Fatigue and practice effects during cognitive tasks lasting several hours

In psychometric studies of cognitive performance that last several hours th ere an two major potential influences on performance. Fatigue and loss of m otivation may lead to a drop in performance while effects of practice on si milar tasks can possibly help to improve results. Besides the effects on me an scores then is also the possibility of a change in the reliability or in the relations between single tasks and the constructs intended to be measu red, thus an effect on validity. In two studies with subjects working on intelligence and working memory tas ks 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-experim ental manipulation. In both studies (N = 128 and N = 133) the participants worked on the Berlin Structure of Intelligence Test (BIS-test) and on batte ries of computerized working memory tasks. Groups of subjects were assigned to experimental conditions in which they worked on two parallel versions o f 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 e nd (condition three). In one of the studies subjects also completed a fatigue questionnnaire at t he beginning and the end of the session and two personality scales. Results show that there are weak affects of practice but only a trivial los s of performance due to the cognitive strain of several hours. Changes of r eliabilities and of correlations with criteria are not significant.