Estimating the rapid haemodynamic effects of passive leg raising in critically ill patients using bioreactance.

BACKGROUND: Rapid detection of changes in cardiac index (CI) in real time using minimally invasive monitors may be of clinical benefit. We tested whether the Starling-SV bioreactance device, which averages CI over a short 8 s period, could assess the effects of passive leg raising (PLR), a clinical test that is recommended to assess fluid responsiveness during septic shock. METHODS: In 32 critically ill patients, we measured CI by transpulmonary thermodilution (PiCCO2, CItd), pulse contour analysis (PiCCO2, CIPulse), and the Starling-SV device (CIStarling) at baseline. CIPulse and CIStarling were measured again at the end of a PLR test. In the 13 patients with a positive PLR test, CItd, CIPulse, and CIStarling were measured before and after a 500 ml saline infusion. The primary outcome was relative changes from baseline measurements in CItd, CIPulse, and CIStarling. Secondary outcomes compared absolute values measured by each method. RESULTS: Relative changes in CIPulse and CItd were significantly correlated (r=0.82; n=45; P<0.001), with an 89% concordance rate (n=45 paired measurements). Relative changes in CIStarling and CItd were also significantly correlated (r=0.59; n=45; P<0.001) with a 78% concordance rate. For absolute measures of CI (n=77 paired measurements), the bias between CIPulse and CItd was 0.01 L min-1 m-2 (limits of agreement, -0.49 and 0.51 L min-1 m-2; 15% percentage error). Bias between CIStarling and CItd was 0.03 L min-1 m-2 (limits of agreement, -1.61 and 1.67 L min-1 m-2; 48% percentage error). CONCLUSIONS: In critically ill patients, a non-invasive bioreactance device with a shorter averaging period assessed a passive leg raising test with reasonable accuracy.

Inept reasoners or pragmatic virtuosos? Relevance and the deontic selection task.

Most individuals fail the selection task, selecting P and Q cases, when they have to test descriptive rules of the form "If P, then Q". But they solve it, selecting P and not-Q cases, when they have to test deontic rules of the form "If P, then must Q". According to relevance theory, linguistic comprehension processes determine intuitions of relevance that, in turn, determine case selections in both descriptive and deontic problems. We tested the relevance theory predictions in a within-participants experiment. The results showed that the same rule, regardless of whether it is tested descriptively or deontically, can be made to yield more P and Q selections or more P and not-Q selections. We conclude that the selection task does not provide a tool to test general claims about human reasoning.

Hypothesis testing in a rule discovery problem: when a focused procedure is effective.

We investigated individuals' ability to use negative evidence in hypothesis testing. We compared performance in two versions of Wason's (1960) rule discovery problem. In the original version, a triple of numbers--(2, 4, 6)--was presented as an example of a rule that the experimenter had in mind (i.e., "increasing numbers"). Participants had to discover the rule by proposing new triples. In the other version, the same triple was presented as a counter-example to the experimenter's rule (i.e., "decreasing numbers"). We predicted that, in both conditions, participants would form hypotheses based on the features of the triple, and test only instances of the hypothesized rule. However, in the counter-example condition, such focused testing would invariably produce negative evidence. As a consequence, participants would be forced to revise their hypotheses. The reported results corroborated our predictions: Participants solved the counter-example version significantly better than the original problem.

Solving probabilistic and statistical problems: a matter of information structure and question form.

Is the human mind inherently unable to reason probabilistically, or is it able to do so only when problems tap into a module for reasoning about natural frequencies? We suggest an alternative possibility: naive individuals are able to reason probabilistically when they can rely on a representation of subsets of chances or frequencies. We predicted that naive individuals solve conditional probability problems if they can infer conditional probabilities from the subset relations in their representation of the problems, and if the question put to them makes it easy to consider the appropriate subsets. The results of seven studies corroborated these predictions: when the form of the question and the structure of the problem were framed so as to activate intuitive principles based on subset relations, naive individuals solved problems, whether they were stated in terms of probabilities or frequencies. Otherwise, they failed with both sorts of information. The results contravene the frequentist hypothesis and the evolutionary account of probabilistic reasoning.

Illusions in reasoning about consistency.

Reasoners succumb to predictable illusions in evaluating whether sets of assertions are consistent. We report two studies of this computationally intractable task of "satisfiability." The results show that as the number of possibilities compatible with the assertions increases, the difficulty of the task increases, and that reasoners represent what is true according to assertions, not what is false. This procedure avoids overloading memory, but it yields illusions of consistency and of inconsistency. These illusions modify our picture of human rationality.

Naive probability: a mental model theory of extensional reasoning.

This article outlines a theory of naive probability. According to the theory, individuals who are unfamiliar with the probability calculus can infer the probabilities of events in an extensional way: They construct mental models of what is true in the various possibilities. Each model represents an equiprobable alternative unless individuals have beliefs to the contrary, in which case some models will have higher probabilities than others. The probability of an event depends on the proportion of models in which it occurs. The theory predicts several phenomena of reasoning about absolute probabilities, including typical biases. It correctly predicts certain cognitive illusions in inferences about relative probabilities. It accommodates reasoning based on numerical premises, and it explains how naive reasoners can infer posterior probabilities without relying on Bayes's theorem. Finally, it dispels some common misconceptions of probabilistic reasoning.

The effect of premise order in conditional reasoning: a test of the mental model theory.

The difference in difficulty between modus ponens (if p then q; p; therefore q) and modus tollens (if p then q; not-q; therefore not-p) arguments has been traditionally explained by assuming that the mind contains a rule for modus ponens, but not for modus tollens. According to the mental model theory, modus tollens is a more difficult deduction than modus ponens because people do not represent the case not-q in their initial model of the conditional. On the basis of this theory, we predicted that conditions in which reasoners are forced to represent the not-q case should improve correct performance on modus tollens. In particular, we predicted that the presentation of the minor premise (not-q) as the initial premise should produce facilitation. Experiment 1 showed that this is the case: whereas the inversion of the premise order did not affect modus ponens, it produced a significant increase of valid conclusions for modus tollens. Experiment 2 showed that this facilitation does not depend on the negative form (contrary vs. contradictory) of the minor premise. Experiments 3 and 4 (and/or some of their replications) demonstrated that facilitation also occurs when participants are asked to find the cases compatible with not-q or to evaluate a p conclusion. No premise order effect was found for sentences which make explicit the not-q case right from the start, i.e. p only if q conditionals and biconditionals (Experiments 5 and 6). Finally, Experiments 7 and 8 showed that the conditional fallacies are not significantly affected by the premise order.

Relevance theory explains the selection task.

We propose a general and predictive explanation of the Wason Selection Task (where subjects are asked to select evidence for testing a conditional "rule"). Our explanation is based on a reanalysis of the task, and on Relevance Theory. We argue that subjects' selections in all true versions of the Selection Task result from the following procedure. Subjects infer from the rule directly testable consequences. They infer them in their order of accessibility, and stop when the resulting interpretation of the rule meets their expectations of relevance. Subjects then select the cards that may test the consequences they have inferred from the rule. Order of accessibility of consequences and expectations of relevance vary with rule and context, and so, therefore, does subjects' performance. By devising appropriate rule-context pairs, we predict that correct performance can be elicited in any conceptual domain. We corroborate this prediction with four experiments. We argue that past results properly reanalyzed confirm our account. We discuss the relevance of the Selection Task to the study of reasoning.

Focussing in reasoning and decision making.

Our principal hypothesis is that reasoning and decision making are alike in that they both depend on the construction of mental models, and so they should both give rise to similar phenomena. In this paper, we consider one such phenomenon, which we refer to as "focussing": individuals are likely to restrict their thoughts to what is explicitly represented in their models. We show that focussing occurs in four domains. First, individuals fail to draw inferences in the modus tollens form: if p then q, not-q, therefore not-p, because they focus on their initial models of the conditional, which make explicit only the case where the antecedent (p) and consequent (q) occur. Second, in Wason's selection task, they similarly tend to select only those cards that are explicitly represented in their initial models of the conditional rule. Third, their requests for information in order to enable them to make a decision about whether or not to carry out a certain action are focussed on the action to the exclusion of alternatives to it. In each of these cases, we show how the focussing bias can be reduced by certain experimental manipulations. Finally, in counterfactual reasoning, focussing underlies individuals' attempts to imagine an alternative scenario that avoids an unfortunate ending to a story.

Children's communicative abilities revisited: verbal versus perceptual disambiguating strategies in referential communication.

The way seven- and nine-year-old French children and adults interpret ambiguous object descriptions was studied in four experiments. All four experiments followed the same basic procedure and consisted of two phases. During the training phase, plastic blocks varying in shape, colour and size were associated with fruit names. Some objects were always given just one label, the generic term, whereas others could be given either the generic or the specific label. For example, large circles were referred to as 'pommes' ('apples'), and large blue circles as 'reinettes' (a kind of apple). Still others were given no name at all. During the test phase of the experiment, subjects were presented with referentially ambiguous messages and asked to point to a given object (Experiments 1, 2 and 3) or to draw an object (Experiment 4). The messages consisted of either a generic term preceded by an article (e.g. '(la pomme'-'the apple') or a verbal description based on a colour adjective (e.g. 'le bleu'-'the blue one'). When presented with the generic term, older children and adults persistently chose the object for which no specific term had been given during the training phase. When presented with an adjective description, they chose the referent for which no fruit name had been given during the training phase. Younger children's choices depended on whether the article preceding the description was definite or indefinite. These results are consistent with the Gricean approach to referential communication proposed by Jackson & Jacobs (1982) and with an extended version of the principle of contrast proposed by Clark (1987, 1988).

Mental representation and hypothetico-deductive reasoning: the case of the THOG problem.

This article reports three experiments that deal with the source of the difficulty of Wason's (1977) THOG problem. The solution of this problem demands both the postulation of hypotheses and a combinatorial analysis of their consequences. Experiment 1 showed that the generation of the hypotheses is not in itself sufficient to solve the problem. Experiment 2 showed that a version presenting a plausible context for separating the level of data from that of hypotheses produced a better performance than both the original abstract version and a thematic version lacking the plausible context separating the levels. Experiment 3 gave evidence that this context can produce facilitation even with the geometric material of the classic version. This experiment also showed that a pictorial presentation of data and a verbal presentation of hypotheses affect performance negatively. The results demonstrate the role of problem representation in problem solving, and, in particular, the role of homogeneity in representing data and hypotheses in hypothetico-deductive reasoning.

[A case report of prolonged hemolytic anemia in an infant due to a partial exchange transfusion]. / Prikaz slucaja protrahirane hemolizne anemije dojenceta zbog djelomicne ekssangvinotransfuzije.

An infant at the age of one month was admitted to hospital due to anaemia and icterus. Premature delivery was induced because of Rh immunisation. Newborn's grave condition permitted only one "blood volume" exchange transfusion and as a consequence prolonged haemolytic anaemia occurred. At the age of one month anti Rh-D antibody persisted in the infant circulation with the titre 1:16 in an indirect antiglobulin method.