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In this study we aim to examine how the implicit learning of statistical regularities of successive stimuli affects the ability to exert cognitive control. In three experiments, sequences of flanker stimuli were segregated into pairs, with the second stimulus contingent on the first. Response times were reliably faster for the second stimulus if its congruence tended to match the congruence of the preceding stimulus, even though most participants were not explicitly aware of the statistical regularities (Experiment 1). In contrast, performance was not enhanced if the congruence of the second stimuli tended to mismatch the congruence of the first stimulus (Experiment 2). The lack of improvement appears to result from a failure of learning mismatch contingencies (Experiment 3). The results suggest that implicit learning of inter-stimulus relationships can facilitate cognitive control. [ABSTRACT FROM AUTHOR]

Most real-world judgments and decisions require the consideration of multiple types of evidence. For example, judging the severity of environmental damage, medical illness, or negative economic trends often involves tracking and integrating evidence from multiple sources (i.e. different natural disasters, physical symptoms, or financial indicators). We hypothesized that the requirement to track and integrate across distinct types of evidence would affect severity judgments of multifaceted problems, compared to simpler problems. To test this, we used scenarios depicting crop damage. Each scenario involved either two event types (i.e. mold damage and insect damage), or one event type. Participants judged the quality of the crop following each scenario. In Experiments 1 and 2, subjective judgments were attenuated if the scenario depicted multiple event types, relative to scenarios depicting single event types. This was evident as a shallower slope of subjective severity ratings, as a function of objectively quantifiable severity, for scenarios with multiple event types. In Experiment 3, we asked whether alternation between event types might contribute to this attenuation. Each scenario contained two event types, and the sequence of events either alternated frequently between types or was organized into two sequential groups. Subjective judgments were attenuated for scenarios with frequently alternating sequences. The results demonstrate that alternation between distinct event types attenuates subjective judgments of severity. This suggests that a requirement to integrate evidence across multiple sources places extra demands on the cognitive system, which reduces the perceived evidence strength. [ABSTRACT FROM AUTHOR]