Decision rules in the perception and categorization of multidimensional stimuli.

This article examines decision processes in the perception and categorization of stimuli constructed from one or more components. First, a general perceptual theory is used to formally characterize large classes of existing decision models according to the type of decision boundary they predict in a multidimensional perceptual space. A new experimental paradigm is developed that makes it possible to accurately estimate a subject's decision boundary in a categorization task. Three experiments using this paradigm are reported. Three conclusions stand out: (a) Subjects adopted deterministic decision rules, that is, for a given location in the perceptual space, most subjects always gave the same response; (b) subjects used decision rules that were nearly optimal; and (c) the only constraint on the type of decision bound that subjects used was the amount of cognitive capacity it required to implement. Subjects were not constrained to make independent decisions on each component or to attend to the distance to each prototype. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotional response categorization.

Traditional theories of categorization in which categories are assumed to be grounded in perceptual similarity or theories ignore an important basis of conceptual structure: the emotion that a stimulus elicits in a perceiver. This article discusses the nature of, constraints on, and conditions of use of emotional response categories. Experiments in which participants sorted triads of concepts that shared both emotional and nonemotional relations indicate that individuals use emotional response categories when they are experiencing emotional states. Multidimensional scaling of similarity judgments by emotional and nonemotional perceivers supports a selective attention mechanism of these effects. Participants induced to feel happy or sad emotional states weighted the emotional responses associated with stimuli more heavily than people in relatively neutral states. The triad and multidimensional scaling findings, along with functional considerations, suggest that emotional response categorization is not only tenable, but necessary for a complete account of categorization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adaptive categorization in unsupervised learning.

In 3 experiments, the authors provide evidence for a distinct category-invention process in unsupervised (discovery) learning and set forth a method for observing and investigating that process. In the 1st 2 experiments, the sequencing of unlabeled training instances strongly affected participants' ability to discover patterns (categories) across those instances. In the 3rd experiment, providing diagnostic labels helped participants discover categories and improved learning even for instance sequences that were unlearnable in the earlier experiments. These results are incompatible with models that assume that people learn by incrementally tracking correlations between individual features; instead, they suggest that learners in this study used expectation failure as a trigger to invent distinct categories to represent patterns in the stimuli. The results are explained in terms of J. R. Anderson's (1990, 1991) rational model of categorization, and extensions of this analysis for real-world learning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context-gated knowledge partitioning in categorization.

According to the knowledge partitioning framework, people sometimes master complex tasks by creating multiple independent parcels of partial knowledge. Research has shown that knowledge parcels may contain mutually contradictory information, and that each parcel may be used without regard to knowledge that is demonstrably present in other parcels. This article reports 4 experiments that investigated knowledge partitioning in categorization. When component boundaries of a complex categorization were identified by a context cue, a significant proportion of participants learned partial and independent categorization strategies that were chosen on the basis of context. For those participants, a strategy used in one context was unaffected by knowledge demonstrably present in other contexts, suggesting that knowledge partitioning in categorization can be complete. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Irrelevant information in probabilistic categorization.

Using a probabilistic category learning paradigm, 6 experiments explored irrelevant information and 4 current models. Utilization of relevant configural information was lowered by the presence of an irrelevant dimension, both if that was the only relevant information and if a dimension was also relevant. An irrelevant cue value lowered the utilization of relevant cue values. An additional relevant dimension had a larger degrading effect on the utilization of a relevant dimension than an additional irrelevant dimension, thereby suggesting that the effect of irrelevant information is due to the complexity of the environment rather than to factors particular to the irrelevant nature of the information. The current models failed to fit the findings. However, results showing that memory errors account for salience effects provide a direction for revising one of the models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Racism and racial categorization.

Social identity theory predicts that perceivers strongly identified with an in-group will maximize the distinction and maintain a clear boundary between their own and other groups by categorizing others' membership accurately. Two experiments tested the prediction that racially prejudiced individuals, who presumably identify highly with their racial in-group, are more motivated to make accurate racial categorizations than nonprejudiced individuals. Results indicated that prejudiced participants not only took longer to categorize race-ambiguous targets (Experiments 1 and 2), but also made more nonverbal vocalizations when presented with them (Experiment 1), suggesting response hesitation. The results support the hypothesis that, compared to nonprejudiced individuals, prejudiced individuals concern themselves with accurate identification of in-group and out-group members and use caution when making racial categorizations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suboptimality in human categorization and identification.

Categorization and identification decision processes were examined and compared in 4 separate experiments. In all tasks, the critical stimulus component was a line that varied across trials in length and orientation, and the optimal decision rules were always complex piecewise quadratic functions. Evidence was found that identification is mediated by separate explicit and implicit systems. In addition, a common type suboptimality was found in both categorization and identification. In particular, observers apparently approximated the piecewise quadratic functions of the optimal decision rules with simpler piecewise linear functions. A computational model, which was motivated by a recent neuropsychological theory of category learning, successfully accounted for this suboptimal performance in both categorization and identification. The model assigns a key role to the striatum and assumes the observed suboptimality was largely due to massive convergence of visual cortical cells onto single striatal units. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prototype effects in categorization by pigeons.

In 4 experiments involving a total of 78 pigeons, Ss received a categorization task involving 6 simultaneous compounds in which the elements A, B, and C were more frequently paired with food than were the elements D, E, and F. Food was delivered after compounds ABF, AEC, and DBC but not after DEC, DBF, and AEF. Subsequent testing revealed a higher rate of responding during ABC than during any of the compounds that had signaled food and a lower rate of responding during DEF than during any of the compounds that had not signaled food. Exps 2, 3, and 4 further demonstrated that the rate of responding during test trials with ABC was faster than during a compound composed of 3 elements that had individually been paired with food. Results are more consistent with a configural than an elemental analysis of discrimination and categorization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychiatric diagnosis as prototype categorization.

Most critiques of the psychiatric diagnostic system seem to presuppose a "classical" view of categorization; an alternative view of categorization, frequently called the "prototype" view, is emerging in the psychological literature. The present article represents an attempt to apply this alternative view to psychiatric diagnosis. The central thesis is that while clinical diagnosis may appear "messy" and disordered from the classical perspective, it seems orderly and principled from the perspective of the prototype view. Two empirical investigations were conducted to document the utility of a change in views about psychiatric categorization systems and rules as they are used in practice, not with systems and rules that appear in the diagnostic manuals. The 1st investigation concerned the content and structure of the clinical features that trained psychiatrists commonly associate with patients from 9 different diagnostic categories. The 2nd investigation was concerned with problems of reliability and confidence in clinical diagnostic judgments. Results of both investigations provide support for the utility of the prototype view in this domain. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Velocity-based motion categorization by pigeons.

To examine if animals could learn action-like categorizations in a manner similar to noun-based categories, eight pigeons were trained to categorize rates of object motion. Testing 40 different objects in a go/no-go discrimination, pigeons were first trained to discriminate between fast and slow rates of object rotation around their central y-axis. They easily learned this velocity discrimination and transferred it to novel objects and rates. This discrimination also transferred to novel types of motions including the other two axes of rotation and two new translations around the display. Comparable tests with rapid and slow changes in the objects' size, color, and shape failed to support comparable transfer. This difference in discrimination transfer between motion-based and property-based changes suggests the pigeons had learned motion concept rather than one based on change per se. The results provide evidence that pigeons can acquire an understanding of motion-based actions, at least with regard to the property of object velocity. This may be similar to our use of verbs and adverbs to categorize different classes of behavior or motion (e.g., walking, jogging, or running slow vs. fast). (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Information-accumulation theory of speeded categorization.

A process model of perceptual categorization is presented, in which it is assumed that the earliest stages of categorization involve gradual accumulation of information about object features. The model provides a joint account of categorization choice proportions and response times by assuming that the probability that the information-accumulation process stops at a given time after stimulus presentation is a function of the stimulus information that has been acquired. The model provides an accurate account of categorization response times for integral-dimension stimuli and for separable-dimension stimuli, and it also explains effects of response deadlines and exemplar frequency. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cue abstraction and exemplar memory in categorization.

In this article, the authors compare 3 generic models of the cognitive processes in a categorization task. The cue abstraction model implies abstraction in training of explicit cue-criterion relations that are mentally integrated to form a judgment, the lexicographic heuristic uses only the most valid cue, and the exemplar-based model relies on retrieval of exemplars. The results from 2 experiments showed that, in lieu of the lexicographic heuristic, most participants spontaneously integrate cues. In contrast to single-system views, exemplar memory appeared to dominate when the feedback was poor, but when the feedback was rich enough to allow the participants to discern the task structure, it was exploited for abstraction of explicit cue-criterion relations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exemplar effects in categorization and multiple-cue judgment.

Categorization and multiple-cue judgment are similar tasks, but the influential models in the two areas are different in terms of the computations, processes, and neural substrates that they imply. In categorization, exemplar memory is often emphasized, whereas multiple-cue judgment generally is interpreted in terms of integration of Cues that have been abstracted in training. In 3 experiments the authors investigated whether these conclusions derive from genuine differences in the processes or are accidental to the different research methods. The results revealed large individual differences and a shift from exemplar memory to cue abstraction when the criterion is changed from a binary to a continuous variable, especially for a probabilistic criterion. People appear to switch between qualitatively distinct processes in the 2 tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Feature and rule selection in categorization tasks.

The process by which stimuli are assigned to categories has been traditionally conceptualized as bottom-up. Accordingly, stimulus features are supposed to be the fundamental units of analysis, and categorization to be accomplished on the basis of feature category correlations (cue validities). Alternatively, top-down processes are invoked, in which case one begins with a given categorization rule and then assigns stimuli to categories on that basis. Bottom-up and top-down views share a fundamental weakness, namely, they are unable to specify how features or rules, respectively, are acquired. This difficulty can be overcome if it is assumed that the process starts with neither features nor rules, but with stimuli. Then, as a result of experience with stimuli belonging to different categories, the cognitive system discovers and uses locally constructed features that maximally discriminate between the categories at hand. According to this view, the relationship between a target and a contrast category is the main factor affecting what subjects learn about each. Two experiments were conducted to explore this hypothesis. Both experiments support the notion that the relationship between the target and contrast category significantly determines which critical features are extracted as being defining of either category. In particular, it determines the level of generality of these features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Causal status and coherence in causal-based categorization.

Research has documented two effects of interfeature causal knowledge on classification. A causal status effect occurs when features that are causes are more important to category membership than their effects. A coherence effect occurs when combinations of features that are consistent with causal laws provide additional evidence of category membership. In this study, we found that stronger causal relations led to a weaker causal status effect and a stronger coherence effect (Experiment 1), that weaker alternative causes led to stronger causal status and coherence effects (Experiment 2), and that “essentialized” categories led to a stronger causal status effect (Experiment 3), albeit only for probabilistic causal links (Experiment 4). In addition, the causal status effect was mediated by features' subjective category validity, the probability they occur in category members. These findings were consistent with a generative model of categorization but inconsistent with an alternative model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The time course of categorization.

The extended generalized context model (EGCM) is presented as a formal model of the time course of categorization of complex stimuli. The model explains the effects of time constraints on categorization. The EGCM accurately accounts for existing data on categorization under time pressure. The model was tested further in 2 experiments. In both experiments, processing time in a perceptual categorization task was restricted by unpredictable peremptory response signals. In Experiment 1, restrictions of processing time had systematic effects on response proportions, and these effects were well explained by the EGCM. Experiment 2 showed that perceptual salience and utility have independent effects on the time course of categorization, as predicted by the EGCM. The EGCM's relation to other models of the time course of categorization is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decoupling object detection and categorization.

We investigated whether there exists a behavioral dependency between object detection and categorization. Previous work (Grill-Spector & Kanwisher, 2005) suggests that object detection and basic-level categorization may be the very same perceptual mechanism: As objects are parsed from the background they are categorized at the basic level. In the current study, we decouple object detection from categorization by manipulating the between-category contrast of the categorization decision. With a superordinate-level contrast with people as one of the target categories (e.g., cars vs. people), which replicates Grill-Spector and Kanwisher, we found that success at object detection depended on success at basic-level categorization and vice versa. But with a basic-level contrast (e.g., cars vs. boats) or superordinate-level contrast without people as a target category (e.g., dog vs. boat), success at object detection did not depend on success at basic-level categorization. Successful object detection could occur without successful basic-level categorization. Object detection and basic-level categorization do not seem to occur within the same early stage of visual processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)