the heuristics-and-biases approach to statistical reasoning is and is not about. At issue is the imposition of unnecessarily narrow norms of sound reasoning that are used to diagnose so-called cognitive illusions and the continuing reliance on vague heuristics that explain everything and nothing. D. Kahneman and A. Tversky (1996) incorrectly asserted that Gigerenzer simply claimed that frequency formats make all cognitive illusions disappear. In contrast, Gigerenzer has proposed and tested models that actually predict when frequency judgments are valid and when they are not. The issue is not whether or not. or how often, cognitive illusions disappear. The focus should be rather the construction of detailed models of cognitive processes that explain when and why they disappear. A postscript responds to Kahneman and Tversky's (1996) postscript. I welcome Kahneman and Tversky's (1996) reply to my critique (e.g., Gigerenzer, 1991, 1994; Gigerenzer & Murray, 1987) and hope this exchange will encourage a rethinking of research strategies. I emphasize research strategies, rather than specific empirical results or even explanations of those results, because I believe that this debate is fundamentally about what

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Early studies of intuitive judgment and decision making conducted with the late Amos Tversky are reviewed in the context of two related concepts: an analysis of accessibility, the ease with which thoughts come to mind; a distinction between effortless intuition and deliberate reasoning. Intuitive thoughts, like percepts, are highly accessible. Determinants and consequences of accessibility help explain the central results of prospect theory, framing effects, the heuristic process of attribute substitution, and the characteristic biases that result from the substitution of nonextensional for extensional attributes. Variations in the accessibility of rules explain the occasional corrections of intuitive judgments. The study of biases is compatible with a view of intuitive thinking and decision making as generally skilled and successful.

An account of grammatical acquisition is developed within the parametersetting framework applied to a generalized categorial grammar (GCG). The GCG is embedded in a default inheritance network yielding a natural partial ordering (reflecting generality) of parameters which determines a partial order for parameter setting. Computational simulation shows that several resulting acquisition procedures are effective on a parameter set expressing major typological distinctions based on constituent order, and defining 70 distinct full languages and over 200 subset languages. The effects on acquisition of inductive bias, that is, of differing initial parameter settings, are explored via computational simulation. Computational simulation of populations of language learners and users instantiating the acquisition model show: 1) that variant acquisition procedures, with differing inductive biases, exert differing selective pressures on the evolution of language(s); 2) acquisition proc...

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Findings in recent research on the `conjunction fallacy ' have been taken as evidence that our minds are not designed to work by the rules of probability. This conclusion springs from the idea that norms should be content-blind Ð in the present case, the assumption that sound reasoning requires following the conjunction rule of probability theory. But content-blind norms overlook some of the intelligent ways in which humans deal with uncertainty, for instance, when drawing semantic and pragmatic inferences. In a series of studies, we ®rst show that people infer nonmathematical meanings of the polysemous term `probability' in the classic Linda conjunction problem. We then demonstrate that one can design contexts in which people infer mathematical meanings of the term and are therefore more likely to conform to the conjunction rule. Finally, we report evidence that the term `frequency ' narrows the spectrum of possible interpretations of `probability ' down to its mathematical meanings, and that this fact Ð rather than the presence or absence of `extensional cues ' Ð accounts for the low proportion of violations of the conjunction rule when people are asked for

Evolutionary approaches to judgment under uncertainty have led to new data showing that untutored subject reliably produce judgments that conform to may principles of probability theory when (a) they are asked to compute a frequency instead of the probability of a single event, and (b) the relevant information is expressed as frequencies. But are the frequencycomputation systems implicated in these experiments better at operating over some kinds of input than others? Principles of object perception and principles of adaptive design led us to propose the individuation hypothesis: that these systems are designed to produce wellcalibrated statistical inferences when they operate over representations of “whole ” objects, events, and locations. In a series of experiments on Bayesian reasoning, we show that human performance can be systematically improved or degraded by varying whether a correct solution requires one to compute hit and false-alarm rates over “natural ” units, such as whole objects, as opposed to inseparable aspects, views, and other parsings that violate evolved principles of object construal. The ability to make well-calibrated probability judgments depends, at a very basic level, on the ability to count. The

Purpose. To test whether physicians ’ diagnostic inferences can be improved by communicating information using natural frequencies instead of probabilities. Whereas probabilities and relative frequencies are normalized with respect to disease base rates, natural frequencies are not normalized. Method. The authors asked 48 physicians in Munich and Düsseldorf to determine the positive predictive values (PPVs) of four diagnostic tests. Information presented in the four problems appeared either as probabilities (the traditional way) or as natural frequencies. Results. When the information was presented as probabilities, the physicians correctly estimated the PPVs in only 10 % of cases. When the same information was presented as natural frequencies, that percentage increased to 46%. Conclusion. Representing information in natural frequencies is a fast and effective way of facilitating diagnostic insight, which in turn helps physicians to better communicate risks to patients, and patients to better understand these risks. What does a positive medical test result mean? Physicians often have diffi culty inferring the probability of a disease from statistical information relevant to positive test results. 1–5 In one study,

Human cognition is often biased, from judgments of the time of impact of approaching objects all the way through to estimations of social outcomes in the future. We propose these effects and a host of others may all be understood from an evolutionary psychological perspective. In this article, we elaborate error management theory (EMT; Haselton & Buss, 2000). EMT predicts that if judgments are made under uncertainty, and the costs of false positive and false negative errors have been asymmetric over evolutionary history, selection should have favored a bias toward making the least costly error. This perspective integrates a diverse array of effects under a single explanatory umbrella, and it yields new content-specific predictions. Better safe than sorry. (folk wisdom) Nothing ventured, nothing gained. (contradictory folk wisdom) These two wisdoms seem contradictory. The first urges caution, whereas the second reminds us that we have nothing to lose and should throw caution to the

Human language acquisition, and in particular the acquisition of grammar, is a partially-canalized, strongly-biased but robust and e cient procedure. For example, children prefer to induce lexically compositional rules (e.g. Wanner and Gleitman, 1982) despite the use, in every attested human language, of constructions, such as morphological negation or non-compositional idioms. And, most parameters of grammatical variation set during language acquisition appear to have default or so-called unmarked values retained in the absence of robust counter-evidence (e.g. Bickerton, 1984 � Hyams, 1986 � Lightfoot, 1992). A variety of explanations have been o ered for the emergence of a partially-innate language acquisition device (LAD) with such properties based on saltation (Berwick, 1998 � Bickerton, 1990, 1998) or genetic assimilation (Pinker and Bloom, 1990). But none provide a coherent detailed account of both the emergence and maintenance of a LAD in an evolving population. The account proposed here is that a minimal LAD emerged via recruitment of general-purpose (Bayesian) learning mechanisms (e.g. Staddon, 1988 � Cosmides and Tooby, 1996) to a speci cally-linguistic mental representation capable of expressing mappings from the `language of thought ' to realizable, essentially linearized, encodings of propositions of the language of thought. However, the selective pressure favouring such adevelopment, and its subsequent maintenance and re nement, is only coherent given a coevolutionary scenario in which a (proto)language supporting successful communication within a population had already itself evolved on a historical timescale (e.g. Hurford, 1987 � Kirby, 1998 � Steels, 1998) and continued to coevolve with the LAD (e.g. Briscoe, 1997, 1998a,b). The model of the LAD presented here builds on and extends previous work in the parameter setting