Natural concepts in a juvenile gorilla (gorilla gorilla gorilla) at three levels of abstraction

The extent to which nonhumans are able to form conceptual versus perceptual discriminations remains a matter of debate. Among the great apes, only chimpanzees have been tested for conceptual understanding, defined as the ability to form discriminations not based solely on simple perceptual features of stimuli, and to transfer this learning to novel stimuli. In the present investigation, a young captive female gorilla was trained at three levels of abstraction (concrete, intermediate, and abstract) involving sets of photographs representing natural categories (e.g., orangutans vs. humans, primates vs. nonprimate animals, animals vs. foods). Within each level of abstraction, when the gorilla had learned to discriminate positive from negative exemplars in one set of photographs, a novel set was introduced. Transfer was defined in terms of high accuracy during the first two sessions with the new stimuli. The gorilla acquired discriminations at all three levels of abstraction but showed unambiguous transfer only with the concrete and abstract stimulus sets. Detailed analyses of response patterns revealed little evidence of control by simple stimulus features. Acquisition and transfer involving abstract stimulus sets suggest a conceptual basis for gorilla categorization. The gorilla's relatively poor performance with intermediate-level discriminations parallels findings with pigeons, and suggests a need to reconsider the role of perceptual information in discriminations thought to indicate conceptual behavior in nonhumans.     

Attention, similarity, and the identification-categorization relationship

A unified quantitative approach to modeling subjects' identification and categorization of multidimensional perceptual stimuli is proposed and tested. Two subjects identified and categorized the same set of perceptually confusable stimuli varying on separable dimensions. The identification data were modeled using Shepard's (1957) multidimensional scaling-choice framework. This framework was then extended to model the subjects' categorization performance. The categorization model, which generalizes the context theory of classification developed by Medin and Schaffer (1978), assumes that subjects store category exemplars in memory. Classification decisions are based on the similarity of stimuli to the stored exemplars. It is assumed that the same multidimensional perceptual representation underlies performance in both the identification and categorization paradigms. However, because of the influence of selective attention, similarity relationships change systematically across the two paradigms. Some support was gained for the hypothesis that subjects distribute attention among component dimensions so as to optimize categorization performance. Evidence was also obtained that subjects may have augmented their category representations with inferred exemplars. Implications of the results for theories of multidimensional scaling and categorization are discussed.     

The differing roles of comparison and contrast in children’s categorization

Comparison of perceptually similar exemplars from an object category encourages children to overlook compelling perceptual similarities and use relational and functional properties more relevant for taxonomic categorization. This article investigates whether showing children a contrasting object that is perceptually similar but out of kind serves the same function as comparison in heightening children’s attention to taxonomically relevant features. In this study, 4-year-olds completed a forced-choice categorization task in which they viewed exemplars from a target category and then selected among (a) a perceptually similar out-of-kind object, (b) a category member that differed perceptually from the exemplars, and (c) a thematically related object. Children were assigned to one of four conditions: No-Compare/No-Contrast, Compare/No-Contrast, No-Compare/Contrast, or Compare/Contrast. As in previous work, comparison increased the frequency of category responses, but there was no effect of contrast on categorization. However, only those in the Compare/Contrast condition displayed consistently taxonomic patterns of responding. Follow-up studies revealed that the effect of comparison plus contrast was evident only when comparison preceded, rather than followed, contrast information and that the value added by providing contrastive information is not attributable to the perceptual similarity between the category exemplars and the contrast object. Comparison and contrast make differing contributions to children’s categorization.     

Facelikeness matters: A parametric multipart object set to understand the role of spatial configuration in visual recognition

There is a view that faces and objects are processed by different brain mechanisms. Different factors may modulate the extent to which face mechanisms are used for objects. To distinguish these factors, we present a new parametric multipart three-dimensional object set that provides researchers with a rich degree of control of important features for visual recognition such as individual parts and the spatial configuration of those parts. All other properties being equal, we demonstrate that perceived facelikeness in terms of spatial configuration facilitated performance at matching individual exemplars of the new object set across viewpoint changes (Experiment 1). Importantly, facelikeness did not affect perceptual discriminability (Experiment 2) or similarity (Experiment 3). Our findings suggest that perceptual resemblance to faces based on spatial configuration of parts is important for visual recognition even after equating physical and perceptual similarity. Furthermore, the large parametrically controlled object set and the standardized procedures to generate additional exemplars will provide the research community with invaluable tools to further understand visual recognition and visual learning.     

Classification in well-defined and ill-defined categories: evidence for common processing strategies

Early work in perceptual and conceptual categorization assumed that categories had criterial features and that category membership could be determined by logical rules for the combination of features. More recent theories have assumed that categories have an ill-defined structure and have prosposed probabilistic or global similarity models for the verification of category membership. In the experiments reported here, several models of categorization were compared, using one set of categories having criterial features and another set having an ill-defined structure. Schematic faces were used as exemplars in both cases. Because many models depend on distance in a multidimensional space for their predictions, in Experiment 1 a multidimensional scaling study was performed using the faces of both sets as stimuli, In Experiment 2, subjects learned the category membership of faces for the categories having criterial features. After learning, reaction times for category verification and typicality judgments were obtained. Subjects also judged the similarity of pairs of faces. Since these categories had characteristic as well as defining features, it was possible to test the predictions of the feature comparison model (Smith et al.), which asserts that reaction times and typicalities are affected by characteristic features. Only weak support for this model was obtained. Instead, it appeared that subjects developed logical rules for the classification of faces. A characteristic feature affected reaction times only when it was part of the rule system devised by the subject. The procedure for Experiment 3 was like that for Experiment 2, but with ill-defined rather than well-defined categories. The obtained reaction times had high correlations with some of the models for ill-defined categories. However, subjects' performance could best be described as one of feature testing based on a logical rule system for classification. These experiments indicate that whether or not categories have criterial features, subjects attempt to develop a set of feature tests that allow for exemplar classification. Previous evidence supporting probabilistic or similarity models may be interpreted as resulting from subjects' use of the most efficient rules for classification and the averaging of responses for subjects using different sets of rules.     

Perceptual processing affects the reactivation of a sensory dimension during a categorization task

According to grounded theories of cognition, knowledge is grounded in its sensory-motor features. Therefore, perceptual and conceptual processing should be based on the same distributed system so that conceptual and perceptual processes should interact. The present study assesses whether gustatory stimulation (participants tasted a sweet or a nonsweet yoghurt) could influence performance on a categorization task that involves the reactivation of the same sensory dimension. The results indicate that participants were slower (Experiment 1) or faster (Experiment 2), respectively, at categorizing pictures as representing edible sweet stimuli when they either simultaneously or had previously tasted a sweet yoghurt as compared to a nonsweet yoghurt. These results confirm the significant overlap between perceptual and memory mechanisms and suggest the functional equivalence between perceptually present and perceptually absent (memory reactivated) dimensions.     

Lateralized cognition: asymmetrical and complementary strategies of pigeons during discrimination of the "human concept"

This study was aimed at revealing which cognitive processes are lateralized in visual categorizations of "humans" by pigeons. To this end, pigeons were trained to categorize pictures of humans and then tested binocularly or monocularly (left or right eye) on the learned categorization and for transfer to novel exemplars (Experiment 1). Subsequent tests examined whether they relied on memorized features or on a conceptual strategy, using stimuli composed of new combinations of familiar and novel humans and backgrounds (Experiment 2), whether the hemispheres processed global or local information, using pictures with different levels of scrambling (Experiment 3), and whether they attended to configuration, using distorted human figures (Experiment 4). The results suggest that the left hemisphere employs a category strategy and concentrates on local features, while the right hemisphere uses an exemplar strategy and relies on configuration. These cognitive dichotomies of the cerebral hemispheres are largely shared by humans, suggesting that lateralized cognitive systems already defined the neural architecture of the common ancestor of birds and mammals.     

Hierarchical categorization by bilingual Latino children: does a basic-level bias exist?

Research has shown that children classify most easily at the basic level where objects in the same category look similar enough to each other to be grouped together but are distinct enough from objects in other categories to be discriminated (e.g., animal/bird/duck). In this article, the authors report on 2 experiments they conducted to determine whether children maintain this basic category bias when the perceptual similarity of stimuli at different hierarchical levels is equalized. Pictures within and across 3 hierarchical levels were made perceptually equivalent and shown to 71 Latino children who were bilingual in Spanish and English. In Experiment 1, the pictures used as exemplars could be categorized on any of the 3 hierarchical levels. In Experiment 2, example pictures unambiguously defined the level of categorization that would be accurate, and linguistic cues were given that might assist in the selection of the correct category. In both experiments, the children sorted pictures from all 3 levels equally well, but they found it harder to justify their sorting of superordinate pictures. English competence predicted sorting on the more ambiguous sorting task in Experiment 1; and English competence predicted verbal justifications in both experiments, even though the experiments were conducted in Spanish. Competence in Spanish or English was an equally good predictor of sorting in the better defined sorting task in Experiment 2. These findings indicate that a superordinate level deficiency remains after perceptual differences are eliminated and that the deficiency is cognitive in nature. Differences in the performances of children who differed in bilingualism support the hypothesis that a threshold of proficiency in both languages is an important determinant of the effect of bilingualism on categorization.     

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).     

A ROWS is a ROSE: Spelling,sound, and reading

Skilled readers generally are assumed to make little or no use of words’ phonological features in visual word identification. Contrary to this assumption, college students’ performance in the present reading experiments showed large effects of stimulus word phonology. In Experiments 1 and 2, these subjects produced larger false positive error rates in a semantic categorization task when they responded to stimulus foils that were homophonic to category exemplars (e.g., ROWS for the category A FLOWER) than when they responded to spelling control foils. Additionally, in Experiment 2, this homophony effect was found under brief-exposure pattern-masking conditions, a result consistent with the possibility that phonology is an early source of constraint in word identification. Subjects did, however, correctly reject most homophone foils in Experiments 1 and 2. Experiment 3 investigated the source of this ability. The results of Experiment 3 suggest that subjects detected homophone impostors, such as ROWS, by verifying target foil spellings against their knowledge of the correct spellings of category exemplars, such as ROSE.     

类别学习的阻碍效应与双机制理论

通过对类别学习中的阻碍效应进行系统研究,尝试性的提出了类别学习的双机制理论。三个实验分别考察：当样例特征随机呈现时;定义特征固定呈现在样例首位时;以及刺激材料为知觉图形材料时,类别学习中的阻碍效应。三个实验的研究结果都发现：在类别学习中存在一定程度的阻碍效应,支持类别学习同时存在联结学习机制和认知学习机制的双机制观点。     

Asymmetric interference in 3‐ to 4‐month‐olds' sequential category learning

Three‐ to 4‐month‐old infants show asymmetric exclusivity in the acquisition of cat and dog perceptual categories. The cat perceptual category excludes dog exemplars, but the dog perceptual category does not exclude cat exemplars. We describe a connectionist autoencoder model of perceptual categorization that shows the same asymmetries as infants. The model predicts the presence of asymmetric retroactive interference when infants acquire cat and dog categories sequentially. A subsequent experiment conducted with 3‐ to 4‐month‐olds verifies the predicted pattern of looking time behaviors. We argue that bottom‐up, associative learning systems with distributed representations are appropriate for modeling the operation of short‐term visual memory in early perceptual category learning.     

类别不确定下的特征推理是基于类别还是基于特征联结

共有3个实验探讨归类不确定情况下的特征推理是基于类别进行还是基于特征联结进行。实验1在中文条件下重复了Verde等人2005的实验,得出了与之相符的结果,这个结果用基于类别的理性模型的设想或者是用基于特征联结的设想都可以解释。实验2考察被试在靶类别的类别特征频次并且特征结合出现频次高低不同的条件下特征推理的情况,实验2的结果表明,高集中与低集中两种条件下特征推理没有显著差异,不符合特征推理是基于类别进行的设想,而与特征推理是基于特征联结进行的设想吻合。实验3进一步考察被试在特征结合出现的总频次并且靶类别中特征结合出现的总频次高低不同的条件下特征推理的情况,结果表明,在高结合条件下进行特征推理要优于在低结合条件,支持了在归类不确定情况下的特征推理是基于特征联结进行的设想。据此可以认为,人们的特征推理是基于特征之间联结的频次进行,而不是基于类别进行     

Influence of familiar features on diagnosis: instantiated features in an applied setting

Medical diagnosis can be viewed as a categorization task. There are two mechanisms whereby humans make categorical judgments: "analytical reasoning," based on explicit consideration of features and "nonanalytical reasoning," an unconscious holistic process of matching against prior exemplars. However, there is evidence that prior experience can also operate at the level of individual "instantiated" features (Brooks & Hannah, 2006). The present studies examined instantiated features in medical diagnosis. Four "pseudopsychiatric" conditions, each described by four characteristic features, were taught to undergraduate psychology students. They practiced on additional cases, then were tested on new cases with features from two conditions. In Experiment 1, diagnoses associated with familiar features presented one or three times during practice were assigned a higher probability than those with novel features. Experiment 2 showed that the impact of feature frequency was dependent on its consistency with the case diagnosis. Experiment 3 showed that the effect of feature familiarity was not confined to cases with two equiprobable diagnoses. Experiment 4 showed that the effect remained after a 24 hour delay. These four studies demonstrated that features seen in practice have a greater influence on diagnosis than novel synonyms. In fact, seeing a feature once within the appropriate context (a patient case in which it is a member of the primary diagnosis) was sufficient to form a diagnostic association equivalent to instantiations seen four times in a different context. The results of these studies have implications for theories of categorization and for teaching clinical reasoning.     

知觉适应对种族融合面孔的种族分类和知觉辨别的影响

面孔加工的种族效应(the other-race effects)指人们对面孔做个体辨别任务时辨别本族面孔的绩效优于辨别他族面孔的绩效, 而做种族分类任务时分类他族面孔的绩效优于分类本族面孔的绩效。本研究通过知觉适应操纵被试对种族两歧(高加索和亚洲)融合面孔的种族知觉, 进而比较被试在两种条件下对同一张融合面孔进行种族分类和知觉辨别的绩效的差异。结果发现, 知觉适应能使被试产生将两歧融合面孔知觉为与原始面孔所属种族相反种族的知觉偏向, 并且, 伴随着这种知觉偏向, 两歧融合面孔的加工出现了他族分类优势和本族辨别优势, 提示社会认知因素对面孔加工的种族效应有重要作用。     

The nature of infant color categorization: evidence from eye movements on a target detection task

Infants respond categorically to color. However, the nature of infants' categorical responding to color is unclear. The current study investigated two issues. First, is infants' categorical responding more absolute than adults' categorical responding? That is, can infants discriminate two stimuli from the same color category? Second, is color categorization in infants truly perceptual? Color categorization was tested by recording adults' and infants' eye movements on a target detection task. In Experiment 1, adults were faster at fixating a colored target when it was presented on a colored background from a different color category (between-category) than when it was presented on a colored background from the same color category (within-category), even when within- and between-category chromatic differences were equated in CIE (Committee International d'Eclairage) color space. This category effect was found for two chromatic separation sizes. In Experiment 2, 4-month-olds also responded categorically on the task. Infants were able to fixate the target when the background color was from the same category. However, as with adults, infants were faster at fixating the target when the target background chromatic difference was between-category than when it was within-category. This implies that infant color categorization, like adult color categorization, is truly perceptual.     

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.     

Transfer to intermediate forms following concept discrimination by pigeons: chimeras and morphs

Two experiments examined pigeons' generalization to intermediate forms following training of concept discriminations. In Experiment 1, the training stimuli were sets of images of dogs and cats, and the transfer stimuli were head/body chimeras, which humans tend to categorize more readily in terms of the head part rather than the body part. In Experiment 2, the training stimuli were sets of images of heads of dogs and cats, and the intermediate stimuli were computer-generated morphs. In both experiments, pigeons learned the concept discrimination quickly and generalized with some decrement to novel instances of the categories. In both experiments, transfer tests were carried out with intermediate forms generated from both familiar and novel exemplars of the training sets. In Experiment 1, the pigeons' transfer performance, unlike that of human infants exposed to similar stimuli, was best predicted by the body part of the stimulus when the chimeras were formed from familiar exemplars. Spatial frequency analysis of the stimuli showed that the body parts were richer in high spatial frequencies than the head parts, so these data are consistent with the hypothesis that categorization is more dependent on local stimulus features in pigeons than in humans. There was no corresponding trend when the chimeras were formed from novel exemplars. In Experiment 2, when morphs of training stimuli were used, response rates declined smoothly as the proportion of the morph contributed by the positive stimulus fell, although results with morphs of novel stimuli were again less orderly.     

Prior knowledge and subtyping effects in children's category learning

Two experiments examined how 5- and 10-year-old children revise their category representations when exposed to exemplars that are congruent or incongruent with existing knowledge. During training children were presented with exemplars containing features that were congruent or incongruent with children's social stereotypes together with a stereotype-neutral feature. In the knowledge-subtyping condition this neutral feature predicted the stereotype-congruence of the other features. In the knowledge-standard condition the neutral feature was uncorrelated with stereotype-congruence. At test children made judgements about feature co-occurrence within the learned category. In each experiment these judgements were influenced by both stereotypical beliefs and exemplar observation. Stereotypical beliefs, however, had a greater influence on co-occurrence judgements in the knowledge-subtyping than in the standard conditions. In Experiment 2 these effects were shown to generalize to judgements about features that were not presented during training. These results challenge current models of knowledge-based categorization by showing that exemplar structure determines whether novel exemplar features are incorporated into category representations.     

Comparing Exemplar- and Rule-Based Theories of Categorization

ABSTRACT— We address whether human categorization behavior is based on abstracted rules or stored exemplars. Although predictions of both theories often mimic each other in many designs, they can be differentiated. Experimental data reviewed does not support either theory exclusively. We find participants use rules when the stimuli are confusable and exemplars when they are distinct. By drawing on the distinction between simple stimuli (such as lines of various lengths) and complex ones (such as words and objects), we offer a dynamic view of category learning. Initially, categorization is based on rules. During learning, suitable features for discriminating stimuli may be gradually learned. Then, stimuli can be stored as exemplars and used to categorize novel stimuli without recourse to rules.