Judgments of a treatment’s effectiveness are usually biased by the probability with which the outcome (e.g., symptom relief) appears: even when the treatment is completely ineffective (i.e., there is a null contingency between cause and outcome), judgments tend to be higher when outcomes appear with high probability. In this research, we present ambiguous stimuli, expecting to find individual differences in the tendency to interpret them as outcomes. In Experiment 1, judgments of effectiveness of a completely ineffective treatment increased with the spontaneous tendency of participants to interpret ambiguous stimuli as outcome occurrences (i.e., healings). In Experiment 2, this interpretation bias was affected by the overall treatment-outcome contingency, suggesting that the tendency to interpret ambiguous stimuli as outcomes is learned and context-dependent. In conclusion, we show that, to understand how judgments of effectiveness are affected by outcome probability, we need to also take into account the variable tendency of people to interpret ambiguous information as outcome occurrences.

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Two experiments address the habituation of photonegative and exploratory responses in the flatworm planaria (Dugesia). Planarians possess a well-documented photonegative response; Experiment 1 showed that repeated exposures to a bright light source with short inter trial intervals (ITIs) within 1 experimental session gradually weakens the unconditioned photonegative response. In addition, it was found that presentation of an unexpected arousal-increasing stimulus (dropped water or a shock) temporarily re-establishes the photonegative response. Experiment 2 addressed the development of long-term habituation; we recorded the locomotor activity of the animals exposed to an inescapable bright light. Experiments 2A and 2B showed that planarians develop long-term habituation but only when they were trained in relatively novel contexts; when they were trained in familiar contexts (in surfaces similar to the ones in the home) the development of habituation was severely impaired. The results are discussed by reference to the theory of short- and long-term habituation put forward by Allan R. Wagner (Wagner, 1976), highlighting the impact that this theory has had in the research of invertebrate learning.

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Previous research proposed that cognitive biases contribute to produce and maintain the symptoms exhibited by deluded patients. Specifically, the tendency to jump to conclusions (i.e., to stop collecting evidence soon before making a decision) has been claimed to contribute to delusion formation. Additionally, deluded patients show an abnormal understanding of cause-effect relationships, often leading to causal illusions (i.e., the belief that two events are causally connected, when they are not). Both types of bias appear in psychotic disorders, but also in healthy individuals. In two studies, we test the hypothesis that the two biases (jumping to conclusions and causal illusions) appear in the general population and correlate with each other. The rationale is based on current theories of associative learning that explain causal illusions as the result of a learning bias that tends to wear off as additional information is incorporated. We propose that participants with higher tendency to jump to conclusions will stop collecting information sooner in a causal learning study than those participants with lower tendency to jump to conclusions, which means that the former will not reach the learning asymptote, leading to biased judgments. The studies provide evidence in favour that the two biases are correlated but suggest that the proposed mechanism is not responsible for this association.