The role of exemplar distribution in infants'' differentiation of categories

Three experiments investigated how the frequency of exposure to particular exemplars influenced 10-month-old infants' differentiation of land and sea animals in an object-examining task. In Experiments 1 and 2, one category exemplar was presented more frequently than the others during familiarization (i.e., that exemplar was presented on 6 of 12 familiarization trials, and 3 other exemplars were each presented on 2 familiarization trials). For half of the infants, the frequent exemplar was similar to other category exemplars (e.g., a zebra if the familiarization category was land animals), and for half the frequent exemplar was not similar to many other category exemplars (e.g., a rabbit). Infants who frequently experienced the similar exemplar formed an exclusive category, and differentiated land and sea animals. Infants who frequently experienced a dissimilar exemplar, in contrast, formed an inclusive category, and failed to differentiate between land and sea animals. In Experiment 3, infants received frequent experience with a set of similar or dissimilar exemplars, and the same pattern was observed. Thus, 10-month-old infants are sensitive to the distribution of the exemplars to which they are exposed, and they form different category boundaries depending on that distribution.     

The nature and structure of infant form categories

The nature of form categories in 3 to 4-month infants was studied using the visual preference for novelty in the familiarization-novelty paradigm. Novelty preference indicates habituation to and recognition of the familiar. In a series of experiments employing three form categories composed of dot patterns, generalized habituation to new category members was used to assess categorization behavior in the recognition of visual forms. At 3 to 4 months of age, infants did not initially show any systematic preferences for “good” or symmetrical examples of a category relative to “distorted” examples (Experiment 1) and this was true for all three form categories used (i.e., square, triangle, and diamond). Evidence for categorization was seen in the recognition performance of 3- to 4-month infants (Experiment 2). Infants showed generalized habituation to the previously unseen category prototypes following exposure to six exemplars within each of the three form categories. Given evidence that infants could discriminate between the prototype and other category members (Experiment 3), “inability to discriminate” was ruled out as an explanation for this form categorization or generalized habituation effect. Four subsequent experiments were conducted to determine whether infants exhibit a prototypicality structure for their remembered categories and whether certain conditions which have been shown to enhance prototypicality effects with adults have similar effects with infants. No evidence of a prototypicality structure was found for the form categories of infants when the number of exemplars during familiarization was limited to 6 and the test for form recognition followed immediately (Experiment 4). However, a prototypicality structure for the remembered form categories was found when a 3-min delay was introduced between familiarization and tests for form recognition (Experiment 5), when 12 exemplars were presented during familiarization (Experiment 7), or when the prototype was included as one of the six exemplars during the familiarization period (Experiment 6).     

Preparing for novelty with diverse training

This study investigated the ability to generalize acquired skills from training conditions to novel conditions, in a complex perceptual and cognitive task of luggage screening. We examined category and exemplar diversity during training for preparing learners to detect novel items during transfer. Category diversity was manipulated in terms of heterogeneity of training categories: Participants either trained with targets from one category or with targets from several categories. Exemplar diversity was manipulated between participants by presenting either a few or many exemplars for both category diversity conditions. Seventy‐two participants were trained to identify threats in pieces of luggage. Thereafter they were transferred to novel stimuli. Results can be summarized in support for the diversity of training hypothesis for preparing for novelty: To the best training for novel luggage screening situations is achieved using fewer items in a variety of categories. Copyright © 2010 John Wiley & Sons, Ltd.     

Three-month-old infants' categorization of animals and vehicles based on static and dynamic attributes.

Three-month-old infants' categorization of animals and vehicles based on static and dynamic attributes was investigated using a multiple-exemplar habituation-test paradigm. Half of the infants viewed static color images of animals and vehicles, and the other half viewed dynamic point-light displays of the same animals and vehicles. Following habituation, infants viewed a novel exemplar from the habituation category and an exemplar from a novel category. Regardless of whether they viewed static or dynamic displays, infants showed habituation to varying exemplars from the same category, generalized habituation to a novel exemplar from the habituation category, dishabituated to an exemplar from a novel category, and showed a significant novelty preference for a novel-category exemplar. These findings suggest that infants categorize animals and vehicles using either static or dynamic information.     

The influence of category representations on exemplar generation

The present study examined the influence of category representations on exemplar generation, which has been neglected in previous category research. An experiment on college students manipulated the category representation of insects in three conditions (prototypes, exemplars, and the hybrid of prototypes and exemplars). Participants were asked to generate as many exemplars as possible. The results demonstrate that category representations affect and constrain exemplar generation. The new findings are as follows. In the prototype and hybrid conditions with the prototype representation, people tend to generate more valid exemplars by using the prototype mutation mechanism, and exemplar generation conforms to the family resemblance structure. Exemplar generation in the hybrid condition is additionally constrained by known exemplars. In the exemplar condition, people tend to generate fewer valid exemplars by using miscellaneous strategies, and their exemplar generation may not conform to the family resemblance structure.     

A little labeling goes a long way: Semi‐supervised learning in infancy

There is considerable evidence that labeling supports infants' object categorization. Yet in daily life, most of the category exemplars that infants encounter will remain unlabeled. Inspired by recent evidence from machine learning, we propose that infants successfully exploit this sparsely labeled input through “semi‐supervised learning.” Providing only a few labeled exemplars leads infants to initiate the process of categorization, after which they can integrate all subsequent exemplars, labeled or unlabeled, into their evolving category representations. Using a classic novelty preference task, we introduced 2‐year‐old infants (n = 96) to a novel object category, varying whether and when its exemplars were labeled. Infants were equally successful whether all exemplars were labeled (fully supervised condition) or only the first two exemplars were labeled (semi‐supervised condition), but they failed when no exemplars were labeled (unsupervised condition). Furthermore, the timing of the labeling mattered: when the labeled exemplars were provided at the end, rather than the beginning, of familiarization (reversed semi‐supervised condition), infants failed to learn the category. This provides the first evidence of semi‐supervised learning in infancy, revealing that infants excel at learning from exactly the kind of input that they typically receive in acquiring real‐world categories and their names.     

The effect of category variability in perceptual categorization

Exemplar and distributional accounts of categorization make differing predictions for the classification of a critical exemplar precisely halfway between the nearest exemplars of 2 categories differing in variability. Under standard conditions of sequential presentation, the critical exemplar was classified into the most similar, least variable category, consistent with an exemplar account. However, if the difference in variability is made more salient, then the same exemplar is classified into the more variable, most likely category, consistent with a distributional account. This suggests that participants may be strategic in their use of either strategy. However, when the relative variability of 2 categories was manipulated, participants showed changes in the classification of intermediate exemplars that neither approach could account for.     

Infants' object category formation and use: Real-world context effects on category use in object processing

Three experiments investigated category formation based on real-world encounters with objects and how that category knowledge functioned as a top-down influence on infants' scene processing. 5-month-old infants received various experiences with exemplars of an object category and then were shown a display containing 2 adjacent novel objects, 1 of which was a novel exemplar of the category. If infants recognized this novel exemplar, they could use category information to determine the boundary between the 2 objects. Only infants who experienced object exemplars in situations that closely mimicked everyday infant experiences with objects successfully parsed the display. Results suggest that regularities in the contexts where infants experience similar objects help infants link their experiences and form object categories that can be used to segregate novel scenes. These results shed light on the real-world process of infant knowledge base formation and on how infants use their knowledge base to segment real-world scenes.     

Infant categorization: memory for category-level and specific item information

In an attempt to determine whether it is necessary to postulate abstraction processes in infant categorization, three experiments assessed retention of category-level information and information specific to category members. Using a visual recognition memory procedure, 10- and 13-month-old infants were familiarized with category instances containing both shared dimensional information and idiosyncratic features. The addition of idiosyncratic features to members of the familiarization category enhanced specific item memory for 13-month-old infants. However, this was not the case for the younger infants. The results of within-category test comparisons indicated that 10-month-old infants regarded information common to all members of the category as more familiar than information specific to individual exemplars. This occurred despite evidence that specific item information was retained in memory and available for retrieval during recognition tests. The findings are discussed in relation to exemplar and abstraction models of categorization.     

Physiological and behavioral parameters of infants' categorization: changes in heart rate and duration of examining across trials

This report investigates the relations between duration of examining and heart rate (HR) across several trials of an object-examination task. A total of N= 20 11-month-olds were familiarized with a sequence of 10 different exemplars from the same global category (animals or furniture) before they received an exemplar from the contrasting category at test. Consistent with previous findings, HR was lower during states of focused attention (i.e. examining) than during states of casual attention (i.e. looking) or non-looking. Over the familiarization trials, examining stayed about the same, while mean HR increased. At test, examining increased and mean HR decreased, indicating that infants focused their attention on the out-of-category object. Psychophysiological and behavioral measures of attention were systematically related over trials, suggesting that heart rate provides a suitable objective measure to study infants' categorization performance in object-examination tasks.     

Categorization in infancy based on novelty and co-occurrence

Abstract categories (i.e., groups of objects that do not share perceptual features, such as food) abound in everyday situations. The present looking time study investigated whether infants are able to distinguish between two abstract categories (food and toys), and how this ability may extend beyond perceived information by manipulating object familiarity in several ways. Test trials displayed 1) the exact familiarized objects paired as they were during familiarization, 2) a cross-pairing of these same familiar objects, 3) novel objects in the same category as the familiarized items, or 4) novel objects in a different category. Compared to the most familiar test trial (i.e., Familiar Category, Familiar Objects, Familiar Pairings), infants looked longer to all other test trials. Although there was a linear increase in looking time with increased novelty of the test trials (i.e., Novel Category as the most novel test trial), the looking times did not differ significantly between the Novel Category and Familiar Category, Unfamiliar Objects trials. This study contributes to our understanding of how infants form object categories based on object familiarity, object co-occurrence, and information abstraction.     

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.     

Memory storage and retrieval processes in category learning

The detailed course of learning is studied for categorization tasks defined by independent or contingent probability distributions over the features of category exemplars. College-age subjects viewed sequences of bar charts that simulated symptom patterns and responded to each chart with a recognition and a categorization judgment. Fuzzy, probabilistically defined categories were learned relatively rapidly when individual features were correlated with category assignment, more slowly when only patterns carried category information. Limits of performance were suboptimal, evidently because of capacity limitations on judgmental processes as well as limitations on memory. Categorization proved systematically related to feature and exemplar probabilities, under different circumstances, and to similarity among exemplars of categories. Unique retrieval cues for exemplar patterns facilitated recognition but entered into categorization only at retention intervals within the range of short-term memory. The findings are interpreted within the framework of a general array model that yields both exemplar-similarity and feature-frequency models as special cases and provides quantitative accounts of the course of learning in each of the categorization tasks studied.     

Object names and object functions serve as cues to categories for infants

Can object names and functions act as cues to categories for infants? In Study 1, 14- and 18-month-old infants were shown novel category exemplars along with a function, a name, or no cues. Infants were then asked to "find another one," choosing between 2 novel objects (1 from the familiar category and the other not). Infants at both ages were more likely to select the category match in the function than in the no-cue condition. However, only at 18 months did naming the objects enhance categorization. Study 2 shows that names can facilitate categorization for 14-month-olds as well when a hint regarding the core meaning of the objects (the function of a single familiarization object) is provided.     

Infants' formation and use of categories to segregate objects

Four- and-a-half-month-old infants' (N = 100) category formation and use was studied in a series of five experiments. For each experiment, the test events featured a display composed of a cylinder and a box. Previous research showed that this display is not clearly parsed as a single unit or as two separate units by infants of this age. Immediately prior to testing, infants were shown a set of category exemplars. Knowledge about this category could help infants disambiguate the test display, which contained a novel exemplar of this category. Clear interpretation of the test display as composed of two separate units (as indicated by infants' longer looking at the move-together than at the move-apart test event) was taken as evidence of category formation and use. In Experiments 1 and 5, infants' prior experience with a set of three different boxes that were similar to the test box facilitated their segregation of the test display. Experiment 2 showed that three different exemplars are necessary: prior experience with any two of the three boxes used in Experiment 1 did not facilitate infants' segregation of the test display. Experiment 3 showed that variability in the exemplar set is necessary: prior experience with three identical boxes did not facilitate infants' segregation of the test display. Experiment 4 showed that under these conditions of very brief prior exposure, similarity between the exemplar set and test box is necessary: prior experience with three different boxes that were not very similar to the test box did not facilitate infants' segregation of the test display. Together, these findings suggest that: (a) number of exemplars, variability, and similarity in the exemplar set are important for infants' category formation, and (b) infants use their category knowledge to determine the boundaries of the objects in a display.     

Development of category formation for faces differing by age in 9‐ to 12‐month‐olds: An effect of experience with infant faces

We examined category formation for faces differing in age in 9‐ and 12‐month‐olds, and the influence of exposure to infant faces on such ability. Infants were familiarized with adult or infant faces, and then tested with a novel exemplar from the familiarized category paired with a novel exemplar from a novel category (Experiment 1). Both age groups formed discrete categories of adult and infant faces, but exposure to infant faces in everyday life did not modulate performance. The same task was conducted with child versus infant faces (Experiment 2). Whereas 9‐month‐olds preferred infant faces after familiarization with child faces, but not child faces after familiarization with infant faces, 12‐month‐olds formed discrete categories of child and infant faces. Moreover, more exposure to infant faces correlated with higher novel category preference scores when infants were familiarized with infant faces in 12‐month‐olds, but not 9‐month‐olds. The 9‐month‐old asymmetry did not reflect spontaneous preference for infant over child faces (Experiment 3). These findings indicate that 9‐ and 12‐month‐olds can form age‐based categories of faces. The ability of 12‐month‐olds to form separate child and infant categories suggests that they have a more exclusive representation of face age, one that may be influenced by prior experience with infant faces.     

知道与不知道要学多少：类别学习中样例量的预期作用

采用“5/4模型”类别结构探讨了类别学习中样例量的预期作用。设置了两种学习条件(“知道样例量”和“不知道样例量”), 分别探讨两种学习条件下的学习效率、学习策略以及所形成的类别表征。106名大学生参加了实验, 结果表明：在类别学习中, 样例量的预期作用显著, 知道样例量组的学习效率高于不知道样例量组; 样例量的预期作用对类别学习效率的影响是通过影响学习过程中使用的策略来实现的; 样例量的预期作用不影响两种学习条件的学习后形成的类别表征, 且两种学习条件的被试自始至终表现出样例学习的表征模式。     

Does category-training facilitate 11-month-olds’ acquisition of unfamiliar category-property associations?

The ability to form category-property links allows infants to extend a property from one category member to another. In two experiments, we examined whether orienting infants to the demands of the task, through categorization training, would facilitate 11-month-old infants’ category-property extensions when familiarized with a single exemplar of an unfamiliar animal category. In Experiment 1, 11-month-olds (N = 35) were trained with two familiar animal-sound pairings (i.e., dog-bark, cat-meow), familiarized with two unfamiliar animal-sound pairings and then tested on their learning and generalization of the unfamiliar animal-sound associations. Across two conditions, Experiment 2 familiarized 11-month-olds (N = 69) to one familiar (i.e., dog-bark) and one novel animal-sound pairing. Conditions differed in their presentation of familiarization trials (i.e., random or blocked). Infants were then tested on their learning and extension of the animal-sound associations. In both experiments, infants did not demonstrate learning of the original animal sound pairing, nor generalization of the sound property to new members of the animal categories. These results indicate that the two category training paradigms implemented in the current studies did not facilitate 11-month-olds’ ability to learn or generalize an unfamiliar animal-sound association, when familiarized with a single exemplar.     

Monitoring of learning at the category level when learning a natural concept: Will task experience improve its resolution?

Researchers have recently begun to investigate people's ability to monitor their learning of natural categories. For concept learning tasks, a learner seeks to accurately monitor learning at the category level — i.e., to accurately judge whether exemplars will be correctly classified into the appropriate category on an upcoming test. Our interest was in whether monitoring resolution at the category level would improve as participants gain task experience across multiple study-test blocks, as well as within each block. In four experiments, exemplar birds (e.g., American Goldfinch, Cassin's Finch) paired with each family name (e.g., Finch) were studied, and participants made a judgment of learning (JOL) for each exemplar. Of most interest, before and after studying the exemplars, participants made category learning judgments (CLJs), which involved predicting the likelihood of correctly classifying novel birds into each family. Tests included exemplars that had been studied or exemplars that had not been studied (novel). This procedure was repeated for either one or two additional blocks. The relative accuracy of CLJs did not improve across blocks even when explicit feedback was provided, whereas item-by-item JOL accuracy improved across blocks. Category level resolution did improve from pre-study to post-study on an initial block, but it did not consistently increase within later blocks. The stable accuracy of CLJs across blocks poses a theoretical and empirical challenge for identifying techniques to improve people's ability to judge their learning of natural categories.     

The memory representation of motor skills: a test of schema theory

Currently, a popular model for the central representation of motor skills is embodied in Schmidt's schema theory of discrete motor skill learning (Schmidt, 1975). Two experiments are reported here that contrast predictions from a schema abstraction model that is the basis for schema theory with those from an exemplar-based model of motor skill memory representation. In both experiments, subjects performed 300 trials per day of three variations of a three-segment timing task over 4 days of acquisition. The subjects then either immediately transferred to four novel variations of the same task (Experiment 1) that varied in degree of similarity to the exemplars experienced during acquisition; or performed two novel and two previously produced exemplars, following 24-h and 1-week retention intervals (Experiment 2). The results indicated that novel task transfer was not affected by the degree of similarity between the acquisition and transfer exemplars, and that there was no advantage for a previously produced exemplar over a novel exemplar after either a 24-hr or 1 week retention interval. Also, in both experiments, a consistent pattern of bias in responding was noted for novel task transfer and retention. These results are indicative of a schema abstraction model of memory representation for motor skills.