Beyond prototypes: asymmetries in infant categorization and what they teach us about the mechanisms guiding early knowledge acquisition

Infants' Daily Experience With Pets and Their Scanning of Animal Faces

Very little is known about the effect of pet experience on cognitive development in infancy. In Experiment 1, we document in a large sample (N = 1270) that 63% of families with infants under 12 months have at least one household pet. The potential effect on development is significant as the first postnatal year is a critically important time for changes in the brain and cognition. Because research has revealed how experience shapes early development, it is likely that the presence of a companion dog or cat in the home influences infants' development. In Experiment 2, we assess differences between infants who do and do not have pets (N = 171) in one aspect of cognitive development: their processing of animal faces. We examined visual exploration of images of dog, cat, monkey, and sheep faces by 4-, 6-, and 10-month-old infants. Although at the youngest ages infants with and without pets exhibited the same patterns of visual inspection of these animals faces, by 10 months infants with pets spent proportionately more time looking at the region of faces that contained the eyes than did infants without pets. Thus, exposure to pets contributes to how infants look at and learn about animal faces.

Infants' Differential Processing of Female and Male Faces

Infants show an interesting asymmetry in face processing: They are more fluent in processing female faces than they are at processing male faces. We hypothesize that such processing asymmetry results from greater experience with female faces than with male faces early in development. Asymmetrical face processing may have long-lasting implications for development of face recognition, development of knowledge structures regarding females and males, and social-information processing. We encourage researchers to use both female and male faces in their face-perception research and to conduct separate analyses for female and male faces.

Preexisting Knowledge Versus On-Line Learning

Contemporary knowledge of infant cognition relies heavily on violation-of-expectation experiments. However, there are two ways to conceptualize what occurs in such studies. Babies may react to anomalous test events because of preexisting world knowledge. Alternatively, they may react because they have learned about events during the familiarization period. One way to distinguish these possibilities is to contrast familiarization with everyday versus anomalous events. In the studies we report here, we used this method to probe the nature of 5-month-olds' expectations about the locations of objects hidden in sand and later revealed. In Experiment 1, infants who initially saw everyday events did react to anomalous ones, as found previously, whereas infants who initially saw anomalous events did not react to everyday events. In Experiment 2, two alternative explanations of this pattern were ruled out. We conclude that by the age of 5 months, infants have expectations regarding the location of objects in continuous space.

Asymmetries in infants' attention toward and categorization of male faces: The potential role of experience

Infants typically have a preponderance of experience with females, resulting in visual preferences for female faces, particularly high attractive females, and in better categorization of female relative to male faces. We examined whether these abilities generalized to infants' visual preferences for and categorization of perceptually similar male faces (i.e., low masculine males). We found that 12-month-olds visually preferred high attractive relative to low attractive male faces within low masculine pairs only (Experiment 1) but did not visually prefer low masculine relative to high masculine male faces (Experiment 2). Lack of visual preferences was not due to infants' inability to discriminate between the male faces (Experiments 3 and 4). The 12-month-olds categorized low masculine, but not high masculine, male faces (Experiment 5). Infants could individuate male faces within each of the categories (Experiment 6). The 12-month-olds' attention toward and categorization of male faces may reflect a generalization of their female facial expertise.

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.

Asian infants show preference for own-race but not other-race female faces: the role of infant caregiving arrangements

Previous studies have reported that 3- to 4-month-olds show a visual preference for faces of the same gender as their primary caregiver (e.g., Quinn et al., 2002). In addition, this gender preference has been observed for own-race faces, but not for other-race faces (Quinn et al., 2008). However, most of the studies of face gender preference have focused on infants at 3–4 months. Development of gender preference in later infancy is still unclear. Moreover, all of these studies were conducted with Caucasian infants from Western countries. It is thus unknown whether a gender preference that is limited to own-race faces can be generalized to infants from other racial groups and different cultures with distinct caregiving practices. The current study investigated the face gender preferences of Asian infants presented with male versus female face pairs from Asian and Caucasian races at 3, 6, and 9 months and the role of caregiving arrangements in eliciting those preferences. The results showed an own-race female face preference in 3- and 6-month-olds, but not in 9-month-olds. Moreover, the downturn in the female face preference correlated with the cumulative male face experience obtained in caregiving practices. In contrast, no gender preference or correlation between gender preference and face experience was found for other-race Caucasian faces at any age. The data indicate that the face gender preference is not specifically rooted in Western cultural caregiving practices. In addition, the race dependency of the effect previously observed for Caucasian infants reared by Caucasian caregivers looking at Caucasian but not Asian faces extends to Asian infants reared by Asian caregivers looking at Asian but not Caucasian faces. The findings also provide additional support for an experiential basis for the gender preference, and in particular suggest that cumulative male face experience plays a role in inducing a downturn in the preference in older infants.

African Versus Caucasian Faces in a Visual Expectation Paradigm

This article focuses on sequence learning on the Visual Expectation Paradigm (VExP) using human faces as stimulus material. For a sample of 133 Caucasian German infants assessed longitudinally at 3 and 6 months of age, a previous study has shown that the response latency of 6-month-old infants was shorter when the infants solved the task with Caucasian own-race faces in contrast to African other-race faces. The advantage for own-race faces occurs at the same age the Other-Race-Effect (ORE) has been reported to emerge. As studies on ORE development have shown the phenomenon in infants from various cultural backgrounds, the follow-up question to be answered here is whether the performance differences on the VExP can also be found in other than Caucasian infants. As a complement to the German sample, 30 African infants from Cameroon were assessed longitudinally with the same VExP task at ages 3 and 6 months. Our results indicate that perception differences between own-race and other-race faces influence performance on the VExP in both samples. As expected, the Cameroonian infants improved performance on the VExP from 3 to 6 months only in their own-race African faces condition.

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.

Correspondences between what infants see and know about causal and self-propelled motion

The associative learning account of how infants identify human motion rests on the assumption that this knowledge is derived from statistical regularities seen in the world. Yet, no catalog exists of what visual input infants receive of human motion, and of causal and self-propelled motion in particular. In this manuscript, we demonstrate that the frequency with which causal agency and self-propelled motion appear in the visual environment predicts infants' understanding of these motions. In an observational study, an infant wearing a head-mounted camera saw people act as agents in causal events three times more often than he saw people engaged in self-propelled motion. Subsequent experiments with the habituation paradigm revealed that infants begin to generalize self-propulsion to agents in causal events between 10 and 14 months of age. However, infants cannot generalize causal agency to a self-propelled object at 14 or 18 months unless the object exhibits additional cues to animacy. The results are discussed within a domain-general framework of learning about human action.

Exploring the perceptual spaces of faces, cars and birds in children and adults

While much developmental research has focused on the strategies that children employ to recognize faces, less is known about the principles governing the organization of face exemplars in perceptual memory. In this study, we tested a novel, child-friendly paradigm for investigating the organization of face, bird and car exemplars. Children ages 3-4, 5-6, 7-8, 9-10, 11-12 and adults were presented with 50/50 morphs of typical and atypical face, bird and car parent images. Participants were asked to judge whether the 50/50 morph more strongly resembled the typical or the atypical parent image. Young and older children and adults showed a systematic bias to the atypical faces and birds, but no bias toward the atypical cars. Collectively, these findings argue that by the age of 3, children encode and organize faces, birds and cars in a perceptual space that is strikingly similar to that of adults. Category organization for both children and adults follows Krumhansl's (1978) distance-density principle in which the similarity between two exemplars is jointly determined by their physical appearance and the density of neighboring exemplars in the perceptual space.

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 "Humpty Dumpty Problem" in the Study of Early Cognitive Development: Putting the Infant Back Together Again

In this article, I propose that the big question for the field of infant cognitive development is best characterized as the "Humpty Dumpty problem": Now that we have studied cognitive abilities in isolation, how do we put the developing cognitive system (and the infant) back together again? This problem is significant because cognitive abilities do not occur in isolation. Infants remember the items they have attended to and perceived, and their emotional state will influence their perception and representation of the events they encounter. Moreover, by examining the development of the whole cognitive system, or the whole child, we gain a deeper understanding of mechanisms developmental change. Thus, the big question for the study of infant cognition is like the question confronting all the king's horses and all the king's men: How do we put the infant's cognitive system back together again?

Facial experience during the first year

Parents of 2-, 5-, 8-, and 11-month-olds used two scales we developed to provide information about their infants' facial experience with familiar and unfamiliar individuals during one week. Results showed large discrepancies in the race, sex, and age of faces that infants experience during their first year with the majority of their facial experience being with their primary caregiver, females, and other individuals of the same-race and age as their primary caregiver. The infant's age and an unfamiliar individual's sex were predictive of their time spent interacting with one another. Moreover, an unfamiliar individual's sex was predictive of the attention infants allocated during social interactions. Differences in frequency and length of interactions with certain types of faces, as well as in infant attention toward certain individuals, all likely contribute to the development of expertise in processing commonly experienced face types and deficiencies in processing less commonly experienced face types.

Preference for attractive faces in human infants extends beyond conspecifics

Human infants, just a few days of age, are known to prefer attractive human faces. We examined whether this preference is human-specific. Three- to 4-month-olds preferred attractive over unattractive domestic and wild cat (tiger) faces (Experiments 1 and 3). The preference was not observed when the faces were inverted, suggesting that it did not arise from low-level image differences (Experiments 2 and 3). In addition, the spontaneous preference for attractive tiger faces influenced performance in a recognition memory task involving attractive versus unattractive tiger face pairings (Experiment 4). The findings suggest that infant preference for attractive faces reflects the activity of general processing mechanisms rather than a specific adaptation to mate choice.

Conditions for young infants' perception of object trajectories

When an object moves behind an occluder and re-emerges, 4-month-old infants perceive trajectory continuity only when the occluder is narrow, raising the question of whether time or distance out of sight is the important constraining variable. One hundred and forty 4-month-olds were tested in five experiments aimed to disambiguate time and distance out of sight. Manipulating the object's visible speed had no effect on infants' responses, but reducing occlusion time by increasing object speed while occluded induced perception of trajectory continuity. In contrast, slowing the ball while it was behind a narrow or intermediate screen did not modify performance. It is concluded that 4-month-olds perceive trajectory continuity when time or distance out of sight is short.

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.

Is the asymmetry in young infants' categorization of humans versus nonhuman animals based on head, body, or global gestalt information?

Quinn and Eimas (1998) reported an asymmetry in the exclusivity of the category representations that young infants form for humans and nonhuman animals: category representations for nonhuman animal species were found to exclude humans, whereas a category representation for humans was found to include nonhuman animal species (i.e., cats, horses). The present experiment utilized the familiarization/novelty-preference procedure with 3- and 4-month-olds to determine the perceptual cues (i.e., whole stimulus, head alone, body alone) that provided the basis for this asymmetry. The data revealed the asymmetry to be observable only with the whole animal stimuli and not when infants were provided with information from just the head or the body of the exemplars. The results indicate that the incorporation of nonhuman animal species into a category representation for humans is based on holistic information.

Basic-level category discriminations by 7- and 9-month-olds in an object examination task

This study examines 7- and 9-month-olds' ability to categorize cats as separate from dogs, and dogs as separate from cats in an object examination task. In Experiment 1, 7- and 9-month-olds (N = 30) familiarized with toy cat replicas were found to form a category of cat that included novel cats but excluded a dog and an eagle. In Experiment 2, 7- and 9-month-olds (N = 30) familiarized with toy dog replicas were found to form a category of dog that included a novel dogs and a novel cat but excluded an eagle. These results mirror those of 3- to 4-month-olds tested with visual preference methods and stand in contrast to previously reported object examination results. Analyses of the distribution of features in the exemplars used to familiarize infants suggest that, like the 3- to 4-month-olds, the 7- and 9-month-olds in these studies form categories within the task, and on the basis of feature distributions.

Representation of the gender of human faces by infants: a preference for female

Six experiments based on visual preference procedures were conducted to examine gender categorization of female versus male faces by infants aged 3 to 4 months. In experiment 1, infants familiarized with male faces preferred a female face over a novel male face, but infants familiarized with female faces divided their attention between a male face and a novel female face. Experiment 2 demonstrated that these asymmetrical categorization results were likely due to a spontaneous preference for females. Experiments 3 and 4 showed that the preference for females was based on processing of the internal facial features in their upright orientation, and not the result of external hair cues or higher-contrast internal facial features. While experiments 1 through 4 were conducted with infants reared with female primary caregivers, experiment 5 provided evidence that infants reared with male primary caregivers tend to show a spontaneous preference for males. Experiment 6 showed that infants reared with female primary caregivers displayed recognition memory for individual females, but not males. These results suggest that representation of information about human faces by young infants may be influenced by the gender of the primary caregiver.