Exemplar similarity and the development of automaticity

Effects of exemplar similarity on the development of automaticity were investigated with a task in which participants judged the numerosity of random patterns of between 6 and 11 dots. After several days of training, response times were the same at all levels of numerosity, signaling the development of automaticity. In Experiment 1, response times to new patterns were a function of their similarity to old patterns. In Experiment 2, responses to patterns with high within-category similarity became automatized more quickly than responses to patterns with low within-category similarity. In Experiment 3, responses to patterns with high between-category similarity became automatized more slowly than responses to patterns with low between-category similarity. A new theory, the exemplar-based random walk (EBRW) model, was used to explain the results. Combining elements of G. D. Logan's (1988) instance theory of automaticity and R. M. Nosofsky's (1986) generalized context model of categorization, the theory embeds a dynamic similarity-based memory retrieval mechanism within a competitive random walk decision process.     

Similarity, frequency, and category representations.

This article studies the joint roles of similarity and frequency in determining graded category structure. Perceptual classification learning experiments were conducted in which presentation frequencies of individual exemplars were manipulated. The exemplars had varying degrees of similarity to members of the target and contrast categories. Classification accuracy and typicality ratings increased for exemplars presented with high frequency and for members of the target category that were similar to the high-frequency exemplars. Typicality decreased for members of the contrast category that were similar to the high-frequency exemplars. A frequency-sensitive similarity-to-exemplars model provided a good quantitative account of the classification learning and typicality data. The interactive relations among similarity, frequency, and categorization are considered in the General Discussion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

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)     

Attention and learning processes in the identification and categorization of integral stimuli.

Studied the relationship between identification and categorization learning of integral-dimension stimuli within the framework of an exemplar-based generalization model. The model was used to predict learning in 6 different categorization conditions on the basis of data obtained in a single identification learning condition. 34 undergraduates were tested in the identification learning condition and 191 undergraduates were tested in the categorization learning conditions. An assumption in the model is that because of selective attention to component dimensions, similarity relations may change in systematic ways across different experimental contexts. Results indicate that selective attention may play a critical role in determining the identification–categorization relationship for integral stimuli. Similarity among exemplars decreased as a function of identification learning. It is noted that alternative classification models, including prototype, multiple-prototype, average distance, and value-on-dimensions models, were unable to account for the results. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response-time tests of logical-rule models of categorization.

A recent resurgence in logical-rule theories of categorization has motivated the development of a class of models that predict not only choice probabilities but also categorization response times (RTs; Fifi?, Little, & Nosofsky, 2010). The new models combine mental-architecture and random-walk approaches within an integrated framework and predict detailed RT-distribution data at the level of individual participants and individual stimuli. To date, however, tests of the models have been limited to validation tests in which participants were provided with explicit instructions to adopt particular processing strategies for implementing the rules. In the present research, we test conditions in which categories are learned via induction over training exemplars and in which participants are free to adopt whatever classification strategy they choose. In addition, we explore how variations in stimulus formats, involving either spatially separated or overlapping dimensions, influence processing modes in rule-based classification tasks. In conditions involving spatially separated dimensions, strong evidence is obtained for application of logical-rule strategies operating in a serial-self-terminating processing mode. In conditions involving spatially overlapping dimensions, preliminary evidence is obtained that a mixture of serial and parallel processing underlies the application of rule-based classification strategies. The logical-rule models fare considerably better than major extant alternative models in accounting for the categorization RTs. (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.     

On exemplar-based exemplar representations: Reply to Ennis (1988).

The multivariate theory of similarity discussed by D. M. Ennis (see record 1989-14369-001) entails the assumption that individual category exemplars are themselves represented psychologically as distributions of individual exemplars. The potential utility of this exemplar-distribution approach for theories relating selective attention, similarity, and categorization is briefly discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Roles of function, reminding, and variability in categorization by 3-month-old infants.

The roles of function, reminding, and exemplar variability in categorization of a physically dissimilar object were studied with 3-month-old infants trained to move a crib mobile by kicking. Performance on a transfer test with a motionless novel object provided evidence of categorization. In Experiments 1 and 2, infants, like adults, initially categorized novel objects on the basis of physical appearance, but only if trained with multiple exemplars, after delays of 1 and 7 days. In Experiment 3, prior knowledge of an object's functional properties overrode physical dissimilarity as the basis for categorization and enabled reminding of the classification response 2 weeks later. In Experiment 4, postevent contingency information overrode physical and functional properties as the basis for categorization. These findings indicate that expectations and goals influence infants' category decisions and raise the possibility that infants of 3 months respond by analogy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory storage and retrieval processes in category learning.

Studied the detailed course of learning for categorization tasks defined by independent or contingent probability distributions over the features of category exemplars in 2 experiments with 72 college-age Ss. Ss 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. 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. (46 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)     

Straight talk about linear separability.

It is intuitive that prototypes and additive similarity calculations might underlie human categorization, promoting a special appreciation of linearly separable categories. The failure to document empirically this appreciation has helped focus interest instead on exemplar strategies, multiplicative similarity calculations, and theory-based categorization. However, existing studies have mainly sampled poorly differentiated categories with small exemplar sets. Therefore, the present research repeated existing studies on linear separability, using better differentiated categories better stocked with exemplars. Both the data patterns and modeling suggest that prototypes and a linear separability constraint may have a stronger influence on categorization for these alternative category structures. The information processing basis for this result is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorizing chairs and naming pears: category differences in object processing as a function of task and priming

Four experiments are reported examining the locus of structural similarity effects in picture recognition and naming with normal subjects. Subjects carried out superordinate categorization and naming tasks with picture and word forms of clothing, furniture, fruit, and vegetable exemplars. The main findings were as follows: (1) Responses to pictures of fruit and vegetables ("structurally similar" objects) were slowed relative to pictures of clothing and furniture ("structurally dissimilar" objects). This structural similarity difference was greater for picture naming than for superordinate categorization of pictures. (2) Structural similarity effects in picture naming were reduced by repetition priming. Repetition priming effects were equivalent from picture and word naming as prime tasks. (3) However, superordinate categorization of the prime did not produce the structural similarity effects on priming found for picture naming. Furthermore, such priming effects did not arise for picture or word categorization or for reading picture names as target tasks. It is proposed that structural similarity effects on priming object processing are located in processes mapping semantic representations of pictures to name representations required to select names for objects. Visually based competition between fruit and vegetables produces competition in name selection, which is reduced by priming the mappings between semantic and name representations.     

Decision boundaries in one-dimensional categorization.

Decision-boundary theories of categorization are often difficult to distinguish from exemplar based theories of categorization. The authors developed a version of the decision-boundary theory, called the single-cutoff model, that can be distinguished from the exemplar theory. The authors present 2 experiments that test this decision-boundary model. The results of both experiments point strongly to the absence of single cutoffs in most participants, and no participant displayed use of the optimal boundary. The range of nonoptimal solutions shown by individual participants was accounted for by an exemplar-based adaptive-learning model. When combined with the results of previous research, this suggests that a comprehensive model of categorization must involve both rules and exemplars, and possibly other representations as well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alternative strategies of categorization

Psychological studies of categorization often assume that all concepts are of the same general kind, and are operated on by the same kind of categorization process. In this paper, we argue against this unitary view, and for the existence of qualitatively different categorization processes. In particular, we focus on the distinction between categorizing an item by: (a) applying a category-defining rule to the item vs. (b) determining the similarity of that item to remembered exemplars of a category. We begin by characterizing rule application and similarity computations as strategies of categorization. Next, we review experimental studies that have used artificial categories and shown that differences in instructions or time pressure can lead to either rule-based categorization or similarity-based categorization. Then we consider studies that have used natural concepts and again demonstrated that categorization can be done by either rule application or similarity calculations. Lastly, we take up evidence from cognitive neuroscience relevant to the rule vs. similarity issue. There is some indirect evidence from brain-damaged patients for neurological differences between categorization based on rules vs. that based on similarity (with the former involving frontal regions, and the latter relying more on posterior areas). For more direct evidence, we present the results of a recent neuroimaging experiment, which indicates that different neural circuits are involved when people categorize items on the basis of a rule as compared with when they categorize the same items on the basis of similarity.     

Global similarity predicts dissociation of classification and recognition: Evidence questioning the implicit–explicit learning distinction in amnesia.

Dissociation of classification and recognition in amnesia is widely taken to imply 2 functional systems: an implicit procedural-learning system that is spared in amnesia and an explicit episodic-learning system that is compromised. We argue that both tasks reflect the global similarity of probes to memory. In classification, subjects sort unstudied grammatical exemplars from lures, whereas in recognition, they sort studied grammatical exemplars from lures. Hence, global similarity is necessarily greater in recognition than in classification. Moreover, a grammatical exemplar's similarity to studied exemplars is a nonlinear function of the integrity of the data in memory. Assuming that data integrity is better for control subjects than for subjects with amnesia, the nonlinear relation combined with the advantage for recognition over classification predicts the dissociation of recognition and classification. To illustrate the dissociation of recognition and classification in healthy undergraduates, we manipulated study time to vary the integrity of the data in memory and brought the dissociation under experimental control. We argue that the dissociation reflects a general cost in memory rather than a selective impairment of separate procedural and episodic systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Short-term memory scanning viewed as exemplar-based categorization.

Exemplar-similarity models such as the exemplar-based random walk (EBRW) model (Nosofsky & Palmeri, 1997b) were designed to provide a formal account of multidimensional classification choice probabilities and response times (RTs). At the same time, a recurring theme has been to use exemplar models to account for old–new item recognition and to explain relations between classification and recognition. However, a major gap in research is that the models have not been tested on their ability to provide a theoretical account of RTs and other aspects of performance in the classic Sternberg (1966) short-term memory-scanning paradigm, perhaps the most venerable of all recognition-RT tasks. The present research fills that gap by demonstrating that the EBRW model accounts in natural fashion for a wide variety of phenomena involving diverse forms of short-term memory scanning. The upshot is that similar cognitive operating principles may underlie the domains of multidimensional classification and short-term old–new recognition. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Phonologically mediated access to meaning for Kanji: Is a rows still a rose in Japanese Kanji?

It is generally assumed that access to phonology for words written in logographic Japanese Kanji must be mediated by access to their meaning. This proposal was examined in a semantic categorization task with homophones. If the assumption about Kanji processing were true, then homophony should have no effect on semantic judgments. However, there was a significant homophone effect: Reaction times (RTs) were longer and more errors occurred to homophone foils than to control foils. There was also a significant effect of visual similarity: Incorrect target words that were visually similar to correct exemplars of the category names yielded longer RTs and higher error rates. The effects of both visual similarity and homophony were obtained even under conditions of pattern masking (though only on errors). The data suggest that the reading of Kanji is characterized by parallel access to semantics from orthographic and phonological representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comment on "Memory storage and retrieval processes in category learning."

Comments on a study by W. K. Estes (see record 1986-21175-001) that examined learning processes associated with categorization in relation to new–old recognition by focusing on alternative views of recognition/classification relations and the implications of the more detailed analyses of learning for exemplar-based classification models. It is argued that strategies typically used by experimental participants and exemplar processing have some fundamental properties in common. This implies that a good fit to classification data by an exemplar model does not necessarily mean that performance is based on comparisons with remembered exemplars and suggests that abstract representations may not be different kinds of entities from the memory representation of a specific experience. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the Categorization of Admired and Disliked Exemplars of Admired and Disliked Racial Groups.

The present work examined the influence of affective fit in the racial categorization process. Study 1 tested whether famous exemplars of stigmatized and nonstigmatized racial groups are categorized by race at differential rates, depending on whether they are admired or disliked. Using an inverted-face paradigm, Study 2 examined whether racial categorization accuracy differs for admired and disliked exemplars of these groups. Study 3 examined the influence of collective self-esteem on Whites' tendency to differentially categorize admired and disliked Black and White exemplars. Last, Study 4 replicated the pattern of results found in the previous studies for White participants, making use of unknown exemplars about whom participants learned either positive or negative information prior to categorizing them. Taken together, the results suggested that phenotypically irrelevant affective information regarding exemplars and their social group memberships influences the racial categorization process. Implications for prejudice and stereotyping are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)