Biomedical subjects

Simon J Handley

Publications and source records attributed to Simon J Handley.

5 recordsLinked to original sources

PubMed2003

Conditionals and conditional probability.

The authors report 3 experiments in which participants were invited to judge the probability of statements of the form if p then q given frequency information about the cases pq, p not q, not pq, and not p not q (where not = not). Three hypotheses were compared: (a) that people equate the probability with that of the material conditional, 1 - P(p not q); (b) that people assign the conditional probability, P(q/p); and (c) that people assign the conjunctive probability P(pq). The experimental evidence allowed rejection of the 1st hypothesis but provided some support for the 2nd and 3rd hypotheses. Individual difference analyses showed that half of the participants used conditional probability and that most of the remaining participants used conjunctive probability as the basis of their judgments.

Color Perception↗

PubMed2002

Alternative antecedents, probabilities, and the suppression of fallacies in Wason's selection task.

Three experiments examined the influence of a second rule on the pattern of card selections on Wason's selection task. In Experiment 1 participants received a version of the task with a single test rule or one of two versions of the task with the same original test rule together with a second rule. The probability of q was manipulated in the two-rules conditions by varying the size of the antecedent set in the second rule. The results showed a significant suppression of q card and not-p card selections in the alternative-rule conditions, but no difference as a function of antecedent set size. In Experiment 2 the size of the antecendent set in the two-rules conditions was manipulated using the context of a computer printing double-sided cards. The results showed a significant reduction of q card selections in the two-rules conditions, but no effect of p set size. In Experiment 3 the scenario accompanying the rule was manipulated, and it specified a single alternative antecedent or a number of alternative antecedents. The q card selection rates were not affected by the scenario manipulation but again were suppressed by the presence of a second rule. Our results suggest that people make inferences about the unseen side of the cards when engaging with the task and that these inferences are systematically influenced by the presence of a second rule, but are not influenced by the probabilistic characteristics of this rule. These findings are discussed in the context of decision theoretic views of selection task performance (Oaksford & Chater, 1994).

Choice Behavior↗

PubMed2002

Conditional reasoning and the Tower of Hanoi: the role of spatial and verbal working memory.

This paper reports a study that investigated the relationships between verbal and spatial measures of working memory capacity and performance on the Tower of Hanoi and a conditional reasoning task. Four working memory measures were included, a simple word span, a simple spatial span, a complex verbal span and a complex spatial span. The participants were 70 undergraduate students. Solution time on the Tower of Hanoi task correlated highly with both measures of spatial memory capacity, but not with the verbal working memory spans. In contrast, logical performance on the conditional reasoning task correlated highly with the complex verbal working memory span, but not with the spatial spans. A confirmatory factor analysis of the data elicited a best-fit model comprising a correlated spatial and verbal factor. The results are interpreted in the context of recent work that suggests a dissociation between spatial and verbal resources at the level of the central executive.

Cognition↗

PubMed2002

Generating alternatives: a key component in human reasoning?

According to mental models theory, a key aspect of deductive reasoning is the production of alternative models that can falsify provisional conclusions. In the present paper, the possibility is investigated that there are individual differences in the ability to produce alternative models. The results indicate that some people do not proceed beyond the first model when they reason with syllogisms but that others do. Furthermore, the ability to generate alternatives can be independently measured by asking participants to generate different representations of pairs of premises. These findings support the predictions of mental models theory and also indicate the potential importance of alternatives generation as a measure of individual differences in processing style.

Adolescent↗

PubMed2002

Background beliefs in Bayesian inference.

We report five experiments in which the role of background beliefs in social judgments of posterior probability was investigated. From a Bayesian perspective, people should combine prior probabilities (or base rates) and diagnostic evidence with equal weighting, although previous research shows that base rates are often underweighted. These experiments were designed so that either piece of information was supplied either by personal beliefs or by presented statistics, and regression analyses were performed on individual participants to assess the relative influence of information. We found that both prior probabilities and diagnostic information significantly influenced judgments, whether supplied by beliefs or by statistical information, but that belief-based information tended to dominate the judgments made.

Bayes Theorem↗