Evolution and devolution of folkbiological knowledge.

In this paper we present evidence in support of the hypothesis that the average person's knowledge about trees, and about the natural world in general, has declined during the 20th century. Our investigations are based on examination of a large sample of written material from the 16th through 20th centuries contained in the Oxford English Dictionary. In Analysis 1, we show a precipitous decline in the use of tree terms after, but not before, the 19th century. In Analysis 2, we analyze tree terms at different levels of organization and show that the decline observed in Analysis 1 occurs for all levels of organization. This second analysis also reveals that during the 16th to 19th centuries tree terms became progressively more specific, suggesting that during these periods knowledge about trees increased. In Analysis 3, we show similar rates of decline in other folkbiological categories, indicating that the change in tree terms reflects a general decline in knowledge about living kinds. Also in Analysis 3, we show that several non-biological categories have experienced evolution during the 20th century, indicating that the declines in the 20th century for folkbiological categories are not an inevitable outcome of the corpus. Finally, Analysis 4 also shows declines in the frequency of quotations for which the tree term was not the topic of the sentence, and thus incidental to the purposes of the writer. The results from Analysis 4 reassure us that the results from Analyses 1-3 were not solely due to change in the aims and purposes of writers over the centuries. In sum, the analyses indicate that in the domain of trees, there has been a long and sustained period of conceptual evolution followed by a recent pronounced period of devolution.

The role of covariation versus mechanism information in causal attribution.

Traditional approaches to causal attribution propose that information about covariation of factors is used to identify causes of events. In contrast, we present a series of studies showing that people seek out and prefer information about causal mechanisms rather than information about covariation. Experiments 1, 2 and 3 asked subjects to indicate the kind of information they would need for causal attribution. The subjects tended to seek out information that would provide evidence for or against hypotheses about underlying mechanisms. When asked to provide causes, the subjects' descriptions were also based on causal mechanisms. In Experiment 4, subjects received pieces of conflicting evidence matching in covariation values but differing in whether the evidence included some statement of a mechanism. The influence of evidence was significantly stronger when it included mechanism information. We conclude that people do not treat the task of causal attribution as one of identifying a novel causal relationship between arbitrary factors by relying solely on covariation information. Rather, people attempt to seek out causal mechanisms in developing a causal explanation for a specific event.

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

This article is based on the Estes (1986b) article that examined learning processes associated with categorization in relation to new-old recognition. The focus of the commentary is on alternative views of recognition/classification relations as well as the implications of the more detailed analyses of learning for exemplar-based classification models. The argument is made that strategies typically used by experimental participants and exemplar processing have some fundamental properties in common. This implies that a good fit to classification data by an exemplar model does not necessarily mean that performance is based on comparisons with remembered exemplars but suggests that abstract representations may not be different kinds of entities from the memory representation of a specific experience.

Problem structure and the use of base-rate information from experience.

This article is concerned with the use of base-rate information that is derived from experience in classifying examples of a category. The basic task involved simulated medical decision making in which participants learned to diagnose hypothetical diseases on the basis of symptom information. Alternative diseases differed in their relative frequency or base rates of occurrence. In five experiments initial learning was followed by a series of transfer tests designed to index the use of base-rate information. On these tests, patterns of symptoms were presented that suggested more than one disease and were therefore ambiguous. The alternative or candidate diseases on such tests could differ in their relative frequency of occurrence during learning. For example, a symptom might be presented that had appeared with both a relatively common and a relatively rare disease. If participants are using base-rate information appropriately (according to Bayes' theorem), then they should be more likely to predict that the common disease is present than that the rare disease is present on such ambiguous tests. Current classification models differ in their predictions concerning the use of base-rate information. For example, most prototype models imply an insensitivity to base-rate information, whereas many exemplar-based classification models predict appropriate use of base-rate information. The results reveal a consistent but complex pattern. Depending on the category structure and the nature of the ambiguous tests, participants use base-rate information appropriately, ignore base-rate information, or use base-rate information inappropriately (predict that the rare disease is more likely to be present). To our knowledge, no current categorization model predicts this pattern of results. To account for these results, a new model is described incorporating the ideas of property or symptom competition and context-sensitive retrieval.

Stimulus interaction and between-trials proactive interference in monkeys.

Most theoretical accounts of proactive interference in delayed-matching-to-sample paradigms focus on processes linked to time. Two experiments questioned this exclusive focus on temporal facts. Between-trials proactive interference was studied in a situation in which the similarity of consecutive trials was varied along the dimensions of color, form, and position. All of these factors as well as the similarity of sample and test contexts contributed to memory performance. A mathematical model based on the assumptions that similarity strongly influences memory-based judgements and that overall similarity is determined by the multiplicative interaction of component dimensions gave an excellent qualitative and quantitative account of the data in both experiments. These results support a broader view of factors determining proactive interference and are inconsistent with the idea that these multiple factors can be treated as independent.

Stimulus similarity and retroactive interference and facilitation in monkey short-term memory.

Four experiments examined the effects of similarity between the sample and an interpolated stimulus in a modified delayed-matching-to-sample (DMTS) paradigm. The basis trial sequence was as follows: (a) a sample was presented, and the response to it was either rewarded or nonrewarded, (b) an interpolated stimulus was presented, and the response to it was either rewarded or nonrewarded, and (c) after a delay interval a choice test was given between the initial sample and a new stimulus, with the sample being correct if it had been initially rewarded and incorrect if it had been initially nonrewarded. When the sample and the interpolated stimulus were associated with opposite outcomes (sample rewarded, interpolated stimulus not rewarded or sample not rewarded, interpolated stimulus rewarded), retroactive interference was observed to increase as the similarity of the two stimuli increased. When the two stimuli were either both rewarded or both nonrewarded, retroactive facilitation was observed so long as the sample and interpolated stimuli were similar along either the relevant or an irrelevant dimension. Finally, test probes involving the interpolated stimulus and a new stimulus revealed asymmetrical interactions such that the interpolated stimulus influenced performance on the initial stimulus more than the initial stimulus altered performance on the interpolated stimulus. Taken as a whole, the results are inconsistent with the idea that alternative stimuli are encoded independently of each other. At best, independence may hold only for cases in which the stimuli are not similar to each other.

Concepts and conceptual structure.

Research and theory on categorization and conceptual structure have recently undergone two major shifts. The first shift is from the assumption that concepts have defining properties (the classical view) to the idea that concept representations may be based on properties that are only characteristic or typical of category examples (the probabilistic view). Both the probabilistic view and the classical view assume that categorization is driven by similarity relations. A major problem with describing category structure in terms of similarity is that the notion of similarity is too unconstrained to give an account of conceptual coherence. The second major shift is from the idea that concepts are organized by similarity to the idea that concepts are organized around theories. In this article, the evidence and rationale associated with these shifts are described, and one means of integrating similarity-based and theory-driven categorization is outlined.

Expertise and category-based induction.

The authors examined inductive reasoning among experts in a domain. Three types of tree experts (landscapers, taxonomists, and parks maintenance personnel) completed 3 reasoning tasks. In Experiment 1, participants inferred which of 2 novel diseases would affect "more other kinds of trees" and provided justifications for their choices. In Experiment 2, the authors used modified instructions and asked which disease would be more likely to affect "all trees." In Experiment 3, the conclusion category was eliminated altogether, and participants were asked to generate a list of other affected trees. Among these populations, typicality and diversity effects were weak to nonexistent. Instead, experts' reasoning was influenced by "local" coverage (extension of the property to members of the same folk family) and causal-ecological factors. The authors concluded that domain knowledge leads to the use of a variety of reasoning strategies not captured by current models of category-based induction.

Evaluation of exemplar-based generalization and the abstraction of categorical information.

This article reformulates and reanalyzes a problem originally put forth by Homa, Sterling, and Trepel (1981). The question is whether a pure, exemplar-based abstraction process is an adequate model of category learning or whether it is necessary to postulate an additional prototype-abstraction process. Based on quantitative discrepancies from a pure, exemplar-based model, Homa et al. argued that it was necessary to recognize the operation of a prototype-abstraction process in order to fully explain their results. However, Homa et al. never actually fit the exemplar plus prototype model to the data to determine if indeed the additional prototype process could explain the deviations from the pure exemplar model. The present article compared the pure exemplar model with a mixed (exemplar plus prototype) model and did not find consistent evidence requiring the postulation of an additional prototype-abstraction process. These results point out the difficulty of distinguishing alternative classification models and underscore the need for careful analytic work in this area.

Given versus induced category representations: use of prototype and exemplar information in classification.

Acquisition of category-level information can be based on experience with category members (induced) as well as on direct presentation of prototypical values (given). To investigate the effects of these two types of information, a relational coding model of categorization was developed in which classification is based on a mixture of exemplar and prototype information. In two experiments, subjects learned about two ill-defined categories. Stimuli were geometric shapes varying along four binary-valued dimensions. For three groups of subjects, training consisted of (a) experience with exemplars only, (b) learning prototype values followed by exemplar experience, or (c) learning prototype values concurrently with exemplar experience. Following training, all subjects received classification tests on prototype values as well as on old and new exemplars. By varying the relative use of prototype and exemplar information, the mixture model accurately accounted for category judgements in all three groups. For subjects directly presented with prototype values, classification was based on a mixture of similarity to prototypes and to stored exemplars. In contrast, subjects who only received experience with exemplars appeared to base their category judgements solely on similarity to stored exemplars, even though they could accurately judge the prototype values. The two components of the mixture model are related to subjects' classification strategies and the nature of abstracted, category-level information.

Correlated symptoms and simulated medical classification.

Category learning theories can be separated into those that expect judgments to be sensitive to configural information and those that expect judgments to be based on a weighted, additive summation of information. Predictions of these two classes of models were investigated in a simulated medical diagnosis task. Subjects learned about a fictitious disease or about two diseases from hypothetical case studies in which some symptoms were correlated with each other and others were independent. Following this initial training, subjects were presented either with pairs of new cases and asked to judge which was more likely to have the disease or with a single case and asked which disease was present. Across four experiments, subjects proved to be sensitive to configural information. When choosing between pairs of new cases, subjects tended to choose the case that preserved the correlation over the case that broke the correlation, even when the case with correlated symptoms contained fewer typical symptoms. When judging which disease was present in a single case, subjects' diagnoses were determined primarily by the correlated symptoms. Implications of these findings to process models of categorization are discussed.

Validation of continuous thermodilution cardiac output in critically ill patients with analysis of systematic errors.

PURPOSE: Bolus thermodilution cardiac output (BCO) measurements are affected by variations in injectate volume, rate, and temperature. These variations are eliminated when CO is measured by a continuous automated thermal technique (CCO). Further, CCO eliminates the need for fluid boluses, reduces contamination risk, requires no operator, and provides a continuous CO trend. We prospectively evaluated CCO versus BCO in a population of critically ill adults with low, normal, and high CO states. We sought to discern any systematic effects of temperature fluctuations or signal-to-noise-ratios (SNR) on disparities between BCO and CCO measurements and also sought to assess the relative cost effectiveness of the CCO system. MATERIALS AND METHODS: Pulmonary artery catheterizations were performed in a convenience sample of 20 patients over 6 months. BCO data were obtained using a standardized protocol. Three bolus injections of 5% dextrose were given when each CO was within 10% of the median before averaging; otherwise five boluses were given, with the high and low values eliminated before averaging. Injectates were administered randomly through the respiratory cycle and at 1-minute intervals. CCO measurements were recorded from a Vigilance monitor pre and post BCO measurements, yielding an average CCO value. Also recorded were pre- and post-core temperatures and SNR during the first CCO measurement. Cost data included estimates of operator time for BCO determinations as well as costs of Intellicath (Baxter-Edwards, Irvine, CA) pulmonary artery catheters, Vigilance (Baxter-Edwards, Irvine, CA) monitors, conventional catheters, and injectates. RESULTS: Of the 20 patients, 15 were mechanically ventilated. A total of 306 paired CO values were obtained for analysis. CCO ranged from 2.5 to 14.4 L/min and BCO from 2.4 to 13.3 L/min. Absolute differences between CCO and BCO measurements increased with increasing CO, but percentage differences did not. Of the paired values, 77% were within 1 L/min of one another. Temperature instability and SNR independently had weak correlations with CCO/BCO disparities. The Vigilance system had a slightly higher net cost than conventional BCO, although no economical value was assigned to the clinical usefulness of continuous, as opposed to intermittent, CO monitoring. CONCLUSIONS: Continuous CO is a reliable and cost-effective alternative to bolus thermodilution CO for critically ill patients in low, normal, and high CO states.

Presentation order and recognition of categorically related examples.

Two experiments are described in which different groups of participants saw the same examples in different orders and then were given an old-new recognition test. The learning and test examples were created from different combinations from four binary-valued dimensions. One order (small change) was constructed to maximize the similarity between successive examples, and the other order (large change) minimized the similarity across successive examples. The small change condition was consistently associated with better old-new recognition than the large change condition was. These results are discussed in terms of exemplar-guided encoding and models of category generalization.

Asymmetries of comparison.

Tversky's (1977) seminal work on directionality injudgments of similarity demonstrated that people may not judge the similarity of A to B to be equal to the similarity of B to A. In a series of studies, we investigated comparison asymmetries. In Experiment 1, our aim was to extend Tversky's findings to a heterogeneous stimulus set, but no reliable asymmetries were observed. Experiment 2 employed a variety of comparison judgments, and, although some of these measures showed asymmetries, we still failed to observe asymmetries in rated similarity. A final attempt to obtain asymmetries used direction as a within-subjects factor, and for the first time, rating asymmetries were observed. Our data reinforce the idea of comparison asymmetries but suggest that similarity rating asymmetries are only observed under quite circumscribed conditions.

Broadening behavioral decision research: multiple levels of cognitive processing.

The area of behavioral decision research--specifically, the work on heuristics and biases--has had a tremendous influence on basic research, applied research, and application over the last 25 years. Its unique juxtaposition against economics has provided important benefits, but at the cost of leaving it disconnected from too much of psychology. This paper explores an expanded definition of behavioral decision research through the consideration of multiple levels of cognitive processing. Rather than being limited to how decision makers depart from optimality, we offer a broader analysis of how decision makers define the decision problem and link decisions to goals, as well as a more detailed focus on processes associated with implementing decisions.

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 semantic side of decision making.

The research reported in this paper follows the perspective that decision making is a meaningful act that conveys information. Furthermore, the potential meanings associated with decision options may affect the decisions themselves. This idea is examined in the contexts of compensation, donation, and exchange. In general, judgments were relation dependent and meaning dependent. Furthermore, the results show nonmonotonicities and limited substitutability in a pattern that challenges straightforward ways of mapping decisions onto a common currency of utility.

Developmental study of similarity judgments involving dimensions.

In order to examine the nature of dimensional processing in children, kindergarten and third grade children were asked to make similarity judgments for unidimensional sets of stimuli differing in color (hue), size, and shape, respectively. Age differences were generally confined to the color set. The judgments of the older children in their age group than were the younger children's. The frequency of good-fitting scaling solutions was also higher for the older children. The processing of color in a relational manner thus seems to develop more slowly than relational processing of size or shape. Results from any task which depends on or is facilitated by relational processing could be altered by the dimensions used. The methods developed in the paper also provide an alternate method of studying seriation .