The sensitization and differentiation of dimensions during category learning.

The reported experiments explored 2 mechanisms by which object descriptions are flexibly adapted to support concept learning: selective attention and dimension differentiation. Arbitrary dimensions were created by blending photographs of faces in different proportions. Consistent with learned selective attention, positive transfer was found when initial and final categorizations shared either relevant or irrelevant dimensions. Unexpectedly good transfer was observed when both irrelevant dimensions became relevant and relevant dimensions became irrelevant, and was explained in terms of participants learning to isolate one dimension from another. This account was further supported by experiments indicating that conditions expected to produce positive transfer via dimension differentiation produced better transfer than conditions expected to produce positive transfer via selective attention, but only when stimuli were composed of highly integral and spatially overlapping dimensions.

Altering object representations through category learning.

Previous research has shown that objects that are grouped together in the same category become more similar to each other and that objects that are grouped in different categories become increasingly dissimilar, as measured by similarity ratings and psychophysical discriminations. These findings are consistent with two theories of the influence of concept learning on similarity. By a Strategic Judgment Bias account, the categories associated with objects are explicitly used as cues for determining similarity, and objects that are categorized together are judged to be more similar because similarity is not only a function of the objects themselves, but also the objects' category labels. By a Changed Object Description account, category learning alters the description of the objects themselves, emphasizing properties that are relevant for categorization. A new method for distinguishing between these accounts is introduced which measures the difference between the similarity ratings of categorized objects to a neutral object. The results indicate both strategic biases based on category labels and genuine representational change, with the strategic bias affecting mostly objects belonging to different categories and the representational change affecting mostly objects belonging to the same category.

The acquisition of automatic response biases through categorization.

Participants categorized left- and right-pointing line drawings presented together with pictures, whose pointing direction (to the left or right) was ambiguous (spatially ambiguous pictures; Experiments 1 and 2) or that pointed neither to the left nor to the right (spatially neutral pictures; Experiment 3). Subsequently, the spatially ambiguous and neutral pictures were used in a Simon task, wherein participants made left and right keypresses on the basis of the color of the pictures, while ignoring the object that they depicted. In all three experiments, performance was facilitated when the response required by the color matched the pointing direction of the line drawings with which the picture had been previously paired. Performance was impeded when the response required by the color did not match the pointing direction of the line drawings with which the picture had been previously paired. Thus, responses indirectly associated with pictures by category membership were automatically triggered even when the responses were inappropriate.

Unitization during category learning.

Five experiments explored the question of whether new perceptual units can be developed if they are useful for a category learning task, and if so, what the constraints on this unitization process are. During category learning, participants were required to attend either a single component or a conjunction of 5 components. Consistent with unitization, the conjunctive task became much easier with practice; this improvement was not found for the single-component task or for conjunctive tasks in which the components could not be unitized. Influences of component organization (Experiment 1), component contiguity (Experiment 2), component proximity (Experiment 3), and number of components (Experiment 4) on practice effects were found. Deconvolved response times (Experiment 5) showed that prolonged practice yielded faster responses than predicted by an analytic model that integrates evidence from independently perceived components.

Reuniting perception and conception.

Work in philosophy and psychology has argued for a dissociation between perceptually-based similarity and higher-level rules in conceptual thought. Although such a dissociation may be justified at times, our goal is to illustrate ways in which conceptual processing is grounded in perception, both for perceptual similarity and abstract rules. We discuss the advantages, power and influences of perceptually-based representations. First, many of the properties associated with amodal symbol systems can be achieved with perceptually-based systems as well (e.g. productivity). Second, relatively raw perceptual representations are powerful because they can implicitly represent properties in an analog fashion. Third, perception naturally provides impressions of overall similarity, exactly the type of similarity useful for establishing many common categories. Fourth, perceptual similarity is not static but becomes tuned over time to conceptual demands. Fifth, the original motivation or basis for sophisticated cognition is often less sophisticated perceptual similarity. Sixth, perceptual simulation occurs even in conceptual tasks that have no explicit perceptual demands. Parallels between perceptual and conceptual processes suggest that many mechanisms typically associated with abstract thought are also present in perception, and that perceptual processes provide useful mechanisms that may be co-opted by abstract thought.

Perceptual learning.

Perceptual learning involves relatively long-lasting changes to an organism's perceptual system that improve its ability to respond to its environment. Four mechanisms of perceptual learning are discussed: attention weighting, imprinting, differentiation, and unitization. By attention weighting, perception becomes adapted to tasks and environments by increasing the attention paid to important dimensions and features. By imprinting, receptors are developed that are specialized for stimuli or parts of stimuli. By differentiation, stimuli that were once indistinguishable become psychologically separated. By unitization, tasks that originally required detection of several parts are accomplished by detecting a single constructed unit representing a complex configuration. Research from cognitive psychology, psychophysics, neuroscience, expert/novice differences, development, computer science, and cross-cultural differences is described that relates to these mechanisms. The locus, limits, and applications of perceptual learning are also discussed.

The development of features in object concepts.

According to one productive and influential approach to cognition, categorization, object recognition, and higher level cognitive processes operate on a set of fixed features, which are the output of lower level perceptual processes. In many situations, however, it is the higher level cognitive process being executed that influences the lower level features that are created. Rather than viewing the repertoire of features as being fixed by low-level processes, we present a theory in which people create features to subserve the representation and categorization of objects. Two types of category learning should be distinguished. Fixed space category learning occurs when new categorizations are representable with the available feature set. Flexible space category learning occurs when new categorizations cannot be represented with the features available. Whether fixed or flexible, learning depends on the featural contrasts and similarities between the new category to be represented and the individuals existing concepts. Fixed feature approaches face one of two problems with tasks that call for new features: If the fixed features are fairly high level and directly useful for categorization, then they will not be flexible enough to represent all objects that might be relevant for a new task. If the fixed features are small, subsymbolic fragments (such as pixels), then regularities at the level of the functional features required to accomplish categorizations will not be captured by these primitives. We present evidence of flexible perceptual changes arising from category learning and theoretical arguments for the importance of this flexibility. We describe conditions that promote feature creation and argue against interpreting them in terms of fixed features. Finally, we discuss the implications of functional features for object categorization, conceptual development, chunking, constructive induction, and formal models of dimensionality reduction.

Similarity in context.

Similarity comparisons are highly sensitive to judgment context. Three experiments explore context effects that occur within a single comparison rather than across several trials. Experiment 1 shows reliable intransitivities in which a target is judged to be more similar to stimulus A than to stimulus B, more similar to B than to stimulus C, and more similar to C than to A. Experiment 2 explores the locus of Tversky's (1977) diagnosticity effect in which the relative similarity of two alternatives to a target is influenced by a third alternative. Experiment 3 demonstrates a new violation of choice independence which is explained by object dimensions' becoming foregrounded or backgrounded, depending upon the set of displayed objects. The observed violations of common assumptions to many models of similarity and choice can be accommodated in terms of a dynamic property-weighting process based on the variability and diagnosticity of dimensions.

Isolated and interrelated concepts.

A continuum between purely isolated and purely interrelated concepts is described. Along this continuum, a concept is interrelated to the extent that it is influenced by other concepts. Methods for manipulating and identifying a concept's degree of interrelatedness are introduced. Relatively isolated concepts can be empirically identified by a relatively large use of nondiagnostic features, and by better categorization performance for a concept's prototype than for a caricature of the concept. Relatively interrelated concepts can be identified by minimal use of nondiagnostic features, and by better categorization performance for a caricature than for a prototype. A concept is likely to be relatively isolated when subjects are instructed to create images for their concepts rather than find discriminating features, when concepts are given unrelated labels, and when the categories that are displayed alternate rarely between trials. The entire set of manipulations and measurements supports a graded distinction between isolated and interrelated concepts. The distinction is applied to current models of category learning, and a connectionist framework for interpreting the empirical results is presented.

Alignment-based nonmonotonicities in similarity.

According to the assumption of monotonicity in similarity judgments, adding a shared feature in common to 2 items should never decrease their similarity. Violations of monotonicity are not predicted by feature- or dimension-based models but can be accommodated by alignment-based models in which the parts of one compared display are placed in correspondence with the parts of the other display. In 2 experiments, evidence for nonmonotonicities is obtained that is generally consistent with the alignment-based model SIAM (similarity as interactive activation and mapping; R.L. Goldstone, 1994). The calculation of similarity in this model involves an interactive activation process whereby correspondences between the parts of compared displays mutually and concurrently influence each other. As SIAM predicts, the occurrence of nonmonotonicities depends on perceptual similarity of features and the duration of presented comparison.

Is adaptive coping possible for adult survivors of childhood sexual abuse?

Thirty adult women survivors of childhood sexual abuse who believed they were functioning well were selected through advertisements in local newspapers and presentations at an incest-survivor support group. Subjects were assessed by a battery of structured diagnostic interviews and standardized psychological measures, including the MMPI, the Trauma Symptom Checklist-40, and the Dissociative Experiences Scale. The results showed the existence of a subgroup of survivors of childhood sexual abuse who do not have devastating long-term psychological effects. Better adult psychological functioning was predicted by certain characteristics of the abuse, the family system, and the survivors.

Comparison and choice: Relations between similarity processes and decision processes.

Research and theory in decision making and in similarity judgment have developed along parallel paths. We review and analyze phenomena in both domains that suggest that similarity processing and decision making share important correspondences. The parallels are explored at the level of empirical generalizations and underlying processing principles. Important component processes that are shared by similarity judgments and decision making include generation of alternatives, recruitment of reference points, dynamic weighting of aspects, creation of new descriptors, development of correspondences between items, and justification of judgment. Preparation of this article was supported by National Science Foundation Grants 92-11277 and 91-10245.

The role of similarity in categorization: providing a groundwork.

The relation between similarity and categorization has recently come under scrutiny from several sectors. The issue provides an important inroad to questions about the contributions of high-level thought and lower-level perception in the development of people's concepts. Many psychological models base categorization on similarity, assuming that things belong in the same category because of their similarity. Empirical and in-principle arguments have recently raised objections to this connection, on the grounds that similarity is too unconstrained to provide an explanation of categorization, and similarity is not sufficiently sophisticated to ground most categories. Although these objections have merit, a reassessment of evidence indicates that similarity can be sufficiently constrained and sophisticated to provide at least a partial account of many categories. Principles are discussed for incorporating similarity into theories of category formation.

Patterns of recall of childhood sexual abuse as described by adult survivors.

Issues concerning the phenomenon of delayed recall of childhood trauma have arisen in forensic settings. For example, the courts have had to address the issue of delayed recall because of legislation extending the statute of limitations for bringing lawsuits related to childhood sexual abuse. Many states now allow victims to bring suit for up to three years after their memory returns. This paper describes patterns of recall of childhood sexual abuse as recounted by 30 adult women survivors in a nonforensic setting. Eleven of the women described remembering their childhood sexual abuse after a period of amnesia. Examples are given of the types of circumstances that were associated with the delayed recall of the abuse. Implications for assessment in clinical and forensic settings are discussed.

Relational similarity and the nonindependence of features in similarity judgments.

Four experiments examined the hypothesis that simple attributional features and relational features operate differently in the determination of similarity judgments. Forced choice similarity judgments ("Is X or Y more similar to Z?") and similarity rating tasks demonstrate that making the same featural change in two geometric stimuli unequally affects their judged similarity to a third stimulus (the comparison stimulus). More specifically, a featural change that causes stimuli to be more superficially similar and less relationally similar increases judged similarity if it occurs in stimuli that already share many superficial attributes, and decreases similarity if it occurs in stimuli that do not share as many superficial attributes. These results argue against an assumption of feature independence which asserts that the degree to which a feature shared by two objects affects similarity is independent of the other features shared by the objects. The MAX hypothesis is introduced, in which attributional and relational similarities are separately pooled, and shared features affect similarity more if the pool they are in is already relatively large. The results support claims that relations and attributes are psychologically distinct and that formal measures of similarity should not treat all types of matching features equally.