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[Fatigue and practice effects during cognitive tasks lasting several hours].

In psychometric studies of cognitive performance that last several hours there are two major potential influences on performance. Fatigue and loss of motivation may lead to a drop in performance while effects of practice on similar tasks can possibly help to improve results. Besides the effects on mean scores there is also the possibility of a change in the reliability or in the relations between single tasks and the constructs intended to be measured, thus an effect on validity. In two studies with subjects working on intelligence and working memory tasks for a total of 9 hours distributed over 2 days in each study we tried to capture and separate effects of practice and fatigue using a quasi-experimental manipulation. In both studies (N = 128 and N = 133) the participants worked on the Berlin Structure of Intelligence Test (BIS-test) and on batteries of computerized working memory tasks. Groups of subjects were assigned to experimental conditions in which they worked on two parallel versions of a working memory task at the beginning and the end of one session in the order A/B (condition one), B/A (condition two) or on both versions at the end (condition three). In one of the studies subjects also completed a fatigue questionnaire at the beginning and the end of the session and two personality scales. Results show that there are weak effects of practice but only a trivial loss of performance due to the cognitive strain of several hours. Changes of reliabilities and of correlations with criteria are not significant.