Cognitive Psychology

Previous research has indicated that decision making is accompanied by an increase in the coherence of assessments of the factors related to the decision alternatives. In the present study, the authors investigated whether this coherence shift is obtained before people commit to a decision, and whether it is obtained in the course of a number of other processing tasks. College students were presented with a complex legal case involving multiple conflicting arguments. Participants rated agreement with the individual arguments in isolation before seeing the case and after processing it under various initial sets, including playing the role of a judge assigned to decide the case. Coherence shifts were observed when participants were instructed to delay making the decision (Experiment 1), to memorize the case (Experiment 2), and to comprehend the case (Experiment 3). The findings support the hypothesis that a coherence-generating mechanism operates in a variety of processing tasks, including decision making.

Theories of analogical reasoning have assumed that a 1-to-1 constraint discourages reasoners from mapping a single element in 1 analog to multiple elements in another. Empirical evidence suggests that reasoners sometimes appear to violate the 1-to-1 constraint when asked to generate mappings, yet virtually never violate it when asked to generate analogical inferences. However, few studies have examined analogical inferences based on nonisomorphic analogs, and their conclusions are suspect due to methodological problems. We sought to elicit mixed inferences that could result from combining information from 2 possible mappings. Participants generated 2-to-1 correspondences when asked for explicit mappings, but did not produce mixed inferences. Multiple correspondences appear to arise from multiple isomorphic mappings, rather than from a single homomorphic mapping.

We present a Bayesian model of causal learning that incorporates generic priors on distributions of weights representing potential powers to either produce or prevent an effect. These generic priors favor necessary and sufficient causes. Across three experiments, the model explains the systematic pattern of human judgments observed for questions regarding support for a causal link, for both generative and preventive causes.

Computational models of analogy have assumed that the strength of an inductive inference about the target is based directly on similarity of the analogs and in particular on shared higher order relations. In contrast, work in philosophy of science suggests that analogical inference is also guided by causal models of the source and target. In 3 experiments, the authors explored the possibility that people may use causal models to assess the strength of analogical inferences. Experiments 1-2 showed that reducing analogical overlap by eliminating a shared causal relation (a preventive cause present in the source) from the target increased inductive strength even though it decreased similarity of the analogs. These findings were extended in Experiment 3 to cross-domain analogical inferences based on correspondences between higher order causal relations. Analogical inference appears to be mediated by building and then running a causal model. The implications of the present findings for theories of both analogy and causal inference are discussed.

Because youth with aggressive conduct disorder (CD) often inflict pain on others, it is important to determine if they exhibit atypical empathic responses to viewing others in pain. In this initial functional magnetic resonance imaging (fMRI) study, 8 adolescents with aggressive CD and 8 matched controls were scanned while watching animated visual stimuli depicting other people experiencing pain or not experiencing pain. Furthermore, these situations involved either an individual whose pain was caused by accident or an individual whose pain was inflicted on purpose by another person. After scanning, participants rated how painful the situations were. In both groups the perception of others in pain was associated with activation of the pain matrix, including the ACC, insula, somatosensory cortex, supplementary motor area and periaqueductal gray. The pain matrix was activated to a significantly greater extent in participants with CD, who also showed strong amygdala, ventral striatum, and temporal pole activation. When watching situations in which pain was intentionally inflicted, control youth also exhibited signal increase in the medial prefrontal frontal cortex, lateral obitofrontal cortex, and temporoparietal junction, whereas youth with CD only exhibited activation in the insula. Furthermore, connectivity analyses demonstrated that youth with CD exhibited less amygdala/prefrontal coupling when watching pain inflicted by another than did control youth. These preliminary findings suggest that youth with aggressive CD exhibit an atypical pattern of neural response to viewing others in pain that should be explored in further studies.

The lateral posterior nucleus and pulvinar (LP-pulvinar complex) are the principal thalamic nuclei associated with the elaborate development of the dorsal and ventral streams of the parietal cortex in primates. In humans, a novel site of origin for a subpopulation of pulvinar neurons has been observed, the ganglionic eminence of the telencephalon. This additional site of neuron origin has been proposed to contribute to the pulvinar's evolutionary expansion Nat Neurosci 4:930 -936). Studies of neuron number in the LP-pulvinar complex in gibbon, chimpanzee, and gorilla compared to humans, however, did not show that the human LPpulvinar was unexpectedly large (Armstrong [1981] Am J Phys Anthropol 55:369 -383). Here we enlarge the allometric basis for comparison by determining neuron number in the LP-pulvinar complex of six New World primates (Cebus apella, Saimiri ustius, Saguinus midas niger, Alouatta caraya, Aotus azarae, and Callicebus moloch) as well as measuring LP-pulvinar volume in a further set of 24 species including additional primates, carnivores, and rodents. The volume of the LP-pulvinar complex scaled with positive allometry with respect to brain volume across all species examined. The scaling of the number of neurons in the LP-pulvinar complex was extremely similar in New World primates and anthropoid apes, with the human LP-pulvinar value close to the regression line. Comparison of the relative volumes of the LP-pulvinar in the larger sample confirmed this observation, and further demonstrated that both primates and carnivores showed a "grade shift" in its size compared to rodents, with the pulvinar comprising a greater proportion of total brain volume across the board. Diurnal, nocturnal, or crepuscular niche did not discriminate LP-pulvinar size across taxa.

Designing auditory displays requires understanding how different attributes of sound are processed. Operators must often listen to a particular stimulus dimension and make control actions contingent on the auditory information. Three experiments used a selective-listening paradigm to examine interactions between auditory dimensions. Participants were instructed to attend to either relative pitch or direction of pitch change of dynamic stimuli. With vertically arranged keypress responses, reactions to both dimensions showed stimulus-response compatibility effects, indicating that pitch is treated spatially. Direction of pitch change affected responses to pitch; level of pitch more strongly affected responses to pitch change. To reduce deleterious effects of irrelevant pitch information, auditory display designers can restrict the pitch range used to display dynamic data.

Designing auditory displays requires understanding how different attributes of sound are processed. Operators must often listen to a particular stimulus dimension and make control actions contingent on the auditory information. Three experiments used a selective-listening paradigm to examine interactions between auditory dimensions. Participants were instructed to attend to either relative pitch or direction of pitch change of dynamic stimuli. With vertically arranged keypress responses, reactions to both dimensions showed stimulus-response compatibility effects, indicating that pitch is treated spatially. Direction of pitch change affected responses to pitch; level of pitch more strongly affected responses to pitch change. To reduce deleterious effects of irrelevant pitch information, auditory display designers can restrict the pitch range used to display dynamic data.

Research on auditory graphs has investigated mappings, scalings, and polarities , as well as the addition of some contextual design features , in order to improve performance. However, little has been done to quantify the performance effects of such features, or to investigate effects of training in specific sonification tasks such as point estimation. Smith and Walker took a step towards quantifying and comparing the effects of adding several contextual design features. Presented here are selected results from a comprehensive follow-on study comparing effects of adding auditory context, either with or without training. The overall results indicate that some kinds of auditory context improved performance, while others did not. Training improved performance, and an interaction was discovered between type of auditory context and type of training . Implications are discussed.

Museums, science centers, zoos and aquaria are faced with educating and entertaining an increasingly diverse visitor population with varying physical and sensory needs. There are very few guidelines to help these facilities develop non-visual exhibit information, especially for dynamic exhibits. In an effort to make such informal learning environments (ILEs) more accessible to visually impaired visitors, the Georgia Tech Accessible Aquarium Project is studying auditory display and sonification methods for use in exhibit interpretation. The work presented here represents the initial tool building stage. We discuss the sonification system we are developing, and present some examples of the soundscape implementations that have been produced so far.

Two eye-movement experiments examined the processing of sentences containing reduced relative constructions. In the first experiment, animacy of the sentential subject, structural ambiguity, and parafoveal preview of syntactically disambiguating material were manipulated. Evidence of disruption was found in temporarily ambiguous sentences, regardless of animacy or preview. In the second experiment, readers with high versus low verbal working memory capacity read the sentences from Experiment 1. High and low-span readers exhibited very similar patterns of processing. As in the first experiment, evidence for disruption was found in temporarily ambiguous sentences whether the sentential subject was animate or inanimate. Sentences with animate subjects were hard to interpret, and relatively late measures of processing indicated that an animate subject made ambiguity especially hard to overcome. We interpret the findings as being consistent with serial, depth-first models of parsing.

One way young children could learn words is by pairing spoken words with co-occurring possible referents in the extralinguistic environment, collecting multiple such pairs, and then figuring out the common elements by cross-situational observation. In this account, the word-to-world mapping problem might be solved by computing distributional statistics across words, across referents, and most importantly across the co-occurrences of these two. As a first step in providing detailed experimental evidence for such mechanism, we briefly exposed adults to a set of trials wherein multiple spoken words and multiple pictures of individual objects co-occur in each learning situation with no information about the correspondences. The results show that they were able to learn the correct pairings in different highly ambiguous learning conditions. Moreover, we propose and implement a computational model and feed it with the same training data used in different learning conditions in experimental studies, to shed light on the possible underlying mechanism of statistical learning.

Problem-based learning (PBL) is a constructivist pedagogy in which students learn science and develop critical thinking skills by solving real-world problems in small groups. Studies have shown that PBL students are more motivated and become better learners. However, this pedagogy places additional demands on faculty. It takes time and expertise to develop suitable problems, to coach students, and to facilitate problem-solving sessions. We are developing interactive computer systems incorporating the PBL approach which (1) help teachers design, enter, and share problems, and (2) support students and guide them through the PBL inquiry process and (3) assist teachers to continue their professional development by improving their domain knowledge. System development is guided by K-16 educators and tested in classrooms. Our goal is to enable educators to adopt this pedagogy in K-16 classrooms with minimal overhead and to assist them to effortlessly learn new technologies and new material.

When designing research to examine the variables underlying creative thinking and problem solving success, one must not only consider (a) the demands of the task being performed, but (b) the characteristics of the individual performing the task and (c) the constraints of the skill execution environment. In the current paper we describe methodologies that allow one to eVectively study creative thinking by capturing interactions among the individual, task, and problem solving situation. In doing so, we demonstrate that the relation between executive functioning and problem solving success is not always as straightforward as one might initially believe.

We examined whether individual differences in working memory influence the facility with which individuals learn new categories. Participants learned two different types of category structures: rule-based and information-integration. Successful learning of the former category structure is thought to be based on explicit hypothesis testing that relies heavily on working memory. Successful learning of the latter category structure is believed to be driven by procedural learning processes that operate largely outside of conscious control. Consistent with a widespread literature touting the positive benefits of working memory and attentional control, the higher one's working memory, the fewer trials one took to learn rule-based categories. The opposite occurred for information-integration categories -the lower one's working memory, the fewer trials one took to learn this category structure. Thus, the positive relation commonly seen between individual differences in working memory and performance can not only be absent, but reversed. As such, a comprehensive understanding of skill learning -and category learning in particular -requires considering the demands of the tasks being performed and the cognitive abilities of the performer.

The techniques of computer vision have reached excellent results when applied in the different areas. These methods are used in the discovery of knowledge from images of the real world. This project aims to apply these techniques in morphometric analysis of biological species, trying to classify them. The morphometric analysis makes the extraction of measures in the most diverse structures, such as animals living organs, fruits, leaves, etc.. The development of the project was divided into three parts: (i) study and implementation of the techniques of computer vision (signatures, Fourier transform and curvature), (ii) analysis and extraction of characteristics of the biological images, (iii) classification of species through the techniques of pattern recognition (classification by minimum distance method). The results showed that the techniques of computer vision can be satisfactorily applied in the classification of biological species, which were able to classify correctly 81.82% of the species.

Prinz (Perceptual the Mind: Concepts and Their Perceptual Basis, MIT Press, 2002) presents a new species of concept empiricism, under which concepts are off-line long-term memory networks of representations that are 'copies' of perceptual representationsproxytypes. An apparent obstacle to any such empiricism is the prevailing nativism of generative linguistics. The paper critically assesses Prinz's attempt to overcome this obstacle. The paper argues that, prima facie, proxytypes are as incapable of accounting for the structure of the linguistic mind as are the more traditional species of empiricism. This position is then confirmed by looking in detail at two suggestions (one derived from recent connectionist research) from Prinz of how certain aspects of syntactic structure might be accommodated by the proxytype theory. It is shown that the suggestions fail to come to terms with both the data and theory of contemporary linguistics.

The anterior cingulate cortex presumptively regulates blood pressure reactions to behavioral stressors. There is little evidence in humans, however, that stressor-evoked changes in blood pressure correlate with concurrent changes in anterior cingulate activity. Using fMRI, we tested whether changes in mean arterial blood pressure correlate with ongoing changes in blood oxygen level dependent (BOLD) activation in 9 women and 11 men who completed a stressful Stroop color-word interference task. Higher mean arterial pressure during the Stroop task correlated with greater BOLD activation in two regions of the cingulate cortex (perigenual and mid-anterior) and in other networked brain regions, including the insula, thalamus, and periaqueductal gray. These results support the hypothesis that the anterior cingulate cortex regulates blood pressure reactions to behavioral stressors in humans.

The application of functional imaging to study visceral sensation has generated considerable interest regarding insight into the function of the brain-gut axis. Brain activation in normal control subjects during visceral sensation includes the perigenual cingulate cortex, which is involved in affective processing and has direct connections to autonomic centers. In contrast, somatic pain rarely activates the perigenual cingulate. This difference in brain activation is highly interpretable because visceral stimuli are experienced as more unpleasant than somatic stimuli. Clinical studies are suggestive of functional changes that may be a consequence or cause of conditions such as irritable bowel syndrome, but the findings are not consistent and are not as obviously interpretable as the differences observed when contrasting visceral and somatic stimulation. Although this is partly because brain imaging is still a relatively new technique, it also reflects weaknesses inherent to the understanding of chronic visceral pain as a biopsychosocial phenomenon. The biopsychosocial concept is very broad and rarely provides for precise predictions or mechanisms that can be directly tested using brain imaging. Future use of brain imaging to examine chronic visceral pain and other pain disorders will be more likely to succeed by describing clear theoretical and clinical endpoints.

Previous research suggested that older adults have a specific impairment in remembering verbal associative information, but it is unclear how elaboration and familiarity might influence this deficit in situations that involve perceptual processing. In the present experiments, younger and older participants studied male-female pairs of faces. Participants were then administered an associative recognition test consisting of previously studied pairs, pairs that contained previously studied items that were not studied together (i.e., conjunction pairs), and entirely new pairs of faces, and participants were instructed to identify pairs that had been presented together at study. Overall, participants were successful at recognizing previously presented pairs but were highly likely to mistakenly endorse conjunction pairs. This pattern was more pronounced for older adults, especially when items were repeated at encoding. Such data suggest that memory for face pairs relies largely on the familiarity of each face and not on a more precise recollection of associative information.

The present study examined how younger and older adults remember price information. Participants studied grocery items that were priced at market value or were well above or below market value. Although younger adults displayed better recall performance for unrealistic prices than older adults, there was no age difference for realistic prices, and both groups were equally accurate at remembering the general price range of the items. The results suggest that when older adults can rely on prior knowledge and schematic support, and tasks involve naturalistic materials, memory for associative information can be as good as that of younger adults.

Number symbols are part of our everyday visual world. Here we show that merely looking at numbers causes a shift in covert attention to the left or right side, depending upon the number's magnitude. This observation implies obligatory activation of number meaning and signals a tight coupling of internal and external representations of space.

Why do we remember some events and not others, and how does this change in old age? Although there are a variety of ways to address this question, the present perspective emphasizes how value can have a profound eVect on how we use our memory to remember certain information. The ability to select and prioritize what information is important to remember, relative to less salient or peripheral information, is an essential skill for the eYcient use of memory. For example, university students seek to memorize information they think is important for a later test, while grandparents may focus on being able to remember information about children and grandchildren, as well as important life events. In both cases, value is used to direct resources toward information that is deemed to be important to remember. The role that value plays in memory performance is critical to develop a comprehensive understanding of how memory is used across the adult life span.

A growing methodology, known as the systems factorial technology (SFT), is being developed to diagnose the types of information-processing architectures (serial, parallel, or coactive) and stopping rules (exhaustive or self-terminating) that operate in tasks of multidimensional perception. Whereas most previous applications of SFT have been in domains of simple detection and visual-memory search, this research extends the applications to foundational issues in multidimensional classification. Experiments are conducted in which subjects are required to classify objects into a conjunctive-rule category structure. In one case the stimuli vary along highly separable dimensions, whereas in another case they vary along integral dimensions. For the separable-dimension stimuli, the SFT methodology revealed a serial or parallel architecture with an exhaustive stopping rule. By contrast, for the integral-dimension stimuli, the SFT methodology provided clear evidence of coactivation. The research provides a validation of the SFT in the domain of classification and adds to the list of converging operations for distinguishing between separable-dimension and integral-dimension interactions. 1 The SFT methodology can also be used to diagnose another aspect of information-processing architecture, namely, capacity. For example, in a limited-capacity parallel-processing architecture, the rate at which information is gathered along each individual processing channel is reduced as the total number of processing channels increases. We do not investigate issues involving capacity in the present research, however.

Observers were presented with pairs of objects varying along binary-valued attributes and learned to predict which member of each pair had a greater value on a continuously varying criterion variable. The predictions from exemplar models of categorization were contrasted with classic alternative models, including generalized versions of a "take-the-best" model and a weighted-additive model, by testing structures in which interactions between attributes predicted the magnitude of the criterion variable. Under typical training conditions, observers showed little sensitivity to the attribute interactions, thereby challenging the predictions from the exemplar models. In a condition involving highly extended training, observers eventually learned the relations between the attribute interactions and the criterion variable. However, an analysis of the observers' response times for making their paired-comparison decisions also challenged the exemplar model predictions. Instead, it appeared that most observers recoded the interacting attributes into emergent configural cues. They then applied a set of hierarchically organized rules based on the priority of the cues to make their decisions.

The authors develop and test generalized versions of take-the-best (TTB) and rational (RAT) models of multiattribute paired-comparison inference. The generalized models make allowances for subjective attribute weighting, probabilistic orders of attribute inspection, and noisy decision making. A key new test involves a response-time (RT) approach. TTB predicts that RT is determined solely by the expected time required to locate the 1st discriminating attribute, whereas RAT predicts that RT is determined by the difference in summed evidence between the 2 alternatives. Critical test pairs are used that partially decouple these 2 factors. Under conditions in which ideal observer TTB and RAT strategies yield equivalent decisions, both the RT results and the estimated attribute weights suggest that the vast majority of subjects adopted the generalized TTB strategy. The RT approach is also validated in an experimental condition in which use of a RAT strategy is essentially forced upon subjects.

Speeded perceptual classification experiments were conducted to distinguish among the predictions of exemplar-retrieval, decision-boundary, and prototype models. The key manipulation was that across conditions, individual stimuli received either probabilistic or deterministic category feedback. Regardless of the probabilistic feedback, however, an ideal observer would always classify the stimuli by using an identical linear decision boundary. Subjects classified the probabilistic stimuli with lower accuracy and longer response times than they classified the deterministic stimuli. These results are in accord with the predictions of the exemplar model and challenge the predictions of the prototype and decision-boundary models.

Multidimensional scaling (MDS) techniques provide a promising measurement strategy for characterizing individual differences in cognitive processing, which many clinical theories associate with the development, maintenance, and treatment of psychopathology. The authors describe the use of deterministic and probabilistic MDS techniques for investigating numerous aspects of perceptual organization, such as dimensional attention, perceptual correlation, within-attribute organization, and perceptual variability. Additionally, they discuss how formal quantitative models can be used, in conjunction with MDS-derived representations of individual differences in perceptual organization, to test theories about the role of cognitive processing in clinically relevant phenomena. They include applied examples from their work in the areas of eating disorders and sexual coercion.

found that an exemplar similarity model provided better accounts of individual subject classification and generalization performance than did a mixed prototype model proposed by . However, these previous tests used a nonlinearly separable category structure. In the present work, the authors extend the previous findings by demonstrating a superiority for the exemplar generalization model over the mixed prototype model in a case involving a linearly separable structure. Because this structure has numerous features that Minda and Smith argued should be conducive to prototype-based processing, the results pose a significant challenge to the mixed prototype view.

Experiments were conducted in which observers learned to classify simple perceptual stimuli into low-variability and high-variability categories. Similarities between objects were measured in independent psychological-scaling tasks. The results showed that observers classified transfer stimuli into the high-variability categories with greater probability than was predicted by a baseline version of an exemplar-similarity model. Qualitative evidence for the role of category variability on perceptual classification, which could not be explained in terms of the baseline exemplar-similarity model, was obtained as well. Possible accounts of the effects of category variability are considered in the General Discussion section.

R. M. Nosofsky and T. J. Palmeri's (1997) exemplar-based random-walk (EBRW) model of speeded classification is extended to account for speeded same-different judgments among integral-dimension stimuli. According to the model, an important component process of same-different judgments is that people store individual examples of experienced same and different pairs of objects in memory. These exemplar pairs are retrieved from memory on the basis of how similar they are to a currendy presented pair of objects. The retrieved pairs drive a random-walk process for making same-different decisions. The EBRW predicts correctly that same responses are faster for objects lying in isolated than in dense regions of similarity space. The model also predicts correctly effects of same-identity versus samecategory instructions and is sensitive to observers' past experiences with specific same and different pairs of objects.

The authors propose and test an exemplar-based random walk model for predicting response times in tasks of speeded, multidimensional perceptual classification. The model combines elements of R.M. Nosofsky's (1986) generalized context model of categorization and G. D. instance-based model of automaticity. In the model, exemplars race among one another to be retrieved from memory, with rates determined by their similarity to test items. The retrieved exemplars provide incremental information that enters into a random walk process for making classification decisions. The model predicts correctly effects of within-and between-categories similarity, individual-object familiarity, and extended practice on classification response times. It also builds bridges between the domains of categorization and automaticity.

The authors compared the exemplar-based random-walk (EBRW) model of and the decision-bound model (DBM) of on their ability to predict performance in Garner's (1974) speeded classification tasks. A key question was the extent to which the models could predict facilitation in the correlated task and interference in the filtering task, in situations involving integral-dimension stimuli. To obtain rigorous constraints for model evaluation, the goal was to fit the detailed structure of the response time (RT) distribution data associated with each individual stimulus in each task. Both models yielded reasonably good global quantitative fits to the RT distribution and accuracy data. However, the DBM failed to properly characterize the interference effects in the filtering task. Apparently, a fundamental limitation of the DBM is that it predicts that the fastest RTs in the filtering task should be faster than the fastest RTs in the control task, whereas the opposite pattern was observed in our data.

Nosofsky and Palmeri (in press) proposed and tested an exemplarbased random walk model for predicting response times in tasks of speeded multidimensional perceptual classification. According to the model, test items serve as retrieval cues for category exemplars stored in memory. The exemplars race to be retrieved with rates determined by their similarity to the presented items. The retrieved exemplars then provide information that enters into a random walk process. In this chapter, after first reviewing the model, I present tests of its ability to fit categorization response-time distributions. I also explore extensions of the model designed to account for unidimensional absolute judgment and category same-different judgment.

Classification experiments were designed to compare the predictions of a linear decision bound model with those of an exemplar-similarity model incorporating an explicit selective attention mechanism. Linear boundaries could account for the data only in tasks involving separable dimension stimuli and where the boundary separating the categories was orthogonal to the psychological dimensions. Linear boundaries provided poor fits to the classification data in situations involving integral dimensions or when the boundary needed to be oriented in oblique directions in the space. The results were consistent with the selection-attention assumptions embodied in the exemplar model. It was argued that similar assumptions about selective attention need to be incorporated within decision bound models.

A formal proof is pnnided that Anderson's {1990) rational model of categorization generalizes the Medin and Schaffer {1978) context model. According to the context model, people represent categ<>ries by storing individual exemplars in memoiy. According to the rational mode!, people represent categories in terms of midtiple exemplarclusters or prototypes. In both models, a multiplicative rule is used to compute the similarity of an item to the underlying category representations. In certain special cases, each multiple prototype in the rational model corresponds to an individual exemplar, and in these cases the rational model reduces to the context model. Preliminary quantitative comparisons between the models are illustrated to test whether the multiple-prototype view adds significant explanatory power over the pure exemplar view.

A rule-instantiation model and a similarity-to-exemplars model were contrasted in terms of their predictions of typicality judgments and speeded classificalions-for-members-oflogically defined categories. In Experiment 1, subjects learned a unidimensional rule based on the size of objects. It was assumed that items that maximally instantiated the rule were those farthest from the category boundary that separated small and large stimuli. In Experiment 2, subjects learned a disjunctive rule ofthe form "x or y or both." It was assumed that items that maximally instantiated the rule were those with both positive values (x and y). In both experiments, the frequency with which different exemplars were presented during classification learning was manipulated across conditions. These frequency manipulations exerted a major impact on subjects' postacquisition goodness-of-example judgments, and they also influenced reaction times in a speeded classification task. The results could not be predicted solely on the basis of the degree to which the rules were instantiated. The goodnessjudgments were predicted fairly well by a mixed-exemplar model involving both relative-similarity and absolute-similarity components. It was concluded that even for logically defined concepts, stored exemplars may form a major component of the category representation.

Subjects learned to classify perceptual stimuli varying along continuous, separable dimensions into rule-described categories. The categories were designed to contrast the predictions of a selective-attention exemplar model and a simple rule-based model formalizing an economy-ofdescription view. Converging evidence about categorization strategies was obtained by also collecting identification and recognition data and by manipulating strategies via instructions. In free-strategy conditions, the exemplar model generally provided an accurate quantitative account of identification, categorization, and recognition performance, and it allowed for the interrelationship of these paradigms within a unified framework. Analyses of individual subject data also provided some evidence for the use of rules, but in general, the rules seemed to have a great deal in common with exemplar storage processes. Classification and recognition performance for subjects given explicit instructions to use specific rules contrasted dramatically with performance in the free-strategy conditions and could not be predicted by the exemplar model.

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.

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.

The multivariate theory of similarity discussed by Ennis (1988) 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.

The bow and sequential effects in absolute identification are investigated in this paper by following two strategies: (1)Experiments are performed in which sequential dependencies in signal presentations are manipulated, and (2)analyses are conducted (some of which are largely free of model-specific assumptions) which bear directly on the question of the origin of the sequential effects. The main result of the study is that absolute identification performance is greatly improved in a design in which each signal lies close to the preceding signal presented, even though the entire range of signals used is the same as in a random presentation design. This finding is consistent with the attention-band model of and rejects hypotheses that suggest that the variability in the signal representation in absolute identification is a function solely of the range of signals being used. However, nonparametric analyses of sequential response errors show that a plausible assumption concerning the trial. by-trial movement of the attention band provides an incomplete explanation of sequential effects in absolute identification. These results are far better explained in terms of systematic shifts of category boundaries in a Thurstonian model, as suggested by Purks, Callahan, Braida, and Durlach (1980). Experiments are also performed which suggest that memory decay is not the major factor accounting for the bow effect in absolute identification.

While it is well-known that faces provide linguistically relevant information during communication, most efforts to identify the visual correlates of the acoustic signal have focused on the shape, position and luminance of the oral aperture. In this work, we extend the analysis to full facial motion under the assumption that the process of producing speech acoustics generates linguistically salient visual information, which is distributed over large portions of the face. Support for this is drawn from our recent studies of the eye movements of perceivers during a variety of audiovisual speech perception tasks. These studies suggest that perceivers detect visual information at low spatial frequencies and that such information may not be restricted to the region of the oral aperture. Since the biomechanical linkage between the facial and vocal tract systems is one of close proximity and shared physiology, we propose that physiological models of speech and facial motion be integrated into one audiovisual model of speech production. In addition to providing a coherent account of audiovisual motor control, the proposed model could become a useful experimental tool, providing synthetic audiovisual stimuli with realistic control parameters.

In this chapter, I consider how objects might phenomenally look to beings with more coarse-grained visual systems than us. Many hold that to such beings, objects may phenomenally look red, without phenomenally looking a particular shade of red. David Armstrong expresses this intuition as follows: ‘It is perfectly possible… to have a mental image of a piece of crimson cloth of no particular shade of crimson.’ In this chapter I try to make intuitions of the kind that Armstrong has precise, and I try to make some progress towards evaluating them.