Divided attention, aging, and priming in exemplar generation and category verification

Transfer-appropriate processing theories differentiate between conceptual- and perceptual-priming tasks. The former are said to be influenced by the nature of processing engaged in at study, but not by changes in modality between study and test; the latter are sensitive to changes in format between study and test, but not to variations in the extent of semantic processing at study. In the present experiments, we examined the effects of divided attention and aging on priming in exemplar generation and category verification, two tasks that require access to semantic information at test. Manipulations of attention during encoding affected the extent of priming in exemplar generation, but not in category verification. Priming effects were similar in young and older adults in exemplar generation following study in both full and divided attention. Although older adults did not demonstrate priming in category verification in one experiment, no effects of age or divided attention were observed in a second experiment. In addition, priming in category verification was unaffected by varying the level of processing at encoding. However, the absence of levels-of-processing and attention effects in category verification does not signal that priming in this task has a perceptual basis; priming in category verification was insensitive to modality shifts between study and test. The implications of these findings for theories of priming and cognitive aging are considered.     

What some effects might not be: The time to verify membership in 'well-defined' categories

Armstrong, Gleitman, and Gleitman (1983) reported shorter categorization times for members of well-defined categories judged more typical. They concluded that these effects could not originate in a graded, similarity-based category representation and consequently that the typicality effects obtained with natural categories might not be indicative of such a structure either. In this article, we re-examine this conclusion, focusing first on the performance obtained with well-defined categories of different sizes. Only the larger categories used showed variations in typicality ratings and produced typicality effects on categorization times. However,multiple regression analyses showed the effects on categorization times to be better explained by a measure of associative strength, called category dominance. The range of various predictor variables was equated in a follow-up experiment involving large, natural, and well-defined categories. Results obtained with well-defined categories showed pronounced dominance effects when typicality was controlled, but no reliable typicality effect when category dominance and instance familiarity were controlled. Results were opposite for natural categories. By showing that well-defined categories fail to produce unbiased typicality effects, our results bring added support to the hypothesis that the effects obtained with natural categories originate in a graded, similarity-based category structure.     

Semantic memory retrieval: Deadlining the typicality effect

Corbett and Wickelgren (1978), employing a speed-accuracy tradeoff method for verifying category membership, found that while the estimated strength of the category-instance association was higher for category examples given more frequently as instances of the category (i.e. higher instance dominance), retrieval dynamics did not vary across levels of instance dominance. The Corbett and Wickelgren data challenged the claims of models of speeded sentence verification that postulated differences in the retrieval processes of high- and low-dominance category-instance associations (e.g. Smith, Shoben, & Rips, 1974). We argued that Corbett and Wickelgren very probably used category instances of debatable membership status in their low-instance dominance category examples, thus making it impossible to decide which responses to these items were correct. This, in turn, rendered their low-instance dominance data uninterpretable. Two partial replications of the Corbett and Wickelgren study were carried out, each with four subjects, and 10 variable lags between the stimulus presentation and the response signal. When care was taken that each category instance clearly belonged to its respective category, an estimate of the rate at which information accumulated towards its asymptote was greater for high-dominance, high-typicality items than for low-dominance, medium-typicality items. However, there were no dominance or typicality differences in the estimates of this asymptotic strength. In contrast, in the study in which low-dominance, low-typicality items were of questionable category membership, the results were similar to those obtained by Corbett and Wickelgren. These data support the idea that there is a continuous accumulation of information in the semantic memory sentence verification task.     

Refining the visual-cortical hypothesis in category learning

Participants produce steep typicality gradients and large prototype-enhancement effects in dot-distortion category tasks, showing that in these tasks to-be-categorized items are compared to a prototypical representation that is the central tendency of the participant’s exemplar experience. These prototype-abstraction processes have been ascribed to low-level mechanisms in primary visual cortex. Here we asked whether higher-level mechanisms in visual cortex can also sometimes support prototype abstraction. To do so, we compared dot-distortion performance when the stimuli were size constant (allowing some low-level repetition-familiarity to develop for similar shapes) or size variable (defeating repetition-familiarity effects). If prototype formation is only mediated by low-level mechanisms, stimulus-size variability should lessen prototype effects and flatten typicality gradients. Yet prototype effects and typicality gradients were the same under both conditions, whether participants learned the categories explicitly or implicitly and whether they received trial-by-trial reinforcement during transfer tests. These results broaden out the visual-cortical hypothesis because low-level visual areas, featuring retinotopic perceptual representations, would not support robust category learning or prototype-enhancement effects in an environment of pronounced variability in stimulus size. Therefore, higher-level cortical mechanisms evidently can also support prototype formation during categorization.     

Evidence for two kinds of low-typical instances in a categorization task

Three experiments examined the relationship between instance typicality and reaction time (RT) in a semantic categorization task. In all three experiments, first the instance was presented, and then the category. High-typicality high-imagery instances (e.g., robin) and lowtypicality low-imagery instances (e.g., grackle) were categorized faster than low-typicality highimagery instances (e.g., penguin). Instructing subjects to generate images of the instances had no influence on the pattern of results. The difference in categorization RT for lowimagery low-typicality instances vs. high-imagery high-typicality instances suggests that these instances may be represented differently in memory.     

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.     

Associative and similarity-based processes in categorization decisions

Two experiments were directed at distinguishing associative and similarity-based accounts of systematic differences in categorization time for different items in natural categories. Experiment 1 investigated the correlation of categorization time with three measures of instance centrality in a category. Production frequency (PF), rated typicality, and familiarity from category norms for British participants (Hampton & Gardiner, 1983) were used to predict mean categorization times for 531 words in 12 semantic categories. PF and typicality (but not familiarity) were found to make significant and independent contributions to categorization time. Error rates were related only to typicality (apart from errors made to ambiguous or unknown items). Experiment 2 provided a further dissociation of PF and typicality. Manipulating the difficulty of the task through the relatedness of the false items interacted primarily with the effect of typicality on categorization time, whereas, under conditions of easy discrimination, prior exposure to the category exemplars affected only the contribution of PF to the decision time. The dissociation of typicality and PF measures is interpreted as providing evidence that speeded categorization involves both retrieval of associations indexed by PF and a similarity-based decision process indexed by typicality.     

German norms for semantic typicality, age of acquisition, and concept familiarity

The present study introduces the first substantial German database with norms for semantic typicality, age of acquisition, and concept familiarity for 824 exemplars of 11 semantic categories, including four natural (ANIMALS, BIRDS, FRUITS,: and VEGETABLES: ) and five man-made (CLOTHING, FURNITURE, VEHICLES, TOOLS: , and MUSICAL INSTRUMENTS: ) categories, as well as PROFESSIONS: and SPORTS: . Each category exemplar in the database was collected empirically in an exemplar generation study. For each category exemplar, norms for semantic typicality, estimated age of acquisition, and concept familiarity were gathered in three different rating studies. Reliability data and additional analyses on effects of semantic category and intercorrelations between age of acquisition, semantic typicality, concept familiarity, word length, and word frequency are provided. Overall, the data show high inter- and intrastudy reliabilities, providing a new resource tool for designing experiments with German word materials. The full database is available in the supplementary material of this file and also at www.psychonomic.org/archive .     

The role of graded category structure in imaginative thought

Participants generated lists of exemplars from the categories of animals, tools, and fruit, and their lists were used to determine the relative accessibility of individual exemplars. Measures of accessibility included output dominance (the number of participants who listed an exemplar), rank (how early instances were listed), and two scores that reflect their combination-output precedence and dominance/rank. Other participants drew and described novel exemplars of those categories that might exist on an imaginary planet and reported on the factors that influenced their creations. References to Earth animals, tools, or fruit were used to determine imagination frequency (the number of participants who mentioned relying on particular Earth exemplars). Items high in accessibility were also high in imagination frequency, implying that those items that come to mind most readily are the ones most likely to serve as starting points for the development of novel ideas. This result held even when task constraints weighed against the use of such items (Experiment 2) and when participants were encouraged to be as creative as possible (Experiment 4), suggesting that it is difficult to avoid the influence of highly accessible category exemplars. Other measures of category structure, including the rated typicality, familiarity, and frequency of exemplars, did not predict imagination frequency as well. The results are discussed in terms of expanding concept boundaries and the inadvertent application of knowledge that is readily accessible.     

Instance memorization and category influence: Challenging the evidence for multiple systems in category learning

A class of dual-system theories of categorization assumes a categorization system based on actively formed prototypes in addition to a separate instance memory system. It has been suggested that, because they have used poorly differentiated category structures (such as the influential “5-4” structure), studies supporting the alternative exemplar theory reveal little about the properties of the categorization system. Dual-system theories assume that the instance memory system only influences categorization behaviour via similarity to single isolated instances, without generalization across instances. However, we present the results of two experiments employing the 5-4 structure to argue against this. Experiment 1 contrasted learning in the standard 5-4 structure with learning in an even more poorly differentiated 5-4 structure. In Experiment 2, participants memorized the 5-4 structure based on a five minute simultaneous presentation of all nine category instances. Both experiments revealed category influences as reflected by differences in instance learnability and generalization, at variance with the dual-system prediction. These results have implications for the exemplars versus prototypes debate and the nature of human categorization mechanisms.     

Prior knowledge and cued recall: category size and dominance

Previous work indicates that our ability to recall a recently experienced word is reduced by the number of related concepts that it activates in permanent memory. The purpose of this research was to evaluate the possibility that dominance of primary associates, and not category size, is responsible for this observation. The results of three experiments involving manipulations of target and cue set size, as well as meaning and rhyme, indicate that category size effects are independent of dominance. In fact, the advantage of smaller categories and fewer activated items is substantially reduced for words having very dominant primary associates. The findings are discussed in relation to the Sensory-Semantic model.     

Classification response times in probabilistic rule-based category structures: Contrasting exemplar-retrieval and decision-boundary models

Experiments were conducted to contrast the predictions from exemplar models and rule-based decisionboundary models of perceptual classification. Observers classified multidimensional stimuli into categories that could be described in terms of easily verbalized logical rules. The critical manipulation was that some pairs of stimuli received probabilistic feedback, whereas other control pairs received deterministic feedback. Despite the probabilistic feedback, the probabilistic pairs and the deterministic pairs were the same distance from idealobserver, rule-based decision boundaries. Across two experiments with varying category structures, observers classified the probabilistic pairs with slower response times (RTs) and lower accuracies than the comparison deterministic pairs. The effects were relatively long term, extending into test blocks in which all feedback was withheld. The results were as predicted by exemplar models, but challenged models that posit that RT is a function solely of the distance of a stimulus from rule-based boundaries. The studies add considerable generality to previous ones and suggest that, even in domains involving rule-based category structures, exemplar-retrieval processes play a significant role. Supplemental materials related to this article may be downloaded from http:// mc.psychonomic-journals.org/content/supplemental.     

Prototypes in category learning: the effects of category size, category structure, and stimulus complexity

Although research in categorization has sometimes been motivated by prototype theory, recent studies have favored exemplar theory. However, some of these studies focused on small, poorly differentiated categories composed of simple, 4-dimensional stimuli. Some analyzed the aggregate data of entire groups. Some compared powerful multiplicative exemplar models to less powerful additive prototype models. Here, comparable prototype and exemplar models were fit to individual-participant data in 4 experiments that sampled category sets varying in size, level of category structure, and stimulus complexity (dimensionality). The prototype model always fit the observed data better than the exemplar model did. Prototype-based processes seemed especially relevant when participants learned categories that were larger or contained more complex stimuli.     

Solving anagrams: Category priming and the differential availability of category solutions

An experiment was performed to test the hypothesis that the effect of category name priming on anagram solving varies with the strength of the relationship between the solution word and the priming category. Subjects solved anagrams of taxonomic category instances under primed or unprimed conditions. In the primed condition, the name of the taxonomic category from which the solution word was chosen was provided on each trial. Priming was shown to facilitate anagram solution and the extent of this facilitation was directly related to the instance dominance of the solution word in the priming category. The results were discussed in terms of current models of semantic memory.     

Constraints on semantic priming in reading: A fixation time analysis

In Experiment 1, subjects read sentences containing a category name or a neutral prime that was followed by a target exemplar that varied in typicality. Fixation time on the target exemplar was the measure of processing difficulty. The category name facilitated processing for both high- and low-typicality exemplars. Unexpectedly, high-typicality exemplars were processed more quickly than low-typicality exemplars in both primed and unprimed conditions. Experiment 2 extended the priming effect to primary associates. Most importantly, the priming effect was influenced by the syntactic structure of the stimulus sentence. When both the prime and the associated target word were in the same clause, semantic priming occurred, but when the prime and target were in different clauses, no associative facilitation was observed. These results were interpreted as supporting a clausal processing hypothesis based on an autonomous modular view of the language processing system. Furthermore, the results were consistent with direct control models of eye movements, which claim that fixation duration reflects the timing of processing related to the word currently under fixation.     

Exemplar theory's predicted typicality gradient can be tested and disconfirmed

One of exemplar theory's central predictions concerns the shape of typicality gradients. The typicality gradient it predicts is a consequence of its exemplar–based comparisons and appears no matter how the theory is evaluated. However, this predicted typicality gradient does not fit the empirical typicality gradients obtained in an influential version of the dot–distortion category task, and this is true even when the exemplar model is made more flexible and mathematically powerful. Thus, exemplar theory is disconfirmed in this domain of categorization. In contrast, prototype theories are consistent with the empirically obtained typicality gradients.     

Effect of typicality on online category verification of animate category exemplars in aphasia

Normal young, elderly, Broca's aphasic, and Wernicke's aphasic individuals participated in an online category verification task where primes were superordinate category labels while targets were either typical or atypical examples of animate categories or nonmembers belonging to inanimate categories. The reaction time to judge whether the target belonged to the preceding category label was measured. Results indicated that all four groups made significantly greater errors on atypical examples compared to typical examples. Young and elderly individuals, and Broca's aphasic patients performed similarly on the verification task; these groups demonstrated faster reaction times on typical examples than atypical examples. Wernicke's aphasic patients made the most errors on the task and were slowest to respond than any other participant group. Also, these participants were not significantly faster at accepting correct typical examples compared to correct atypical examples. The results from the four groups are discussed with relevance to prototype/family resemblance models of typicality.     

Typicality aids search for an unspecified target,but only in identification and not in attentional guidance

Participants searched for a picture of an object, and the object was either a typical or an atypical category member. The object was cued by either the picture or its basic-level category name. Of greatest interest was whether it would be easier to search for typical objects than to search for atypical objects. The answer was “yes,” but only in a qualified sense: There was a large typicality effect on response time only for name cues, and almost none of the effect was found in the time to locate (i.e., first fixate) the target. Instead, typicality influenced verification time—the time to respond to the target once it was fixated. Typicality is thus apparently irrelevant when the target is well specified by a picture cue; even when the target is underspecified (as with a name cue), it does not aid attentional guidance, but only facilitates categorization.     

Effects of classification context on categorization in natural categories

The patterns of classification of borderline instances of eight common taxonomic categories were examined under three different instructional conditions to test two predictions: first, that lack of a specified context contributes to vagueness in categorization, and second, that altering the purpose of classification can lead to greater or lesser dependence on similarity in classification. The instructional conditions contrasted purely pragmatic with more technical/quasi-legal contexts as purposes for classification, and these were compared with a no-context control. The measures of category vagueness were between-subjects disagreement and within-subjects consistency, and the measures of similarity-based categorization were category breadth and the correlation of instance categorization probability with mean rated typicality, independently measured in a neutral context. Contrary to predictions, none of the measures of vagueness, reliability, category breadth, or correlation with typicality were generally affected by the instructional setting as a function of pragmatic versus technical purposes. Only one subcondition, in which a situational context was implied in addition to a purposive context, produced a significant change in categorization. Further experiments demonstrated that the effect of context was not increased when participants talked their way through the task, and that a technical context did not elicit more all-or-none categorization than did a pragmatic context. These findings place an important boundary condition on the effects of instructional context on conceptual categorization.