What Do Infants Remember When They Forget? Location and Identity in 6-Month-Olds’ Memory for Objects

The development of visual cognition: The emergence of spatial congruency bias

In adults, spatial location plays a special role in visual object processing. People are more likely to judge two sequentially presented objects as being identical when they appear in the same location compared to in different locations (a phenomenon referred to as Spatial Congruency Bias [SCB]). However, no comparable Identity Congruency Bias (ICB) is found, suggesting an asymmetric location-identity relationship in object binding. What gives rise to this asymmetric congruency bias? This paper considered two possible hypotheses. Hypothesis 1 suggests that the asymmetric congruency bias results from an inherently special role of location in the visual system. In contrast, Hypothesis 2 suggests that the asymmetric congruency bias is a product of development, reflecting people's experience with the world. To distinguish the two hypotheses, we tested both adults' and 5-year-old children's SCB and ICB by Identity Judgment Experiments and Spatial Judgment Experiments, respectively. The study found that adults only exhibited a SCB, but no ICB. However, young children exhibited both SCB and ICB, suggesting a symmetric congruency bias and reciprocal influences between location and identity in early development. The results indicate that the asymmetric location-identity relationship develops as object identity's influence on location gets pruned away, while location's influence on identity is preserved, possibly due to people's gained experiences with regularities of the world. RESEARCH HIGHLIGHTS: Adults exhibit Spatial Congruency Bias-an asymmetric location-identity relationship with location biasing their judgment of object identities, but not vice versa. Asymmetric congruency bias may result from an inherently special role of location in visual system (Hypothesis 1) or accumulated experiences with the world (Hypothesis 2). To distinguish the two hypotheses, the study investigated the Spatial Congruency Bias and Identity Congruency Bias in both adults and 5-year-old children. Unlike adults who exhibited only Spatial Congruency Bias, 5-year-old children exhibited both Spatial Congruency Bias and Identity Congruency Bias.

"Catastrophic" set size limits on infants' capacity to represent objects: A systematic review and Bayesian meta-analysis

Decades of research has revealed that humans can concurrently represent small quantities of three-dimensional objects as those objects move through space or into occlusion. For infants (but not older children or adults), this ability apparently comes with a significant limitation: when the number of occluded objects exceeds three, infants experience what has been characterized as a "catastrophic" set size limit, failing to represent even the approximate quantity of the hidden array. Infants' apparent catastrophic representational failures suggest a significant information processing limitation in the first years of life, and the evidence has been used as support for prominent theories of the development of object and numerical cognition. However, the evidence for catastrophic failure consists of individual small-n experiments that use null hypothesis significance testing to obtain null results (i.e., p > 0.05). Whether catastrophic representational failures are robust or reliable across studies, methods, and labs is not known. Here we report a systematic review and Bayesian meta-analysis to examine the strength of the evidence in favor of catastrophic representational failures in infancy. Our analysis of 22 experiments across 12 reports, with a combined total of n = 367 infants aged 10-20 months, revealed strong support for the evidence for catastrophic set size limits. A complementary analysis found moderate support for infants' success when representing fewer than four objects. We discuss the implications of our findings for theories of object and numerical cognitive development. RESEARCH HIGHLIGHTS: Previous work has suggested that infants are unable to concurrently represent four or more objects-a "catastrophic" set size limit. We reviewed this work and conducted a Bayesian meta-analysis to examine the robustness of this limit across individual small-n experiments. We found strong support for the evidence for catastrophic set size limits, and moderate support for infants' success when representing fewer than four objects.

An object's categorizability impacts whether infants encode surface features into their object representations

Infants encode the surface features of simple, unfamiliar objects (e.g., red triangle) and the categorical identities of familiar, categorizable objects (e.g., car) into their representations of these objects. We asked whether 16-18-month-olds ignore non-diagnostic surface features (e.g., color) in favor of encoding an object's categorical identity (e.g., car) when objects are from familiar categories. In Experiment 1 (n = 18), we hid a categorizable object inside an opaque box. In No Switch trials, infants retrieved the object that was hidden. In Switch trials, infants retrieved a different object: an object from a different category (Between-Category-Switch trials) or a different object from the same category (Within-Category-Switch trials). We measured infants' subsequent searching in the box. Infants' pattern of searching suggested that only infants who completed a Within-Category-Switch trial as their first Switch trial encoded objects' surface features, and an exploratory analysis suggested that infants who completed a Between-Category-Switch trial as their first Switch trial only encoded objects' categories. In Experiment 2 (n = 18), we confirmed that these results were due to objects' categorizability. These results suggest infants may tailor the way they encode categorizable objects depending on which object dimensions are perceived to be task relevant.

A principled link between object naming and representation is available to infants by seven months of age

By their first birthdays, infants represent objects flexibly as a function of not only whether but how the objects are named. Applying the same name to a set of different objects from the same category supports object categorization, with infants encoding commonalities among objects at the expense of individuating details. In contrast, applying a distinct name to each object supports individuation, with infants encoding distinct features at the expense of categorical information. Here, we consider the development of this nuanced link between naming and representation in infants' first year. Infants at 12 months (Study 1; N = 55) and 7 months (Study 2; N = 96) participated in an online recognition memory task. All infants saw the same objects, but their recognition of these objects at test varied as a function of how they had been named. At both ages, infants successfully recognized objects that had been named with distinct labels but failed to recognize these objects when they had all been named with the same, consistent label. This new evidence demonstrates that a principled link between object naming and representation is available by 7 months, early enough to support infants as they begin mapping words to meaning.

Objects in a social world: Infants' object representational capacity limits are shaped by objects' social relevance

Several decades of research have revealed consistent signature limits on infants' ability to represent objects. However, these signature representational limits were established with methods that often removed objects from their most common context. In infants' everyday lives, objects are very often social artifacts: they are the targets of agents' goal-directed actions, communications, and beliefs, and may have social content or relevance themselves. In this chapter, we explore the relationship between infants' object representational capacity limits and their processing of the social world. We review evidence that the social content and context of objects can shift infants' object representational limits. We discuss how taking the social world into account can yield more robust and ecologically valid estimates of infants' early representational capacities.

What is "Where": Physical Reasoning Informs Object Location

A central puzzle the visual system tries to solve is: "what is where?" While a great deal of research attempts to model object recognition ("what"), a comparatively smaller body of work seeks to model object location ("where"), especially in perceiving everyday objects. How do people locate an object, right now, in front of them? In three experiments collecting over 35,000 judgements on stimuli spanning different levels of realism (line drawings, real images, and crude forms), participants clicked "where" an object is, as if pointing to it. We modeled their responses with eight different methods, including both human response-based models (judgements of physical reasoning, spatial memory, free-response "click anywhere" judgements, and judgements of where people would grab the object), and image-based models (uniform distributions over the image, convex hull, saliency map, and medial axis). Physical reasoning was the best predictor of "where," performing significantly better than even spatial memory and free-response judgements. Our results offer insight into the perception of object locations while also raising interesting questions about the relationship between physical reasoning and visual perception.

The Binding Problem 2.0: Beyond Perceptual Features

The "binding problem" has been a central question in vision science for some 30 years: When encoding multiple objects or maintaining them in working memory, how are we able to represent the correspondence between a specific feature and its corresponding object correctly? In this letter we argue that the boundaries of this research program in fact extend far beyond vision, and we call for coordinated pursuit across the broader cognitive science community of this central question for cognition, which we dub "Binding Problem 2.0".

The best game in town: The reemergence of the language-of-thought hypothesis across the cognitive sciences

Mental representations remain the central posits of psychology after many decades of scrutiny. However, there is no consensus about the representational format(s) of biological cognition. This paper provides a survey of evidence from computational cognitive psychology, perceptual psychology, developmental psychology, comparative psychology, and social psychology, and concludes that one type of format that routinely crops up is the language-of-thought (LoT). We outline six core properties of LoTs: (i) discrete constituents; (ii) role-filler independence; (iii) predicate-argument structure; (iv) logical operators; (v) inferential promiscuity; and (vi) abstract content. These properties cluster together throughout cognitive science. Bayesian computational modeling, compositional features of object perception, complex infant and animal reasoning, and automatic, intuitive cognition in adults all implicate LoT-like structures. Instead of regarding LoT as a relic of the previous century, researchers in cognitive science and philosophy-of-mind must take seriously the explanatory breadth of LoT-based architectures. We grant that the mind may harbor many formats and architectures, including iconic and associative structures as well as deep-neural-network-like architectures. However, as computational/representational approaches to the mind continue to advance, classical compositional symbolic structures - that is, LoTs - only prove more flexible and well-supported over time.

Tracking what went where across toddlerhood: Feature-location bound object representations in 2- to 3-year-olds' working memory

Two experiments examined the development of the ability to encode, maintain, and update integrated representations of occluded objects' locations and featural identities in working memory across toddlerhood. Sixty-eight 28- to 40-month-old US toddlers (13 Asian or Pacific Islander, 6 Black, 48 White, 1 multiracial; 40 girls; tested between February 2015 and July 2017) tracked the locations of different color beads that were hidden simultaneously (Experiment 1) or sequentially (Experiment 2). Toddlers' ability to reliably store feature-location bound object representations in working memory varied as a function of age, memory load, and task demands. These results bridge a developmental gap between infancy and early childhood and provide new insights into sources of limitation and developmental change in children's early object representational capacities.

Proactive interference and the development of working memory

Working memory (WM), the ability to maintain information in service to a task, is characterized by its limited capacity. Several influential models attribute this limitation in a large extent to proactive interference (PI), the phenomenon that previously encoded, now-irrelevant information competes with relevant information. Here, we look back at the adult PI literature, spanning over 60 years, as well as recent results linking the ability to cope with PI to WM capacity. In early development, WM capacity is even more limited, yet an accounting for the role of PI has been lacking. Our Focus Article aims to address this through an integrative account: since PI resolution is mediated by networks involving the frontal cortex (particularly, the left inferior frontal gyrus) and the posterior parietal cortex, and since children have protracted development and less recruitment of these areas, the increase in the ability to cope with PI is a major factor underlying the increase in WM capacity in early development. Given this, we suggest that future research should focus on mechanistic studies of PI resolution in children. Finally, we note a crucial methodological implication: typical WM paradigms repeat stimuli from trial-to-trial, facilitating, inadvertently, PI and reducing performance; we may be fundamentally underestimating children's WM capacity. This article is categorized under: Psychology > Memory Neuroscience > Cognition Neuroscience > Development.

Topological change induces an interference effect in visual working memory

The “irrelevant-change distracting effect” refers to the effect of changes in irrelevant features on the performance of the target feature, which has frequently been used to study information processing in visual working memory (VWM). In the current study, we reported a novel interference effect in VWM: the topological-change interference effect (TCIE). In a series of six experiments, we examined the influence of topological and nontopological changes as irrelevant features on VWM using a color change detection paradigm. The results revealed that only topological changes, although task irrelevant, could produce a significant interference effect. In contrast, nontopological changes did not produce any evident interference effect. Moreover, the TCIE was a stable and lasting effect, regardless of changes in locations, reporting methods, particular stimulus figures, the other salient feature dimensions and delay interval times. Therefore, our results support the notion that topological invariance that defines perceptual objects plays an essential role in maintaining representations in VWM.

Acquiring verbal reference: The interplay of cognitive, linguistic, and general learning capacities

Verbal reference is the ability to use language to communicate about objects, events, or ideas, even if they are not witnessed directly, such as past events or faraway places. It rests on a three-way link between words, their referents, and mental representations of those referents. A foundational human capacity, verbal reference extends the communicative power of language beyond the here-and-now, enabling access to language-mediated learning and thus fueling cognitive development. In the current review, we consider how and when verbal reference develops. The existing literature suggests that verbal reference emerges around infants' first birthdays and becomes increasingly robust by their second. In discussing the powerful developmental advantages of acquiring verbal reference we propose that this achievement requires a dynamic interplay among infants' cognitive and language development, fueled by general learning capacities. We close by describing new research directions, aimed at advancing our understanding of how verbal reference emerges.

Nonverbal category knowledge limits the amount of information encoded in object representations: EEG evidence from 12-month-old infants

To what extent does language shape how we think about the world? Studies suggest that linguistic symbols expressing conceptual categories ('apple', 'squirrel') make us focus on categorical information (e.g. that you saw a squirrel) and disregard individual information (e.g. whether that squirrel had a long or short tail). Across two experiments with preverbal infants, we demonstrated that it is not language but nonverbal category knowledge that determines what information is packed into object representations. Twelve-month-olds (N = 48) participated in an electroencephalography (EEG) change-detection task involving objects undergoing a brief occlusion. When viewing objects from unfamiliar categories, infants detected both across- and within-category changes, as evidenced by their negative central wave (Nc) event-related potential. Conversely, when viewing objects from familiar categories, they did not respond to within-category changes, which indicates that nonverbal category knowledge interfered with the representation of individual surface features necessary to detect such changes. Furthermore, distinct patterns of γ and α oscillations between familiar and unfamiliar categories were evident before and during occlusion, suggesting that categorization had an influence on the format of recruited object representations. Thus, we show that nonverbal category knowledge has rapid and enduring effects on object representation and discuss their functional significance for generic knowledge acquisition in the absence of language.

How do the object-file and physical-reasoning systems interact? Evidence from priming effects with object arrays or novel labels

How do infants reason about simple physical events such as containment, tube, and support events? According to the two-system model, two cognitive systems, the object-file (OF) and physical-reasoning (PR) systems, work together to guide infants' responses to these events. When an event begins, the OF system sends categorical information about the objects and their arrangements to the PR system. This system then categorizes the event, assigns event roles to the objects, and taps the OF system for information about features previously identified as causally relevant for the event category selected. All of the categorical and featural information included in the event's representation is interpreted by the PR system's domain knowledge, which includes core principles such as persistence and gravity. The present research tested a novel prediction of the model: If the OF system could be primed to also send, at the beginning of an event, information about an as-yet-unidentified feature, the PR system would then interpret this information using its core principles, allowing infants to detect core violations involving the feature earlier than they normally would. We examined this prediction using two types of priming manipulations directed at the OF system, object arrays and novel labels. In six experiments, infants aged 7-13 months (N = 304) were tested using different event categories and as-yet-unidentified features (color in containment events, height in tube events, and proportional distribution in support events) as well as different tasks (violation-of-expectation and action tasks). In each case, infants who were effectively primed reasoned successfully about the as-yet-unidentified feature, sometimes as early as six months before they would typically do so. These converging results provide strong support for the two-system model and for the claim that uncovering how the OF and PR systems represent and exchange information is essential for understanding how infants respond to physical events.

Evaluating recall error in preschoolers: Category expectations influence episodic memory for color

Despite limited memory capacity, children are exceptional learners. How might children engage in meaningful learning despite limited memory systems? Past research suggests that adults integrate category knowledge and noisy episodic traces to aid recall when episodic memory is noisy or incomplete (e.g. Hemmer & Steyvers, 2009a,b). We suspect children utilize a similar process but integrate category and episodic traces in recall to a different degree. Here we conduct two experiments to empirically assess children's color category knowledge (Study 1) and recall of target hue values (Study 2). In Study 1, although children's generated hue values appear to be noisier than adults, we found no significant difference between children and adult's generated color category means (prototypes), suggesting that preschool-aged children's color categories are well established. In Study 2, we found that children's (like adult's) free recall of target hue values regressed towards color category means. We implemented three probabilistic memory models: one that combines category knowledge and specific target information (Integrative), a category only (Noisy Prototype) model, and a target only (Noisy Target) model to computationally evaluate recall performance. Consistent with previous studies with older children (Duffy, Huttenlocher, & Crawford, 2006), quantitative fits of the models to aggregate group-level data provided strong support for the Integrative process. However, at the individual subject level, a greater proportion of preschoolers' recall was better fit by a Prototype only model. Our results provide evidence that the integration of category knowledge in episodic memory comes online early and strongly. Implications for how the greater reliance on category knowledge by preschoolers relative to adults might track with developmental shifts in relational episodic memory are discussed.

Coding of featural information in visual working memory in 2.5-year-old toddlers

The number of objects that infants can remember in visual working memory (VWM) increases rapidly during the first few years of life (Kaldy & Leslie, 2005; Ross-Sheehy, Oakes, & Luck, 2003). However, less is understood about the representational format of VWM: whether storage is determined by fixed-precision memory slots, or the allocation of a limited continuous resource. In the current study, we adapted the Delayed Match Retrieval eye-tracking paradigm (Kaldy, Guillory, & Blaser, 2016), to test 2.5-year-old toddlers' ability to remember three object-location bindings when the to-be-remembered objects were all unique (Experiment 1) versus when they shared features such as color or shape (Experiment 2). 2.5-year-olds succeeded in Experiment 1, but only performed marginally better than chance in Experiment 2. Interestingly, when incorrect, participants in Experiment 2 were no more likely to select a decoy item that shared a feature with the target item. It seems that the increased similarity of to-be-remembered objects did not impair memory for the objects directly, but instead increased the likelihood of catastrophic forgetting.

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.

Two-year-olds succeed at MIT: Multiple identity tracking in 20- and 25-month-old infants

Infants' ability to remember objects and their locations emerges during the first year of life. However, not much is known about infants' ability to track objects' identities in a dynamic environment. Here, we tailored the delayed match retrieval eye-tracking paradigm to study infants' ability to track two object identities during occlusion-an infant version of multiple identity tracking (MIT). Delayed match retrieval uses virtual "cards" as stimuli that are first shown face up, exposing to-be-remembered information, and then turned face down, occluding it. Here, cards were subject to movement during the face-down occlusion period. We used complex non-nameable objects as card faces to discourage verbal rehearsal. In three experiments (N = 110), we compared infants' ability to track object identities when two previously exposed cards were static (Experiment 1), were moved into new positions along the same trajectory (Experiment 2), or were moved along different trajectories (Experiment 3) while face down. We found that 20-month-olds could remember two object identities when static; however, it was not until 25 months of age that infants could track when movement was introduced. Our results show that the ability to track multiple identities in visual working memory is present by 25 months.

Visual working memory representation as a topological defined perceptual object

The question of what the basic unit is of visual working memory remains one of the most fundamental and controversial issues. In the current study, we proposed a unique perspective based on early topological perception to describe the nature of representation in visual working memory. In a series of updating change-detection tasks, the repetition-benefit effect on color memory was not affected when items in the second memory array underwent massive changes of nontopological features from the first memory array. However, when the topological properties of an item changed, the repetition-benefit effect was destroyed, suggesting that the item was perceived as a new object impairing the original memory. Hence, our results suggest that a perceptual object defined by its topological invariance might be a unique perspective from which to describe representations of visual working memory.

Six-Month-Old Infants Predict Agents' Goal-Directed Actions on Occluded Objects

Infants can infer agents' goals after observing agents' goal-directed actions on objects and can subsequently make predictions about how agents will act on objects in the future. We investigated the representations supporting these predictions. We familiarized 6-month-old infants to an agent who preferentially reached for one of two featurally distinct objects following a cue. At test, the objects were sequentially occluded from the infant in the agent's presence. We asked whether infants could generate action predictions without visual access to the relevant objects by measuring whether infants shifted their gaze to the location of the agent's hidden goal object following the cue. We also examined what infants represented about the hidden objects by removing one of the occluders to reveal either the original hidden object or the unexpected other object and measuring infants' looking time. We found that, even without visual access to the objects, infants made predictive gazes to the location of the agent's occluded goal object, but failed to represent the features of either hidden object. These results suggest that infants make goal-based action predictions when the relevant objects in the scene are occluded, but doing so may come at the expense of maintaining representations of the objects.

Cues to individuation facilitate 6-month-old infants' visual short-term memory

Infants' ability to perform visual short-term memory (VSTM) tasks develops rapidly between 6 and 8 months. Here we tested the hypothesis that infants' VSTM performance is influenced by their ability to individuate simultaneously presented objects. We used a one-shot change detection task to ask whether 6-month-old infants (N = 47) would detect a change in the color of 1 item in a 2-item array when the stimulus context facilitated individuation of the items. In Experiment 1 the 2 items in the display differed in shape and color and in Experiment 2 the onset and offset times of the 2 items differed. In both experiments, 6-month-old infants detected a change, contrasting with previous results. Thus, young infants' encoding of information about individual items in multiple-item arrays is related to their ability to individuate those items. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Catastrophic individuation failures in infancy: A new model and predictions

Comparison of infant findings from the physical-reasoning and object-individuation literatures reveals a contradictory picture. On the one hand, physical-reasoning results indicate that young infants can use featural information to guide their actions on objects and to detect interaction violations (when objects interact in ways that are not physically possible) as well as change violations (when objects spontaneously undergo featural changes that are not physically possible). On the other hand, object-individuation results indicate that young infants typically cannot use featural information to detect individuation violations (when the number of objects revealed at the end of an event is less than the number of objects introduced during the event). In this article, we attempt to reconcile these two bodies of research. In a new model of early individuation, we propose that two systems help infants individuate objects in physical events: the object-file and physical-reasoning systems. Under certain conditions, disagreements between the systems result in catastrophic individuation failures, leading infants to hold no expectation at all about how many objects are present. We report experiments with 9- to 11-month-old infants (N = 216) that tested predictions from the model. After two objects emerged in alternation from behind a screen, infants detected no violation when the screen was lowered to reveal no object. Similarly, after two objects emerged in alternation from inside a box, which was then shaken, infants detected no violation when the box remained silent, as though empty. We end with new directions, suggested by our model, for research on early object representations. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Conceptually Rich, Perceptually Sparse: Object Representations in 6-Month-Old Infants’ Working Memory

Six-month-old infants can store representations of multiple objects in working memory but do not always remember the objects’ features (e.g., shape). Here, we asked whether infants’ object representations (a) may contain conceptual content and (b) may contain this content even if perceptual features are forgotten. We hid two conceptually distinct objects (a humanlike doll and a nonhuman ball) one at a time in two separate locations and then tested infants’ memory for the first-hidden object by revealing either the original hidden object or an unexpected other object. Using looking time, we found that infants remembered the categorical identity of the hidden object but failed to remember its perceptual identity. Our results suggest that young infants may encode conceptual category in a representation of an occluded object, even when perceptual features are lost.

Limits on composition of conceptual operations in 9-month-olds

Complex systems are often built from a relatively small set of basic features or operations that can be combined in myriad ways. We investigated the developmental origins of this compositional architecture in 9-month-old infants, extending recent work that demonstrated rudimentary compositional abilities in preschoolers. Infants viewed two separate object-occlusion events that depicted a single featurechange operation. They were then tested with a combined operation to determine whether they expected the outcome of the two feature changes, even though this combination was unfamiliar. In contrast to preschoolers, infants did not appear to predictively compose these simple feature-change operations. A second experiment demonstrated the ability of infants to track two operations when not combined. The failure to compose basic operations is consistent with limitations on object tracking and early numerical cognition (Feigenson & Yamaguchi, 2009). We suggest that these results can be unified via a general principle: infants have difficulty with multiple updates to a representation of an unobservable.

Contributions of Look Duration and Gaze Shift Patterns to Infants' Novelty Preferences

Data from 72 infants, tested using a serial paired-comparison paradigm, were analyzed to better understand infant novelty preferences. Infants between the ages of 15 and 26 weeks were tested in three studies with familiar stimuli displayed adjacent to novel stimuli on each trial. Differences in look duration, look number, and gaze shifts directed at novel versus familiar stimuli were assessed to measure their contributions to group and individual novelty preferences. Infants produced longer looks for novel stimuli in all three studies, and stimulus differences in look duration accounted for more than 50% of the variability in individual novelty preferences. Infants that produced more looks to novel rather than familiar stimuli did not produce overall novelty preferences unless they also looked longer at novel stimuli. Gaze shift patterns did not predict individual novelty preferences, and novel stimuli did not determine where infants looked. The infants' visual exploration was constrained by memories for the direction of the previous look as well as by the attention-holding features of novel stimuli.

Working Memory Maturation: Can We Get at the Essence of Cognitive Growth?

The theoretical and practical understanding of cognitive development depends on working memory, the limited information temporarily accessible for such daily activities as language processing and problem solving. In this article, I assess many possible reasons that working memory performance improves with development. A first glance at the literature leads to the weird impression that working memory capacity reaches adult levels during infancy but then regresses during childhood. In place of that unlikely explanation, I consider how infant studies may lead to overestimates of capacity if one neglects supports that the tasks provide, compared with adult-level tasks. Further development of working memory during the school years is also considered. Many investigators have come to suspect that working memory capacity may be constant after infancy because of various factors such as developmental increases in knowledge, filtering out of irrelevant distractions, encoding and rehearsal strategies, and pattern formation. With each of these factors controlled, though, working memory still improves during the school years. Suggestions are made for research to bridge the gap between infant and child developmental research, to understand the focus and control of attention in working memory and how these skills develop, and to pinpoint the nature of capacity and its development from infancy forward.

Delayed Match Retrieval: a novel anticipation-based visual working memory paradigm

We tested 8- and 10-month-old infants' visual working memory (VWM) for object-location bindings - what is where - with a novel paradigm, Delayed Match Retrieval, that measured infants' anticipatory gaze responses (using a Tobii T120 eye tracker). In an inversion of Delayed-Match-to-Sample tasks and with inspiration from the game Memory, in test trials, three face-down virtual 'cards' were presented. Two flipped over sequentially (revealing, e.g. a swirl pattern and then a star), and then flipped back face-down. Next, the third card was flipped to reveal a match (e.g. a star) to one of the previously seen, now face-down cards. If infants looked to the location where the (now face-down) matching card had been shown, this was coded as a correct response. To encourage anticipatory looks, infants subsequently received a reward (a brief, engaging animation) presented at that location. Ten-month-old infants performed significantly above chance, showing that their VWM could hold object-location information for the two cards. Overall, 8-month-olds' performance was at chance, but they showed a robust learning trend. These results corroborate previous findings (Kaldy & Leslie, 2005; Oakes, Ross-Sheehy & Luck, 2006) and point to rapid development of VWM for object-location bindings. However, compared to previous paradigms that measure passive gaze responses to novelty, this paradigm presents a more challenging, ecologically relevant test of VWM, as it measures the ability to make online predictions and actively localize objects based on VWM. In addition, this paradigm can be readily scaled up to test toddlers or older children without significant modification.

Statistical treatment of looking-time data

Looking times (LTs) are frequently measured in empirical research on infant cognition. We analyzed the statistical distribution of LTs across participants to develop recommendations for their treatment in infancy research. Our analyses focused on a common within-subject experimental design, in which longer looking to novel or unexpected stimuli is predicted. We analyzed data from 2 sources: an in-house set of LTs that included data from individual participants (47 experiments, 1,584 observations), and a representative set of published articles reporting group-level LT statistics (149 experiments from 33 articles). We established that LTs are log-normally distributed across participants, and therefore, should always be log-transformed before parametric statistical analyses. We estimated the typical size of significant effects in LT studies, which allowed us to make recommendations about setting sample sizes. We show how our estimate of the distribution of effect sizes of LT studies can be used to design experiments to be analyzed by Bayesian statistics, where the experimenter is required to determine in advance the predicted effect size rather than the sample size. We demonstrate the robustness of this method in both sets of LT experiments.

Infants' Understanding of Object-Directed Action: An Interdisciplinary Synthesis

Recognizing that the object-directed actions of others are governed by goals and intentions is a crucial component of human interaction. These actions often occur rapidly and without explanation, yet we learn from and predict the actions of others with remarkable speed and accuracy, even during the first year of life. This review paper will serve as a bridge between several disparate literatures that, we suggest, can each contribute to our understanding of how infants interpret action. Specifically, we provide a review not just of research on infant goal attribution per se, but also incorporate findings from studies on the mirror neuron system and infant object cognition. The integration of these various research approaches allows for a novel construal of the extents and limits of early goal attribution – one in which the importance of the entire action context is considered – and points to specific future research directions.

Varieties of Visual Working Memory Representation in Infancy and Beyond

Research on the developmental origins of visual working memory in infants has largely progressed along two separate branches. One branch is rooted in the classic work on adult visual working memory, while the other is rooted in the classic work on the object concept in infancy. Both lines of research have yielded some converging results but also some surprisingly different patterns. In this review, I show that these different patterns are evidence for two distinct types of representations, which I term feature-based and object-based. I then show that there is evidence for both representation types beyond infancy.

Infants use temporal regularities to chunk objects in memory

Infants, like adults, can maintain only a few items in working memory, but can overcome this limit by creating more efficient representations, or "chunks." Previous research shows that infants can form chunks using shared features or spatial proximity between objects. Here we asked whether infants also can create chunked representations using regularities that unfold over time. Thirteen-month old infants first were familiarized with four objects of different shapes and colors, presented in successive pairs. For some infants, the identities of objects in each pair varied randomly across familiarization (Experiment 1). For others, the objects within a pair always co-occurred, either in consistent relative spatial positions (Experiment 2a) or varying spatial positions (Experiment 2b). Following familiarization, infants saw all four objects hidden behind a screen and then saw the screen lifted to reveal either four objects or only three. Infants in Experiment 1, who had been familiarized with random object pairings, failed to look longer at the unexpected 3-object outcome; they showed the same inability to concurrently represent four objects as in other studies of infant working memory. In contrast, infants in Experiments 2a and 2b, who had been familiarized with regularly co-occurring pairs, looked longer at the unexpected outcome. These infants apparently used the co-occurrence between individual objects during familiarization to form chunked representations that were later deployed to track the objects as they were hidden at test. In Experiment 3, we confirmed that the familiarization affected infants' ability to remember the occluded objects rather than merely establishing longer-term memory for object pairs. Following familiarization to consistent pairs, infants who were not shown a hiding event (but merely saw the same test outcomes as in Experiments 2a and b) showed no preference for arrays of three versus four objects. Finally, in Experiments 4 and 5, we asked whether infants also remembered the specific identities of the objects in each chunk. In Experiment 4, we confirmed that infants remembered objects' identities in smaller arrays that did not require chunking. Next, in Experiment 5, we asked whether infants also remembered objects' identities in larger arrays that had been chunked on the basis of temporal regularities. Following a familiarization phase identical to that in Experiment 2a, we hid all four objects and then revealed either these same four objects, or four objects of which two had unexpectedly changed shape and color. Surprisingly, infants failed to look longer at the identity change outcome. Taken together, our results suggest that infants can use temporal regularities between objects to increase memory for objects' existence, but not necessarily for objects' identities.

Array heterogeneity prevents catastrophic forgetting in infants

Working memory is limited in adults and infants. But unlike adults, infants whose working memory capacity is exceeded often fail in a particularly striking way: they do not represent any of the presented objects, rather than simply remembering as many objects as they can and ignoring anything further (Feigenson & Carey, 2003, 2005). Here we explored the nature of this "catastrophic forgetting," asking whether stimuli themselves modulate the way in which infants' memory fails. We showed 13-month old infants object arrays that either were within or that exceeded working memory capacity--but, unlike previous experiments, presented objects with contrasting features. Although previous studies have repeatedly documented infants' failure to represent four identical hidden objects, in Experiments 1 and 2 we found that infants who saw four contrasting objects hidden, and then retrieved just two of the four, successfully continued searching for the missing objects. Perceptual contrast between objects sufficed to drive this success; infants succeeded regardless of whether the different objects were contrastively labeled, and regardless of whether the objects were semantically familiar or completely novel. In Experiment 3 we explored the nature of this surprising success, asking whether array heterogeneity actually expanded infants' working memory capacity or rather prevented catastrophic forgetting. We found that infants successfully continued searching after seeing four contrasting objects hidden and retrieving two of them, but not after retrieving three of them. This suggests that, like adults, infants were able to remember up to, but not beyond, the limits of their working memory capacity when representing heterogeneous arrays.

Developmental changes in visual short-term memory in infancy: evidence from eye-tracking

We assessed visual short-term memory (VSTM) for color in 6- and 8-month-old infants (n = 76) using a one-shot change detection task. In this task, a sample array of two colored squares was visible for 517 ms, followed by a 317-ms retention period and then a 3000-ms test array consisting of one unchanged item and one item in a new color. We tracked gaze at 60 Hz while infants looked at the changed and unchanged items during test. When the two sample items were different colors (Experiment 1), 8-month-old infants exhibited a preference for the changed item, indicating memory for the colors, but 6-month-olds exhibited no evidence of memory. When the two sample items were the same color and did not need to be encoded as separate objects (Experiment 2), 6-month-old infants demonstrated memory. These results show that infants can encode information in VSTM in a single, brief exposure that simulates the timing of a single fixation period in natural scene viewing, and they reveal rapid developmental changes between 6 and 8 months in the ability to store individuated items in VSTM.

Visual short-term memory for complex objects in 6- and 8-month-old infants

Infants' visual short-term memory (VSTM) for simple objects undergoes dramatic development: Six-month-old infants can store in VSTM information about only a simple object presented in isolation, whereas 8-month-old infants can store information about simple objects presented in multiple-item arrays. This study extended this work to examine the development of infants' VSTM for complex objects during this same period (N = 105). Using the simultaneous streams change detection paradigm, Experiment 1 confirmed the previous developmental trajectory between 6 and 8 months. Experiment 2 showed that doubling the exposure time did not enhance 6-month-old infants' change detection, demonstrating that the developmental change is not due to encoding speed. Thus, VSTM for simple and complex objects appears to follow the same developmental trajectory.

Factors influencing infants' ability to update object representations in memory

Remembering persisting objects over occlusion is critical to representing a stable environment. Infants remember hidden objects at multiple locations and can update their representation of a hidden array when an object is added or subtracted. However, the factors influencing these updating abilities have received little systematic exploration. Here we examined the flexibility of infants' ability to update object representations. We tested 11-month-olds in a looking-time task in which objects were added to or subtracted from two hidden arrays. Across five experiments, infants successfully updated their representations of hidden arrays when the updating occurred successively at one array before beginning at the other. But when updating required alternating between two arrays, infants failed. However, simply connecting the two arrays with a thin strip of foam-core led infants to succeed. Our results suggest that infants' construal of an event strongly affects their ability to update memory representations of hidden objects. When construing an event as containing multiple updates to the same array, infants succeed, but when construing the event as requiring the revisiting and updating of previously attended arrays, infants fail.

What's the object of object working memory in infancy? Unraveling 'what' and 'how many'

Infants have a bandwidth-limited object working memory (WM) that can both individuate and identify objects in a scene, (answering 'how many?' or 'what?', respectively). Studies of infants' WM for objects have typically looked for limits on either 'how many' or 'what', yielding different estimates of infant capacity. Infants can keep track of about three individuals (regardless of identity), but appear to be much more limited in the number of specific identities they can recall. Why are the limits on 'how many' and 'what' different? Are the limits entirely separate, do they interact, or are they simply two different aspects of the same underlying limit? We sought to unravel these limits in a series of experiments which tested 9- and 12-month-olds' WM for object identities under varying degrees of difficulty. In a violation-of-expectation looking-time task, we hid objects one at a time behind separate screens, and then probed infants' WM for the shape identity of the penultimate object in the sequence. We manipulated the difficulty of the task by varying both the number of objects in hiding locations and the number of means by which infants could detect a shape change to the probed object. We found that 9-month-olds' WM for identities was limited by the number of hiding locations: when the probed object was one of two objects hidden (one in each of two locations), 9-month-olds succeeded, and they did so even though they were given only one means to detect the change. However, when the probed object was one of three objects hidden (one in each of three locations), they failed, even when they were given two means to detect the shape change. Twelve-month-olds, by contrast, succeeded at the most difficult task level. Results show that WM for 'how many' and for 'what' are not entirely separate. Individuated objects are tracked relatively cheaply. Maintaining bindings between indexed objects and identifying featural information incurs a greater attentional/memory cost. This cost reduces with development. We conclude that infant WM supports a small number of featureless object representations that index the current locations of objects. These can have featural information bound to them, but only at substantial cost.

Seven-month-old infants chunk items in memory

Although working memory has a highly constrained capacity limit of three or four items, both adults and toddlers can increase the total amount of stored information by "chunking" object representations in memory. To examine the developmental origins of chunking, we used a violation-of-expectation procedure to ask whether 7-month-old infants, whose working memory capacity is still maturing, also can chunk items in memory. In Experiment 1, we found that in the absence of chunking cues, infants failed to remember three identical hidden objects. In Experiments 2 and 3, we found that infants successfully remembered three hidden objects when provided with overlapping spatial and featural chunking cues. In Experiment 4, we found that infants did not chunk when provided with either spatial or featural chunking cues alone. Finally, in Experiment 5, we found that infants also failed to chunk when spatial and featural cues specified different chunks (i.e., were pitted against each other). Taken together, these results suggest that chunking is available before working memory capacity has matured but still may undergo important development over the first year of life.