Exemplar-based accounts of relations between classification, recognition, and typicality.

Previously published sets of classification and old–new recognition memory data are reanalyzed within the framework of an exemplar-based generalization model. The key assumption in the model is that, whereas classification decisions are based on the similarity of a probe to exemplars of a target category relative to exemplars of contrast categories, recognition decisions are based on overall summed similarity of a probe to all exemplars. The summed-similarity decision rule is shown to be consistent with a wide variety of recognition memory data obtained in classification learning situations and may provide a unified approach to understanding relations between categorization and recognition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Storage and retrieval of associative clusters: A stages-of-learning analysis of associative memory traces.

In this research, the assumptions underlying the unitary trace theory of item representation and acquisition were tested in two cued-recall experiments in which the degree of preexperimental knowledge (typicality) was manipulated. Subjects learned lists of word triads (each of which consisted of a single cue and two targets) to a stringent acquisition criterion. In Experiment 1, typicality was manipulated in the absence of semantic relationships between members of the associative clusters. In Experiment 2, semantic relationships were present among cluster members, and preexperimental knowledge was manipulated by varying the degree of intracluster category membership as measured by whether cue and target items were typical or atypical category exemplars. In both experiments a mathematical model that embodies stages-of-learning distinctions was used to analyze the acquisition data. The results indicated that (1) cues and targets were represented in a single holistic memory trace, and (2) the manipulation of the degree of preexperimental knowledge affected both trace storage and retrieval learning, but had only a minimal impact on retrieval performance between the time a trace was stored and the time retrieval learning was complete. It was argued that these findings are consistent with a single unitary trace interpretation, namely, the modified storage-retrieval model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ideals and category typicality.

Barsalou (1985) argued that exemplars that serve category goals become more typical category members. Although this claim has received support, we investigated (a) whether categories have a single ideal, as negatively valenced categories (e.g., cigarette) often have conflicting goals, and (b) whether ideal items are in fact typical, as they often have unusual attributes. Because past studies on ideals were largely correlational and often used categories not strongly associated to goals (e.g., tree, bird, fish), we took an experimental approach, using categories with obvious goals. Our results indicated that exemplars having goal-fulfilling characteristics are generally judged as less typical than exemplars with average features. Also, although subjects had a general consensus on the ideals of neutral and positive categories, they held opposing opinions on the ideals of the negatively valenced categories. We found that this bimodality in idealness perception was due to differing perspectives taken on the categories; however, perspectives that changed idealness of category exemplars did not influence their typicality. In short, ideal exemplars that best serve category goals are not necessarily perceived as typical. We contrast the goal-fulfilling aspect of ideals with the structural notion of extreme values (e.g., very tall trees), which may influence typicality through other mechanisms. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Distinguishing prototype-based and exemplar-based processes in dot-pattern category learning.

The authors contrast exemplar-based and prototype-based processes in dot-pattern categorization. In Experiments 1A and 1B, participants provided similarity ratings of dot-distortion pairs that were distortions of the same originating prototype. The results show that comparisons to training exemplars surrounding the prototype create flat typicality gradients within a category and small prototype-enhancement effects, whereas comparisons to a prototype center create steep typicality gradients within a category and large prototype-enhancement effects. Thus, prototype and exemplar theories make different predictions regarding common versions of the dot-distortion task. Experiment 2 tested these different predictions by having participants learn dot-pattern categories. The steep typicality gradients, the large prototype effects, and the superior fit of prototype models suggest that participants refer to-be-categorized items to a representation near the category's center (the prototype), and not to the training exemplars that surround the prototype. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The contribution of category relationships to similarity ratings.

Two experiments with university students produced evidence that category relationships contribute to similarity ratings. In Exp 1, participants gave similarity ratings with respect to a semantic category (VEGETABLE) and a set of exemplars, some of which were members of the category (e.g., BROCCOLI) and some of which were not (e.g., BANANA). A regression analysis was used to predict the similarity ratings in terms of numbers of common and distinctive features, as reported by other participants. Perceived similarity was greater for exemplars that were members of the category, independently of feature overlap. Exp 2 examined similarity ratings with respect to pairs of exemplars. In some cases, both exemplars were members of the same category (e.g., BROCCOLI/CUCUMBER). In other cases, one exemplar was a member of the category and the other was not (e.g., BROCCOLI/BANANA). A regression analysis was used to predict the similarity ratings in terms of numbers of common and distinctive features. Perceived similarity was greater when both exemplars were members of the same category, independently of feature overlap. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An interactive activation approach to object processing: effects of structural similarity, name frequency, and task in normality and pathology

We present a computational model of the processes involved in retrieving stored semantic and name information from objects, using a simple interactive activation and competition architecture. We simulate evidence showing a cross-over in normal reaction times to make semantic classification and identification responses to objects from categories with either structurally similar or structurally dissimilar exemplars, and that identification times to objects from these two different classes correlate differentially with measures of the structural similarity of objects within the category and the frequency of the object's name. Structural similarity exerts a negative effect on object decision as well as naming, though this effect is larger on naming. Also, on naming, structural similarity interacts with the effects of name frequency, captured in the model by varying the weight on connections from semantic to name units; frequency effects are larger with structurally dissimilar items. In addition, (1) the range of potential errors for objects from these two classes, when responses are elicited before activation reached a stable state, differ--a wider range of errors occur to objects from categories with structurally similar exemplars; and (2) simulated lesions to different locations within the model produce selective impairments to identification but not to semantic classification responses to objects from categories with structurally similar exemplars. We discuss the results in relation to data on visual object processing in both normality and pathology.     

Learning of ill-defined categories by monkeys.

Three rhesus monkeys were trained on a categorization task using a successive-discrimination paradigm. The category members were geometric stimuli differing in color, form, size, and orientation; and the component features of category exemplars were neither singly necessary nor jointly sufficient to determine category membership. Original learning was followed by transfer tests involving both training stimuli and new exemplars. After this initial learning and transfer phase, the assignment of categories to positional responses was reversed. After the reversal learning criterion was met, transfer tests were again given. This procedure was continued until 5 reversals had been completed. Ss were able to learn this task involving ill-defined categories and showed both appropriate transfer to new examples and improvement across successive reversals. Both the learning and transfer data are in accord with the idea that component features are encoded or combined in an interactive, rather than an independent, manner and show parallels with human classification data. (French abstract) (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

By land or by sea: The role of perceptual similarity in infants' categorization of animals.

In 3 experiments, the authors used an object-examining task to investigate the role of perceptual similarity in infants' categorization. In Experiment 1, infants were familiarized with a set of either perceptually similar or perceptually variable exemplars from 1 category and tested with novel exemplars from both categories. Ten-month-olds did not respond to the category in either condition, and 13-month-olds responded categorically in both conditions but somewhat differently in the 2 conditions. Experiment 2 showed that when 10-month-olds were familiarized with similar exemplars but not with variable exemplars, they responded to the categorical distinction when given tests with typical exemplars. Experiment 3 established that 10-month-olds could differentiate among the exemplars. These results suggest that the perceptual similarity of the exemplars influences infants' recognition of categorical distinctions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prototype abstraction by monkeys (Macaca mulatta).

The authors analyze the shape categorization of rhesus monkeys (Macaca mulatta) and the role of prototype- and exemplar-based comparison processes in monkeys' category learning. Prototype and exemplar theories make contrasting predictions regarding performance on the Posner-Homa dot-distortion categorization task. Prototype theory--which presumes that participants refer to-be-categorized items to a representation near the category's center (the prototype)--predicts steep typicality gradients and large prototype-enhancement effects. Exemplar theory--which presumes that participants refer to-be-categorized items to memorized training exemplars-predicts flat typicality gradients and small prototype-enhancement effects. Across many categorization tasks that, for the first time, assayed monkeys' dot-distortion categorization, monkeys showed steep typicality gradients and large prototype-enhancement effects. These results suggest that monkeys--like humans--refer to-be-categorized items to a prototype-like representation near the category's center rather than to a set of memorized training exemplars. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inferring category attributes from exemplar attributes: Geometric shapes and social categories.

Three experiments tested the hypothesis that judgments about the attributes of categories are disproportionately based on the characteristics of exemplars that fit the category. In the first 2 experiments, subjects were presented with good and bad exemplars of categories with defining attributes (rectangles, triangles, pentagons, and ellipses) in which different colors were arbitrarily paired with the good and poor exemplars. In both experiments, subjects erroneously judged the colors paired with the good exemplars as more frequent than colors paired with the poor exemplars. A third experiment, using social categories, examined whether attributes associated with a single category member were more likely to generalize to the category as a whole for prototypical than for nonprototypical category members. Subjects were presented with information about individual fraternity members who varied in prototypicality, and the tendency to infer a target behavior (liberal vs. conservative voting behavior) from the individual fraternity member to the fraternity as a whole increased with the prototypicality of the category member. Implications for the contact hypothesis, category–exemplar relations, and belief stability are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Attention, similarity, and the identification–categorization relationship.

A unified quantitative approach to modeling Ss' identification and categorization of multidimensional perceptual stimuli is proposed and tested. Two Ss identified and categorized the same set of perceptually confusable stimuli varying on separable dimensions. The identification data were modeled using R. N. Shepard's (see record 1959-05134-001) multidimensional scaling-choice framework, which was then extended to model the Ss' categorization performance. The categorization model, which generalizes the context theory of classification developed by D. L. Medin and M. M. Schaffer (see record 1979-12633-001), assumes that Ss 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 2 paradigms. Findings provide some support for the hypothesis that Ss distribute attention among component dimensions so as to optimize categorization performance and that Ss may have augmented their category representations with inferred exemplars. Results demonstrate that excellent predictions of categorization performance can be made given knowledge of performance in an identification paradigm. (51 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facial expressions of emotion: Does the prototype represent central tendency, frequency of instantiation, or an ideal?

Examines whether typicality of facial expressions (FE) of emotion is predicted best by their values on an ideal dimension (suitability to express a particular emotion), their frequency of instantiation (FI) as an expression of a particular emotion, or their deviation from the central tendency (CT) of the respective FE category. The subjects (Ss) judged FE line drawings of anger, disgust, happiness, sadness, and surprise differing in intensity. In study 1, 82 Ss (mean age 24.4 yrs) divided into four independent groups were tested: the typicality group, the FI group, the ideal group, and the CT group. The Ss in Study 2 (mean age 23.5 yrs) sought to replicate Study 1 with a different operation of typicality: "how good an example" an FE is for the respective emotion category. The results strongly indicate that they are structured like goal-derived categories, where typicality of members varies according to their suitability to obtain a certain goal. This indicates that suitability to express the respective emotion is highly salient in people's representations of categories of FEs of emotion and has become the standard by which typicality is judged. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of artificial categories structured by family resemblances: A comparative study in people (Homo sapiens) and pigeons (Columba livia).

Adult humans (Homo sapiens) and pigeons (Columba livia) were trained to discriminate artificial categories that the authors created by mimicking 2 properties of natural categories. One was a family resemblance relationship: The highly variable exemplars, including those that did not have features in common, were structured by a similarity network with the features correlating to one another in each category. The other was a polymorphous rule: No single feature was essential for distinguishing the categories, and all the features overlapped between the categories. Pigeons learned the categories with ease and then showed a prototype effect in accord with the degrees of family resemblance for novel stimuli. Some evidence was also observed for interactive effects of learning of individual exemplars and feature frequencies. Humans had difficulty in learning the categories. The participants who learned the categories generally responded to novel stimuli in an all-or-none fashion on the basis of their acquired classification decision rules. The processes that underlie the classification performances of the 2 species are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inference and Classification Learning of Abstract Coherent Categories.

Category learning research has primarily focused on how people learn to classify items using simple observable features. However, classification is only 1 way to learn categories. In addition, many concepts have an underlying coherence that explains the featural similarity among exemplars, such as abstract coherent concepts whose instances differ greatly on their observable features. In 3 experiments, the authors investigated how abstract coherent categories are acquired through 2 common means of category learning, classification and inference. Because inference promotes more focus on within-category information than does classification, they hypothesized that inference learning would lead to a better understanding of the underlying coherence of abstract coherent categories. All 3 experiments support this prediction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for intact semantic representations in patients with frontal lobe lesions.

Patients with frontal lobe lesions and control participants were assessed on 2 tests of semantic knowledge. In the triadic comparison task, participants were shown all possible triplets of 12 animal names and judged which 2 of each triplet were most alike. In the ordered similarity task, participants rank ordered animals in terms of their similarity to a target animal. For both tasks, semantic structure-- derived from multidimensional scaling techniques-- revealed similar representations in patients with frontal lobe lesions and control participants. Additional pathfinder analyses also produced networks that did not differ between groups. These patients exhibited intact semantic knowledge despite deficits on tests of free recall and verbal fluency that involved the same semantic category and exemplars. Thus, intact representation of semantic knowledge in frontal patients stands in contrast to their marked deficits in strategic retrieval of semantic knowledge. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Automatic semantic priming: Effect of category exemplar level and word association level.

Evaluated semantic priming when the prime was masked below naming threshold and the target was named in 4 experiments with 263 undergraduates. Exp I showed that when word primes were masked and word targets were named, prior knowledge of the related pairs did not alter semantic priming. Semantic priming within categories occurred only when the prime stimulus was the 1st category exemplar. Findings of Exp II indicate that when masked pictures were used as primes, semantic priming for word targets was sensitive to the category exemplar level of the prime but not to the category exemplar level of the target. Word association norms collected in Exp III did not support the hypothesis that the effect of category exemplar level was mediated by the strength of word association. Exp IV revealed significant semantic priming for masked picture primes and within-category word targets, regardless of the level of word association between prime and target. Exp IV also demonstrated semantic priming for high word association targets that were not members of the same semantic category. For all experiments, Ss with the longest average reaction times (RTs) also showed the largest semantic priming effect for naming word targets. It is suggested that viewing one of the highest ranking category exemplars activates the memory representation of the category, perhaps because such prototypic exemplars are contained within the category concept itself. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relational similarity and context effects in category verification.

Two experiments with a total of 50 undergraduate and graduate students measured the effects of coordinate falses, which pair 2 exemplars from a common category (e.g., "A dog is a cat"), on latencies to true items in a category verification task. Results show that although, relative to anomalous falses, coordinate falses did not increase latencies to trues, the size of the increase did not vary with the similarity of the coordinates. Furthermore, latencies were faster to coordinate falses that were more similar than to coordinate falses that were less similar. These results suggest relational similarity is as powerful a predictor of performance in category verification as is attribute similarity. Finally, there was some evidence that the increase in latencies was the same for typical and atypical category exemplars. It is concluded that this last finding, if substantiated, indicates that relational information is generally accessed prior to attribute information. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Direct and indirect tests of memory for category exemplars in young and older adults.

Young and older adults were compared on direct (cued recall) and indirect (exemplar generation) tests of memory for category members. Because category names served as cues in both tasks, amount of retrieval support was constant across tasks. Although older adults produced fewer category members in cued recall, priming of category exemplars in the generation task did not vary with age. These results suggest that age constancy in priming tasks does not depend on physical similarity between study materials and retrieval cues provided at test and point to the importance of deliberate recollection as a factor in determining the extent of age differences in memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The out-group must not be so bad after all: The effects of disclosure, typicality, and salience on intergroup bias.

Two contact studies integrated the personalization (M. B. Brewer & N. Miller, 1994) and category-based models (M. Hewstone & R. J. Brown, 1986), proposing that greater reduction of intergroup bias can be achieved by the interactive effects of disclosure and typicality (Study 1) or disclosure and salience (Study 2). In Study 1 the impact of self-disclosure and typicality combined interactively to augment intergroup acceptance. Study 2 extended these findings by examining the combined effects of disclosure and category salience. It also explored the mediational roles of group-relevant and person-relevant information on the effects of typicality and disclosure, respectively. Results showed that during cooperative dyadic out-group contact, self-disclosure, typicality, and salience were key factors for reducing bias toward new members of that out-group category. (PsycINFO Database Record (c) 2010 APA, all rights reserved)