart cognitive development and clinically-relevant group differences in many populations. This proof-of-concept study investigates whether it also has the potential to act as a marker of treatment effects, by testing its sensitivity to differential change over a short period of exposure to an iPad app in typically developing children. The app targets a key skill in early social communication development, by rewarding attention to people, operationalised via a finger-tap on screen. We measured attention to images taken from the app, and a selection of matched stimuli to test generalisation of effects, at baseline and two weeks later. Children were assigned to either an app-exposure or no-app condition in the intervening period. The app exposure group showed increases in fixation on people for images from the app, and for distant-generalisation photographs, at high levels of complexity. We conclude that, with careful selection of stimuli, eye-tracking has the potential to make a valuable contribution to the range of outcome measures available for psycho-behavioural interventions in neurodevelopmental disorders.

Small Sets of Novel Words Are Fully Retained After 1-Week in Typically Developing Children and Down Syndrome: A Fast Mapping Study

OBJECTIVES

Down syndrome (DS) is a population with known hippocampal impairment, with studies showing that individuals with DS display difficulties in spatial navigation and remembering arbitrary bindings. Recent research has also demonstrated the importance of the hippocampus for novel word-learning. Based on these data, we aimed to determine whether individuals with DS show deficits in learning new labels and if they may benefit from encoding conditions thought to be less reliant on hippocampal function (i.e., through fast mapping).

METHODS

In the current study, we examined immediate, 5-min, and 1-week delayed word-learning across two learning conditions (e.g., explicit encoding vs. fast mapping). These conditions were examined across groups (twenty-six 3- to 5-year-old typically developing children and twenty-six 11- to 28-year-old individuals with DS with comparable verbal and nonverbal scores on the Kaufman Brief Intelligence Test - second edition) and in reference to sleep quality.

RESULTS

Both individuals with and without DS showed retention after a 1-week delay, and the current study found no benefit of the fast mapping condition in either group contrary to our expectations. Eye tracking data showed that preferential eye movements to target words were not present immediately but emerged after 1-week in both groups. Furthermore, sleep measures collected via actigraphy did not relate to retention in either group.

CONCLUSIONS

This study presents novel data on long-term knowledge retention in reference to sleep patterns in DS and adds to a body of knowledge helping us to understand the processes of word-learning in typical and atypically developing populations. (JINS, 2018, 24, 955-965).

Word Processing in Scene Context: An Event-Related Potential Study in Young Children

Semantic priming has been demonstrated in object or word contexts in toddlers. However, less is known about semantic priming in scene context. In this study, 24-month-olds with high and low vocabulary skills were presented with visual scenes (e.g., kitchen) followed by semantically consistent (e.g., spoon) or inconsistent (e.g., bed) spoken words. Inconsistent scene-word pairs evoked a larger N400 component over the frontal areas. Low-producers presented a larger N400 over the right while high-producers over the left frontal areas. Our results suggest that contextual information facilitates word processing in young children. Additionally, children with different linguistic skills activate different neural structures.

The feasibility of automated eye tracking with the Early Childhood Vigilance Test of attention in younger HIV-exposed Ugandan children

OBJECTIVE

Tobii eye tracking was compared with webcam-based observer scoring on an animation viewing measure of attention (Early Childhood Vigilance Test; ECVT) to evaluate the feasibility of automating measurement and scoring. Outcomes from both scoring approaches were compared with the Mullen Scales of Early Learning (MSEL), Color-Object Association Test (COAT), and Behavior Rating Inventory of Executive Function for preschool children (BRIEF-P).

METHOD

A total of 44 children 44 to 65 months of age were evaluated with the ECVT, COAT, MSEL, and BRIEF-P. Tobii ×2-30 portable infrared cameras were programmed to monitor pupil direction during the ECVT 6-min animation and compared with observer-based PROCODER webcam scoring.

RESULTS

Children watched 78% of the cartoon (Tobii) compared with 67% (webcam scoring), although the 2 measures were highly correlated (r = .90, p = .001). It is possible for 2 such measures to be highly correlated even if one is consistently higher than the other (Bergemann et al., 2012). Both ECVT Tobii and webcam ECVT measures significantly correlated with COAT immediate recall (r = .37, p = .02 vs. r = .38, p = .01, respectively) and total recall (r = .33, p = .06 vs. r = .42, p = .005) measures. However, neither the Tobii eye tracking nor PROCODER webcam ECVT measures of attention correlated with MSEL composite cognitive performance or BRIEF-P global executive composite.

CONCLUSION

ECVT scoring using Tobii eye tracking is feasible with at-risk very young African children and consistent with webcam-based scoring approaches in their correspondence to one another and other neurocognitive performance-based measures. By automating measurement and scoring, eye tracking technologies can improve the efficiency and help better standardize ECVT testing of attention in younger children. This holds promise for other neurodevelopmental tests where eye movements, tracking, and gaze length can provide important behavioral markers of neuropsychological and neurodevelopmental processes associated with such tests. (PsycINFO Database Record

Beyond eye gaze: What else can eyetracking reveal about cognition and cognitive development?

This review provides an introduction to two eyetracking measures that can be used to study cognitive development and plasticity: pupil dilation and spontaneous blink rate. We begin by outlining the rich history of gaze analysis, which can reveal the current focus of attention as well as cognitive strategies. We then turn to the two lesser-utilized ocular measures. Pupil dilation is modulated by the brain's locus coeruleus-norepinephrine system, which controls physiological arousal and attention, and has been used as a measure of subjective task difficulty, mental effort, and neural gain. Spontaneous eyeblink rate correlates with levels of dopamine in the central nervous system, and can reveal processes underlying learning and goal-directed behavior. Taken together, gaze, pupil dilation, and blink rate are three non-invasive and complementary measures of cognition with high temporal resolution and well-understood neural foundations. Here we review the neural foundations of pupil dilation and blink rate, provide examples of their usage, describe analytic methods and methodological considerations, and discuss their potential for research on learning, cognitive development, and plasticity.

Bound to remember: Infants show superior memory for objects presented at event boundaries

Following Event Segmentation Theory (EST) adult memory is enhanced at event boundaries (EB). The present study set out to explore this in infancy. Sixty-eight 21-month-olds watched a cartoon with one of two objects (counterbalanced) inserted for 3s either at EB or between EB. Ten minutes later they watched both objects (familiar and novel) in a 10s Visual Paired Comparison (VPC) test while being eye-tracked. Furthermore, they were asked to point to the previous object. Based on EST, we hypothesized that objects inserted at EB would be processed more fully, resulting in improved memory compared to objects inserted between EB. Only infants with objects at EB exhibited memory evidenced by a transient familiarity preference for the first 3s of the test. Only 18 infants completed the pointing test, but all infants presented with objects at EB (10/10) pointed to the correct (familiar) object, which was not the case for the infants presented with objects between EB (5/8).

A crucial temporal accuracy test of combining EEG and Tobii eye tracker

Eye tracking and event-related potentials have been widely used in the field of cognitive psychology and neuroscience. Both techniques have the ability to refine cognitive models through a precise timeline description; nevertheless, they also have severe limitations. Combining measures of event-related potentials and eye movements can contribute to cognitive process capture, which provides the possibility to determine precisely when and in which order different cognitive operations occur. Combining of event-related potentials and eye movements has been recently conducted by synchronizing measures from an infrared eye tracker with an electroencephalograph to allow simultaneous data recording. Here, we describe in detail 4 types of co-registration methods for event-related potentials and eye movements on the Tobii platform. Moreover, the present investigation was designed to evaluate the temporal accuracy of data obtained using the 4 methods. We found that the method based on the Tobii Pro Analytics software development kit had a higher degree of temporal accuracy than the other co-registration methods. Furthermore, the reasons for the different temporal accuracies were assessed, and potential measures to correct clock drift were taken. General suggestions are made regarding timing in the co-registration of the electroencephalograph and eye tracker.

Social Models Enhance Apes' Memory for Novel Events

Nonhuman primates are more likely to learn from the actions of a social model than a non-social "ghost display", however the mechanism underlying this effect is still unknown. One possibility is that live models are more engaging, drawing increased attention to social stimuli. However, recent research with humans has suggested that live models fundamentally alter memory, not low-level attention. In the current study, we developed a novel eye-tracking paradigm to disentangle the influence of social context on attention and memory in apes. Tested in two conditions, zoo-housed apes (2 gorillas, 5 chimpanzees) were familiarized to videos of a human hand (social condition) and mechanical claw (non-social condition) constructing a three-block tower. During the memory test, subjects viewed side-by-side pictures of the previously-constructed block tower and a novel block tower. In accordance with looking-time paradigms, increased looking time to the novel block tower was used to measure event memory. Apes evidenced memory for the event featuring a social model, though not for the non-social condition. This effect was not dependent on attention differences to the videos. These findings provide the first evidence that, like humans, social stimuli increase nonhuman primates' event memory, which may aid in information transmission via social learning.

Infants Encode Phonetic Detail during Cross-Situational Word Learning

Infants often hear new words in the context of more than one candidate referent. In cross-situational word learning (XSWL), word-object mappings are determined by tracking co-occurrences of words and candidate referents across multiple learning events. Research demonstrates that infants can learn words in XSWL paradigms, suggesting that it is a viable model of real-world word learning. However, these studies have all presented infants with words that have no or minimal phonological overlap (e.g., BLICKET and GAX). Words often contain some degree of phonological overlap, and it is unknown whether infants can simultaneously encode fine phonological detail while learning words via XSWL. We tested 12-, 15-, 17-, and 20-month-olds' XSWL of eight words that, when paired, formed non-minimal pairs (MPs; e.g., BON-DEET) or MPs (e.g., BON-TON, DEET-DIT). The results demonstrated that infants are able to learn word-object mappings and encode them with sufficient phonetic detail as to identify words in both non-minimal and MP contexts. Thus, this work suggests that infants are able to simultaneously discriminate phonetic differences between words and map words to referents in an implicit learning paradigm such as XSWL.

Learning words and learning sounds: Advances in language development

Phonological development is sometimes seen as a process of learning sounds, or forming phonological categories, and then combining sounds to build words, with the evidence taken largely from studies demonstrating 'perceptual narrowing' in infant speech perception over the first year of life. In contrast, studies of early word production have long provided evidence that holistic word learning may precede the formation of phonological categories. In that account, children begin by matching their existing vocal patterns to adult words, with knowledge of the phonological system emerging from the network of related word forms. Here I review evidence from production and then consider how the implicit and explicit learning mechanisms assumed by the complementary memory systems model might be understood as reconciling the two approaches.

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.

More to it than meets the eye: how eye movements can elucidate the development of episodic memory

The ability to recognise past events along with the contexts in which they occurred is a hallmark of episodic memory, a critical capacity. Eye movements have been shown to track veridical memory for the associations between events and their contexts (relational binding). Such eye-movement effects emerge several seconds before, or in the absence of, explicit response, and are linked to the integrity and function of the hippocampus. Drawing from research from infancy through late childhood, and by comparing to investigations from typical adults, patient populations, and animal models, it seems increasingly clear that eye movements reflect item-item, item-temporal, and item-spatial associations in developmental populations. We analyse this line of work, identify missing pieces in the literature and outline future avenues of research, in order to help elucidate the development of episodic memory.

Relational Memory Is Evident in Eye Movement Behavior despite the Use of Subliminal Testing Methods

While it is generally agreed that perception can occur without awareness, there continues to be debate about the type of representational content that is accessible when awareness is minimized or eliminated. Most investigations that have addressed this issue evaluate access to well-learned representations. Far fewer studies have evaluated whether or not associations encountered just once prior to testing might also be accessed and influence behavior. Here, eye movements were used to examine whether or not memory for studied relationships is evident following the presentation of subliminal cues. Participants assigned to experimental or control groups studied scene-face pairs and test trials evaluated implicit and explicit memory for these pairs. Each test trial began with a subliminal scene cue, followed by three visible studied faces. For experimental group participants, one face was the studied associate of the scene (implicit test); for controls none were a match. Subsequently, the display containing a match was presented to both groups, but now it was preceded by a visible scene cue (explicit test). Eye movements were recorded and recognition memory responses were made. Participants in the experimental group looked disproportionately at matching faces on implicit test trials and participants from both groups looked disproportionately at matching faces on explicit test trials, even when that face had not been successfully identified as the associate. Critically, implicit memory-based viewing effects seemed not to depend on residual awareness of subliminal scene cues, as subjective and objective measures indicated that scenes were successfully masked from view. The reported outcomes indicate that memory for studied relationships can be expressed in eye movement behavior without awareness.

A new system for quantitative evaluation of infant gaze capabilities in a wide visual field

BACKGROUND

The visual assessment of infants poses specific challenges: many techniques that are used on adults are based on the patient's response, and are not suitable for infants. Significant advances in the eye-tracking have made this assessment of infant visual capabilities easier, however, eye-tracking still requires the subject's collaboration, in most cases and thus limiting the application in infant research. Moreover, there is a lack of transferability to clinical practice, and thus it emerges the need for a new tool to measure the paradigms and explore the most common visual competences in a wide visual field. This work presents the design, development and preliminary testing of a new system for measuring infant's gaze in the wide visual field called CareToy C: CareToy for Clinics.

METHODS

The system is based on a commercial eye tracker (SmartEye) with six cameras running at 60 Hz, suitable for measuring an infant's gaze. In order to stimulate the infant visually and audibly, a mechanical structure has been designed to support five speakers and five screens at a specific distance (60 cm) and angle: one in the centre, two on the right-hand side and two on the left (at 30° and 60° respectively). Different tasks have been designed in order to evaluate the system capability to assess the infant's gaze movements during different conditions (such as gap, overlap or audio-visual paradigms). Nine healthy infants aged 4-10 months were assessed as they performed the visual tasks at random.

RESULTS

We developed a system able to measure infant's gaze in a wide visual field covering a total visual range of ±60° from the centre with an intermediate evaluation at ±30°. Moreover, the same system, thanks to different integrated software, was able to provide different visual paradigms (as gap, overlap and audio-visual) assessing and comparing different visual and multisensory sub-competencies. The proposed system endowed the integration of a commercial eye-tracker into a purposive setup in a smart and innovative way.

CONCLUSIONS

The proposed system is suitable for measuring and evaluating infant's gaze capabilities in a wide visual field, in order to provide quantitative data that can enrich the clinical assessment.

Building metamemorial knowledge over time: insights from eye tracking about the bases of feeling-of-knowing and confidence judgments

Metamemory processes depend on different factors across the learning and memory time-scale. In the laboratory, subjects are often asked to make prospective feeling-of-knowing (FOK) judgments about target retrievability, or are asked to make retrospective confidence judgments (RCJs) about the retrieved target. We examined distinct and shared contributors to metamemory judgments, and how they were built over time. Eye movements were monitored during a face-scene associative memory task. At test, participants viewed a studied scene, then rated their FOK that they would remember the associated face. This was followed by a forced choice recognition test and RCJs. FOK judgments were less accurate than RCJ judgments, showing that the addition of mnemonic experience can increase metacognitive accuracy over time. However, there was also evidence that the given FOK rating influenced RCJs. Turning to eye movements, initial analyses showed that higher cue fluency was related to both higher FOKs and higher RCJs. However, further analyses revealed that the effects of the scene cue on RCJs were mediated by FOKs. Turning to the target, increased viewing time and faster viewing of the correct associate related to higher FOKs, consistent with the idea that target accessibility is a basis of FOKs. In contrast, the amount of viewing directed to the chosen face, regardless of whether it was correct, predicted higher RCJs, suggesting that choice experience is a significant contributor RCJs. We also examined covariates of the change in RCJ rating from the FOK rating, and showed that increased and faster viewing of the chosen face predicted raising one's confidence above one's FOK. Taken together these results suggest that metamemory judgments should not be thought of only as distinct subjective experiences, but complex processes that interact and evolve as new psychological bases for subjective experience become available.

Episodic memory and future thinking during early childhood: Linking the past and future

Despite extensive examination of episodic memory and future thinking development, little is known about the concurrent emergence of these capacities during early childhood. In Experiment 1, 3-year-olds participated in an episodic memory hiding task ("what, when, where" [WWW] components) with an episodic future thinking component. In Experiment 2, a group of 4-year-olds (including children from Experiment 1) participated in the same task (different objects and locations), providing the first longitudinal investigation of episodic memory and future thinking. Although children exhibited age-related improvements in recall, recognition, and binding of the WWW episodic memory components, there were no age-related changes in episodic future thinking. At both ages, WWW episodic memory performance was higher than future thinking performance, and episodic future thinking and WWW memory components were unrelated. These findings suggest that the WWW components of episodic memory are potentially less fragile than the future components when assessed in a cognitively demanding task.

Eye movements provide an index of veridical memory for temporal order

The present research examined whether eye movements during retrieval capture the relation between an event and its temporal attributes. In two experiments (N=76), we found converging evidence that eye movements reflected the veridicality of memory for temporal order seconds before overt memory judgments, suggesting that these movements captured indirect access to temporal information. These eye movements did not entirely depend on the amount of contextual cueing available (Experiment 1) and reflected the unique ordinal position of an event in a sequence (Experiment 2). Based on our results, we conclude that eye movements reflected the absolute temporal order of past events.

Do semantic contextual cues facilitate transfer learning from video in toddlers?

Young children typically demonstrate a transfer deficit, learning less from video than live presentations. Semantically meaningful context has been demonstrated to enhance learning in young children. We examined the effect of a semantically meaningful context on toddlers’ imitation performance. Two- and 2.5-year-olds participated in a puzzle imitation task to examine learning from either a live or televised model. The model demonstrated how to assemble a three-piece puzzle to make a fish or a boat, with the puzzle demonstration occurring against a semantically meaningful background context (ocean) or a yellow background (no context). Participants in the video condition performed significantly worse than participants in the live condition, demonstrating the typical transfer deficit effect. While the context helped improve overall levels of imitation, especially for the boat puzzle, only individual differences in the ability to self-generate a stimulus label were associated with a reduction in the transfer deficit.

Memory for complex visual objects but not for allocentric locations during the first year of life

Although human infants demonstrate early competence to retain visual information, memory capacities during infancy remain largely undocumented. In three experiments, we used a Visual Paired Comparison (VPC) task to examine abilities to encode identity (Experiment 1) and spatial properties (Experiments 2a and 2b) of unfamiliar complex visual patterns during the first year of life. In the first experiment, 6- and 9-month-old infants were familiarized with visual arrays composed of four abstract patterns arranged in a square configuration. Recognition memory was evaluated by presenting infants with the familiarized array paired with a novel array composed of four new patterns. The second couple of experiments aimed to examine infant ability to encode the spatial relationships between each pattern of the array (e.g., where is A in the square configuration). The 6-, 9- and 12-month-old infants were tested on a spatial version of the VPC task, in which the novel array was composed of the same patterns than the familiarized array but arranged differently within the square configuration. Results indicated that infants retained the identity of the patterns but not their specific spatial relationships within the square configuration (i.e., allocentric location of the patterns), suggesting either an immaturity of the processes involved in object-to-location binding, or the inappropriateness of unfamiliar complex objects to reveal such early allocentric abilities.

20 years after “The ontogeny of human memory: A cognitive neuroscience perspective,” where are we?

In 1995, Nelson published a paper describing a model of memory development during the first years of life. The current article seeks to provide an update on the original work published 20 years ago. Specifically, we review our current knowledge on the relation between the emergence of explicit memory functions throughout development and the maturation of associated brain regions. It is now well established that the brain regions subserving explicit memory functions (i.e. the hippocampal formation) are far from mature at birth, and exhibit important and gradual structural changes during childhood and beyond. Accordingly, explicit memory functions develop progressively. While some functions are present shortly after birth (formerly proposed as pre-explicit memory), others exhibit protracted developmental profiles during the first years of life. We examine the link between the emergence of different memory functions and the maturation of specific hippocampal circuits.

Infant feeding effects on early neurocognitive development in Asian children

BACKGROUND

Breastfeeding has been shown to enhance global measures of intelligence in children. However, few studies have examined associations between breastfeeding and specific cognitive task performance in the first 2 y of life, particularly in an Asian population.

OBJECTIVE

We assessed associations between early infant feeding and detailed measures of cognitive development in the first 2 y of life in healthy Asian children born at term.

DESIGN

In a prospective cohort study, neurocognitive testing was performed in 408 healthy children (aged 6, 18, and 24 mo) from uncomplicated pregnancies (i.e., birth weight >2500 and <4000 g, gestational age ≥37 wk, and 5-min Apgar score ≥9). Tests included memory (deferred imitation, relational binding, habituation) and attention tasks (visual expectation, auditory oddball) as well as the Bayley Scales of Infant and Toddler Development, Third Edition (BSID-III). Children were stratified into 3 groups (low, intermediate, and high) on the basis of breastfeeding duration and exclusivity.

RESULTS

After potential confounding variables were controlled for, significant associations and dose-response relations were observed for 4 of the 15 tests. Higher breastfeeding exposure was associated with better memory at 6 mo, demonstrated by greater preferential looking toward correctly matched items during early portions of a relational memory task (i.e., relational binding task: P-trend = 0.015 and 0.050 for the first two 1000-ms time bins, respectively). No effects of breastfeeding were observed at 18 mo. At 24 mo, breastfed children were more likely to display sequential memory during a deferred imitation memory task (P-trend = 0.048), and toddlers with more exposure to breastfeeding scored higher in receptive language [+0.93 (0.23, 1.63) and +1.08 (0.10, 2.07) for intermediate- and high-breastfeeding groups, respectively, compared with the low-breastfeeding group], as well as expressive language [+0.58 (-0.06, 1.23) and +1.22 (0.32, 2.12) for intermediate- and high-breastfeeding groups, respectively] assessed via the BSID-III.

CONCLUSIONS

Our findings suggest small but significant benefits of breastfeeding for some aspects of memory and language development in the first 2 y of life, with significant improvements in only 4 of 15 indicators. Whether the implicated processes confer developmental advantages is unknown and represents an important area for future research. This trial was registered at www.clinicaltrials.gov as NCT01174875.