Development of Subordinate-Level Categorization in 3- to 7-Month-Old Infants

When Time Shifts the Boundaries: Isolating the Role of Forgetting in Children's Changing Category Representations

In studies of children's categorization, researchers have typically studied how encoding characteristics of exemplars contribute to children's generalization. However, it is unclear whether children's internal cognitive processes alone, independent of new information, may also influence their generalization. Thus, we examined the role that one cognitive process, forgetting, plays in shaping children's category representations by conducting three experiments. In the first two experiments, participants (NExp1=37, Mage=4.02 years; NExp2=32, Mage=4.48 years) saw a novel object labeled by the experimenter and then saw five new objects with between one and five features changed from the learned exemplar. The experimenter asked whether each object was a member of the same category as the exemplar; children saw the five new objects either immediately or after a five-minute delay. Children endorsed category membership at higher rates at immediate test than at delayed test, suggesting that children's category representations became narrower over time. In Experiment 3, we investigated forgetting as a key mechanism underlying the narrowing found in Experiments 1 and 2. We showed participants (NExp3=34, Mage=4.20 years) the same exemplars used in Experiments 1 and 2; then, either immediately or after a five-minute delay, we showed children seven individual object features and asked if each one had been part of the exemplar. Children's accuracy was lower after the delay, showing that they did indeed forget individual features. Taken together, these results show that forgetting plays an important role in changing children's newly-learned categories over time.

Convolutional neural networks trained with a developmental sequence of blurry to clear images reveal core differences between face and object processing

Although convolutional neural networks (CNNs) provide a promising model for understanding human vision, most CNNs lack robustness to challenging viewing conditions, such as image blur, whereas human vision is much more reliable. Might robustness to blur be attributable to vision during infancy, given that acuity is initially poor but improves considerably over the first several months of life? Here, we evaluated the potential consequences of such early experiences by training CNN models on face and object recognition tasks while gradually reducing the amount of blur applied to the training images. For CNNs trained on blurry to clear faces, we observed sustained robustness to blur, consistent with a recent report by Vogelsang and colleagues (2018). By contrast, CNNs trained with blurry to clear objects failed to retain robustness to blur. Further analyses revealed that the spatial frequency tuning of the two CNNs was profoundly different. The blurry to clear face-trained network successfully retained a preference for low spatial frequencies, whereas the blurry to clear object-trained CNN exhibited a progressive shift toward higher spatial frequencies. Our findings provide novel computational evidence showing how face recognition, unlike object recognition, allows for more holistic processing. Moreover, our results suggest that blurry vision during infancy is insufficient to account for the robustness of adult vision to blurry objects.

Labels and object categorization in six- and nine-month-olds: tracking labels across varying carrier phrases

Language shapes object categorization in infants. This starts as a general enhanced attentional effect of language, which narrows to a specific link between labels and categories by twelve months. The current experiments examined this narrowing effect by investigating when infants track a consistent label across varied input. Six-month-old infants (N = 48) were familiarized to category exemplars, each presented with the exact same labeling phrase or the same label in different phrases. Evidence of object categorization at test was only found with the same phrase, suggesting that infants were not tracking the label's consistency, but rather that of the entire input. Nine-month-olds (N = 24) did show evidence of categorization across the varied phrases, suggesting that they were tracking the consistent label across the varied input.

Integration of thought and action continued: Scale errors and categorization in toddlers

To further explore the effect of weighted arms on toddler's performance in problem solving (Arterberry et al., 2018, Infancy, 23(2), 173), the present study explored scale errors and categorization, two instances where infants appear to show more advanced knowledge than toddlers. Experiment 1 (N = 67) used a novel task for inducing scale errors among 24- to 29-month-olds. Results replicated rates of scale errors found in previous research that used different tasks. Experiment 2 used sequential touching (N = 31) and sorting measures (N = 23) to test categorization in 24-month-old children. In both measures, children showed categorization at the basic level when there was high contrast between the exemplars, but not at a basic level with low contrast or a subordinate level. In Experiments 1 and 2, half the participants were tested while wearing weighted wristbands. Weighting the arms did not affect error rates, in contrast to previous research showing that weights improved performance in search tasks. The findings are discussed in light of children's difficulty in integrating perception, cognition, and action.

The development of categorisation and conceptual thinking in early childhood: methods and limitations

We present a systematic and qualitative review of academic literature on early conceptual development (0–24 months of age), with an emphasis on methodological aspects. The final sample of our review included 281 studies reported in 115 articles. The main aims of the article were four: first, to organise studies into sets according to methodological similarities and differences; second, to elaborate on the methodological procedures that characterise each set; third, to circumscribe the empirical indicators that different sets of studies consider as proof of the existence of concepts in early childhood; last, to identify methodological limitations and to propose possible ways to overcome them. We grouped the studies into five sets: preference and habituation experiments, category extension tasks, object sorting tasks, sequential touching tasks and object examination tasks. In the “Results” section, we review the core features of each set of studies. In the “Discussion” and “Conclusions” sections, we describe, for one thing, the most relevant methodological shortcomings. We end by arguing that a situated, semiotic and pragmatic perspective that emphasises the importance of ecological validity could open up new avenues of research to better understand the development of concepts in early childhood.

Beyond perceptual development: Infant responding to social categories

A body of research is reviewed that has investigated how infants respond to social category information in faces based on differential experience. Whereas some aspects of behavioral performance (visual preference, discrimination, and scanning) are consistent with traditional models of perceptual development (induction, maintenance, and attunement), other aspects (category formation, association with valence, and selective learning) suggest the need for an account that links perceptual with social-emotional processing. We also consider how responding to social categories in infancy may anticipate subsequent responding to these categories in childhood and adulthood.

Infant categorization

In this article, we review the principal findings on infant categorization from the last 30 years. The review focuses on behaviorally based experiments with visual preference, habituation, object examining, sequential touching, and inductive generalization procedures. We propose that although this research has helped to elucidate the 'what' and 'when' of infant categorization, it has failed to clarify the mechanisms that underpin this behavior and the development of concepts. We outline a number of reasons for why the field has failed in this regard, most notably because of the context-specific nature of infant categorization and a lack of ground rules in interpreting data. We conclude by suggesting that one remedy for this issue is for infant categorization researchers to adopt more of an interdisciplinary approach by incorporating imaging and computational methods into their current methodological arsenal. WIREs Cogn Sci 2010 1 894-905 For further resources related to this article, please visit the WIREs website.

Can human eyes prevent perceptual narrowing for monkey faces in human infants?

Perceptual narrowing has been observed in human infants for monkey faces: 6-month-olds can discriminate between them, whereas older infants from 9 months of age display difficulty discriminating between them. The difficulty infants from 9 months have processing monkey faces has not been clearly identified. It could be due to the structural characteristics of monkey faces, particularly the key facial features that differ from human faces. The current study aimed to investigate whether the information conveyed by the eyes is of importance. We examined whether the presence of Caucasian human eyes in monkey faces allows recognition to be maintained in 6-month-olds and facilitates recognition in 9- and 12-month-olds. Our results revealed that the presence of human eyes in monkey faces maintains recognition for those faces at 6 months of age and partially facilitates recognition of those faces at 9 months of age, but not at 12 months of age. The findings are interpreted in the context of perceptual narrowing and suggest that the attenuation of processing of other-species faces is not reversed by the presence of human eyes.

Eye-catching odors: olfaction elicits sustained gazing to faces and eyes in 4-month-old infants

This study investigated whether an odor can affect infants' attention to visually presented objects and whether it can selectively direct visual gaze at visual targets as a function of their meaning. Four-month-old infants (n = 48) were exposed to their mother's body odors while their visual exploration was recorded with an eye-movement tracking system. Two groups of infants, who were assigned to either an odor condition or a control condition, looked at a scene composed of still pictures of faces and cars. As expected, infants looked longer at the faces than at the cars but this spontaneous preference for faces was significantly enhanced in presence of the odor. As expected also, when looking at the face, the infants looked longer at the eyes than at any other facial regions, but, again, they looked at the eyes significantly longer in the presence of the odor. Thus, 4-month-old infants are sensitive to the contextual effects of odors while looking at faces. This suggests that early social attention to faces is mediated by visual as well as non-visual cues.

Infants' Visual Recognition Memory for a Series of Categorically Related Items

We examined the interactions between visual recognition memory, working memory, and categorization by examining 6-month-old infants' (N = 168) memory for individual items in a categorized list (e.g., images of dogs or cats). In Experiments 1 and 2, infants were familiarized with 6 different cats or dogs, presented one at a time on a series of 15-s familiarization trials. When the test occurred immediately after the sixth familiarization trial (Experiment 1), infants showed strong novelty preference for items presented on the fourth or fifth familiarization trial, but not for the items presented on the first three trials or on the sixth trial. When a brief (15-s) retention delay occurred between the end of the sixth trial and the test trials (Experiment 2), memory for the sixth item was enhanced, memory for the fourth item was impaired, and memory for the fifth was unchanged relative to when no retention delay was included. Experiment 3 confirmed that infants can form a memory for the first item presented. These results reveal how factors such as interference and time to consolidate influence infants' visual recognition memory as they categorize a series of items.

Infant visual preference for fruit enhanced by congruent in-season odor

We explored the ability of infants to recognize the smell of daily foods, including strawberries and tomatoes, by using a preferential-looking-technique. Experiment 1 was conducted while strawberries were in season (from March to June) in order to enhance the frequency of participant exposure to strawberries outside of the laboratory. Thirty-seven infants aged 6-8 months were tested with a stimulus composed of a pair of photos of strawberries and tomatoes placed side by side and accompanied by a strawberry odor, a tomato odor, or no odors. Infants showed a preference for the strawberry picture when they smelled the congruent odor, but no such preference for the tomato picture. These results suggest that even young infants can recognize olfactory-visual congruency. We conducted Experiment 2 while strawberries were out of season (from July to September) to reduce participant exposure to strawberries in their daily life. Twenty-six infants aged 6-8 months were tested with a stimulus composed of a pair of photos of strawberries and tomatoes placed side by side and accompanied by a strawberry odor, or no odors. In Experiment 2, the olfactory-visual binding effect disappeared. This implies that visual-olfactory binding is triggered by an observer's experience.

Adolescents of the U.S. National Longitudinal Lesbian Family Study: sexual orientation, sexual behavior, and sexual risk exposure

This study assessed Kinsey self-ratings and lifetime sexual experiences of 17-year-olds whose lesbian mothers enrolled before these offspring were born in the longest-running, prospective study of same-sex parented families, with a 93% retention rate to date. Data for the current report were gathered through online questionnaires completed by 78 adolescent offspring (39 girls and 39 boys). The adolescents were asked if they had ever been abused and, if so, to specify by whom and the type of abuse (verbal, emotional, physical, or sexual). They were also asked to specify their sexual identity on the Kinsey scale, between exclusively heterosexual and exclusively homosexual. Lifetime sexual behavior was assessed through questions about heterosexual and same-sex contact, age of first sexual experience, contraception use, and pregnancy. The results revealed that there were no reports of physical or sexual victimization by a parent or other caregiver. Regarding sexual orientation, 18.9% of the adolescent girls and 2.7% of the adolescent boys self-rated in the bisexual spectrum, and 0% of girls and 5.4% of boys self-rated as predominantly-to-exclusively homosexual. When compared with age- and gender-matched adolescents of the National Survey of Family Growth, the study offspring were significantly older at the time of their first heterosexual contact, and the daughters of lesbian mothers were significantly more likely to have had same-sex contact. These findings suggest that adolescents reared in lesbian families are less likely than their peers to be victimized by a parent or other caregiver, and that daughters of lesbian mothers are more likely to engage in same-sex behavior and to identify as bisexual.

"What" precedes "which": developmental neural tuning in face- and place-related cortex

Although category-specific activation for faces in the ventral visual pathway appears adult-like in adolescence, recognition abilities for individual faces are still immature. We investigated how the ability to represent "individual" faces and houses develops at the neural level. Category-selective regions of interest (ROIs) for faces in the fusiform gyrus (FG) and for places in the parahippocampal place area (PPA) were identified individually in children, adolescents, and adults. Then, using an functional magnetic resonance imaging adaptation paradigm, we measured category selectivity and individual-level adaptation for faces and houses in each ROI. Only adults exhibited both category selectivity and individual-level adaptation bilaterally for faces in the FG and for houses in the PPA. Adolescents showed category selectivity bilaterally for faces in the FG and houses in the PPA. Despite this profile of category selectivity, adolescents only exhibited individual-level adaptation for houses bilaterally in the PPA and for faces in the "left" FG. Children only showed category-selective responses for houses in the PPA, and they failed to exhibit category-selective responses for faces in the FG and individual-level adaptation effects anywhere in the brain. These results indicate that category-level neural tuning develops prior to individual-level neural tuning and that face-related cortex is disproportionately slower in this developmental transition than is place-related cortex.

Looking Across Domains to Understand Infant Representation of Emotion

A comparison of the literatures on how infants represent generic object classes, gender and race information in faces, and emotional expressions reveals both common and distinctive developments in the three domains. In addition, the review indicates that some very basic questions remain to be answered regarding how infants represent facial displays of emotion, including (a) whether infants form category representations for discrete classes of emotion, when and how such representations come(b) to incorporate affective meaning, (c) the developmental trajectory for representation of emotional expression at different levels of inclusiveness (i.e., from broad to narrow or narrow to broad?), and (d) whether there is superior discrimination ability operating within more frequently experienced emotion categories.

The influence of pets on infants' processing of cat and dog images

We examined how experience at home with pets is related to infants' processing of animal stimuli in a standard laboratory procedure. We presented 6-month-old infants with photographs of cats or dogs and found that infants with pets at home (N=40) responded differently to the pictures than infants without pets (N=40). These results suggest that infants' experience in one context (at home) contributes to their processing of similar stimuli in a different context (the laboratory), and have implications for how infants' early experience shapes basic cognitive processing.

Early biases and developmental changes in self-generated object views

Object recognition depends on the seen views of objects. These views depend in part on the perceivers' own actions as they select and show object views to themselves. The self-selection of object views from manual exploration of objects during infancy and childhood may be particularly informative about the human object recognition system and its development. Here, we report for the first time on the structure of object views generated by 12 to 36 month old children (N = 54) and for comparison adults (N = 17) during manual and visual exploration of objects. Object views were recorded via a tiny video camera placed low on the participant's forehead. The findings indicate two viewing biases that grow rapidly in the first three years: a bias for planar views and for views of objects in an upright position. These biases also strongly characterize adult viewing. We discuss the implications of these findings for a developmentally complete theory of object recognition.

Categorization, categorical perception, and asymmetry in infants' representation of face race

The present study examined whether 6- and 9-month-old Caucasian infants could categorize faces according to race. In Experiment 1, infants were familiarized with different female faces from a common ethnic background (i.e. either Caucasian or Asian) and then tested with female faces from a novel race category. Nine-month-olds were able to form discrete categories of Caucasian and Asian faces. However, 6-month-olds did not form discrete categories of faces based on race. In Experiment 2, a second group of 6- and 9-month-olds was tested to determine whether they could discriminate between different faces from the same race category. Results showed that both age groups could only discriminate between different faces from the own-race category of Caucasian faces. The findings of the two experiments taken together suggest that 9-month-olds formed a category of Caucasian faces that are further differentiated at the individual level. In contrast, although they could form a category of Asian faces, they could not discriminate between such other-race faces. This asymmetry in category formation at 9 months (i.e. categorization of own-race faces vs. categorical perception of other-race faces) suggests that differential experience with own- and other-race faces plays an important role in infants' acquisition of face processing abilities.

Experience-based and on-line categorization of objects in early infancy

What processes do infants employ in categorizing? Infants might categorize on line as they encounter category-related entities; alternatively, infants might depend on prior experience with entities in formulating categories. These alternatives were tested in forty-four 5-month-olds. Infants who were familiarized in the laboratory with a category of never-before-seen objects subsequently treated novel objects of the same category as familiar-they categorized on line-just as did infants who were exposed to objects from the same category at home for 2 months leading to their laboratory assessment of object categorization. Infants with home experience also recognized novel category objects as familiar from the outset-that is, prior experience with category exemplars was brought to bear in laboratory tasks.

The development of object categorization in young children: hierarchical inclusiveness, age, perceptual attribute, and group versus individual analyses

Multiple levels of category inclusiveness in 4 object domains (animals, vehicles, fruit, and furniture) were examined using a sequential touching procedure and assessed in both individual and group analyses in eighty 12-, 18-, 24-, and 30-month-olds. The roles of stimulus discriminability and child motor development, fatigue, and actions were also investigated. More inclusive levels of categorization systematically emerged before less inclusive levels, and a consistent advantage for categorizing high versus low perceptual contrasts was found. Group and individual analyses generally converged, but individual analyses added information about child categorization over group analyses. The development of object categorization in young children is discussed in light of efficiency of processing and similarity-differentiation theories.

Developmental changes in visual object recognition between 18 and 24 months of age

Two experiments examined developmental changes in children's visual recognition of common objects during the period of 18 to 24 months. Experiment 1 examined children's ability to recognize common category instances that presented three different kinds of information: (1) richly detailed and prototypical instances that presented both local and global shape information, color, textural and featural information, (2) the same rich and prototypical shapes but no color, texture or surface featural information, or (3) that presented only abstract and global representations of object shape in terms of geometric volumes. Significant developmental differences were observed only for the abstract shape representations in terms of geometric volumes, the kind of shape representation that has been hypothesized to underlie mature object recognition. Further, these differences were strongly linked in individual children to the number of object names in their productive vocabulary. Experiment 2 replicated these results and showed further that the less advanced children's object recognition was based on the piecemeal use of individual features and parts, rather than overall shape. The results provide further evidence for significant and rapid developmental changes in object recognition during the same period children first learn object names. The implications of the results for theories of visual object recognition, the relation of object recognition to category learning, and underlying developmental processes are discussed.

Early development of perceptual expertise: within-basic-level categorization experience facilitates the formation of subordinate-level category representations in 6- to 7-month-old infants

A behavioral manifestation of perceptual expertise is the shift in recognition downward toward the subordinate level. Here, a familiarization-novelty preference procedure was used to determine whether 6- to 7-month-old infants could be induced to form category representations for cats and dogs at the subordinate level. In Experiment 1, the infants succeeded in forming subordinate-level category representations for beagle dogs and Siamese cats, but only when provided with previous experience on a subordinate-level category-formation task from within the same basic-level category (i.e., Saint Bernard dogs or tabby cats). When the prior category-formation task involved a different basic-level category, subsequent subordinate-level category learning was not in evidence. The preferences in Experiment 1 were shown in Experiments 2 and 3 not to be attributable to a priori preference or within-category discrimination failure. The findings suggest that within-basic-level categorization experience can facilitate the formation of subordinate-level category representations in the first half-year of life.

Are primary-school-aged children experts in spatial associate learning?

In two experiments (Experiment 1: N = 180, Experiment 2: N = 150), we investigated the anecdotal observation that school age children are assumed to be experts in spatial associate learning. In the first experiment, second graders, sixth graders, and adults learned the associations between 32 pictures and either a position or a word. 16 pictures had each to be associated with one position in a 4-by-4 grid of squares (spatial condition); the other 16 pictures had each to be associated to one of 16 monosyllabic words (verbal condition). After a 3 min distractor interval the associated position or word had to be retrieved with the pictures as cues. In Experiment 2, the results were replicated in principle with modifications in the experimental details. Performance improvement as a function of age turned out to be substantially larger in the verbal condition compared to the spatial one. The results are traced back to the idea that spatial associate learning is a cognitive function maturating early during life span.

Infants' Developing Appreciation of Similarities Between Model Objects and Their Real-World Referents

Previous research suggests that model competence does not emerge until relatively late in infancy (20-26 months). Development was systematically analyzed within 3 key areas--count noun learning, dual representation, and categorization-hypothesized to support the emergence of model competence in the second year. In an object-handling preferential looking task, 21- to 26-month-olds matched model objects to referents only when count noun knowledge was high. When dual representation demands were reduced through the use of pictures in place of model objects, 20-month-olds with low count noun vocabularies succeeded in relating symbols to referents. Finally, change in infants' construal of a model object as a member of a category was documented between 14 and 20 months of age.

Multidimensional shape similarity in the development of visual object classification

The current work examined age differences in the classification of novel object images that vary in continuous dimensions of structural shape. The structural dimensions employed are two that share a privileged status in the visual analysis and representation of objects: the shape of discrete prominent parts and the attachment positions of those parts. Experiment 1 involved a triad classification task in which participants at each of three different ages (5 years, 8 years, and adult) classified object images from two distinct stimulus sets. Across both sets, the youngest children demonstrated a systematic bias toward the shape of discrete parts during their judgments. With increasing age, participants increasingly came to select both the shape and the position of parts when classifying the images. The findings from Experiment 2 indicate that the local shape bias observed in young children's classifications is not merely a consequence of a discrimination advantage for that dimension. Results are discussed in relation to corresponding age-related changes in other functional contexts of visual processing.

Neural Markers of Categorization in 6-Month-Old Infants

Little is known of the neural processes that underlie concept-formation abilities in human infants. We investigated category-learning processes in infants both by using a common behavioral measure and by recording the brain's electrical activity (event-related potentials, or ERPs). ERPs were recorded while 6-month-olds viewed cat images during training, followed by novel cat images interspersed with novel dog images during test. The data indicate that distinct neural signals correspond with learning of a category presented during familiarization, preferential responding to a novel category, and representation of category exemplars at multiple levels of inclusiveness. The results suggest that fundamental components of the neural architecture supporting object categorization are functional within the first half-year of postnatal life, before infants acquire language and young children engage in formal learning of semantic categories. The findings are discussed in terms of their implications for models of category learning and development.

Beyond the distributional input? A developmental investigation of asymmetry in infants' categorization of cats and dogs

Two experiments are reported using a visual familiarization categorization procedure. In both experiments, infants were familiarized with sets of stimuli previously shown to contain asymmetric feature distributions that support an asymmetry in young infants' categorization of cats and dogs (i.e. infants' cat category excludes dogs but their dog category includes cats). In Experiment 1, the asymmetry was replicated in 4-month-old infants. In contrast, 10-month-old infants demonstrated exclusive category representations for both cats and dogs. In Experiment 2, an additional group of 10-month-olds demonstrated exclusive representations for both cats and dogs under conditions of very limited within-task category familiarization. Potential mechanisms underlying the shift from an asymmetric to a symmetric pattern of categorization in the first year are discussed.