Psychopharmacology (2012) 220:293–301 room, in which the luminosity was kept constant during the study. The test battery consisted of validated and reliable standardized tests measuring different aspects of memory functioning (Sternberg memory scanning test), psychomo- tor performance (tracking test), attention (divided attention test), and information processing (DSST). Quality of performance was assessed by recording the percentage of errors on the tests. Before the start of the actual studies, participants were trained on the tests to attain baseline performance and to become familiar with test procedures. Sternberg memory scanning test This test is designed to measure various aspects of working memory. Working memory is especially important at the strategic/navigational level of driving behavior (e.g., re- membering which side-way should be taken). After learning a memory set of one to five digits (ranging from 0 to 9), a single digit (or probe) was presented on the computer screen. Subjects were instructed to indicate by button press whether the probe was part of the memory set (presented, right hand button) or not (not presented, left hand button). A total of 100 different memory sets were presented. Mean reaction time (RT, millisecond) and percent errors are the parameters of interest. Time on task is ±12 min. Continuous tracking test This test is designed to measure psychomotor coordination. Tracking skills are especially important at the operational/ control level of driving behavior (e.g., keeping the car in a steady position within the lane). Subjects were instructed to keep an unstable bar in the middle of a horizontal plane by counteracting or reverse its movements with the aid of a computer mouse. If the unstable bar hit the edges of the plane, they had to start again. An easy version (λ = 150) and a hard version (λ = 300) of the tracking test were conducted (lambda is a measure of instability of the moving bar: the higher lambda, the more difficult the task). The parameter for tracking accuracy is the root mean square (R.M.S.) of the deviation of the unstable bar. Time on task is ±8 min. Divided attention test Divided attention is especially important at the maneuvering/ tactical level of driving behavior (e.g., passing another car while changing gear). Simultaneously, the easy tracking test (right hand) and a memory scanning test (fixed memory set size of four digits, left hand) were performed. Subsequently, digits (ranging from 0 to 9) were presented on the computer screen, and participants had to indicate by button press whether the 297 digit was part of the memory set or not. Parameters are the R.M.S., the mean reaction time (milliseconds) and percent errors. Time on task is ±8.5 min. Digit symbol substitution test This test is designed to measure information processing, an ability that is important at all levels of driving behavior. The digit symbol substitution test (DSST) is a paper-and- pencil test in which subjects have to match accompanying symbols and digits. Subjects were instructed to complete as many pairs as possible within 90 s. Different versions of the tests were used every test day. The number of correct completed pairs was the variable of interest. Statistical analysis For each treatment, difference scores from placebo were calculated. This was done for each dependent variable. The data of the three studies were combined into a single dataset to allow comparisons between changes in the primary parameter of the driving test (SDLP) and difference scores of the psychometric test variables. Pearson r correlations were computed (significance was established if p < 0.05, two-tailed). The analyses were done for all data together, as well as for the individual drug treatments. Finally, a step- forward regression analysis was conducted to determine if a combination of test variables adequately predicts driving performance (SDLP). Results Data from N = 604 driving tests (N = 96 participants) and corresponding psychometric tests was available for the statistical analysis. For the difference scores from placebo, a total of N= 431 comparisons could be made. Tables 1 and 2 show the correlations and their significance between differ- ence scores from placebo for SDLP and parameters of the psychometric tests. Best correlations are found for tracking and the divided attention test. However, the predictive validity of the parameter that correlates best with SDLP (tracking in the divided attention test) is only 22%. Data for individual drugs show comparable results, but not consistently. The relative small number of subjects for individual drugs may have had an impact on the observed correlations. Also, no clear dose– response relationship was observed. For example, performance on the tracking tests and tracking in the divided attention test correlated significant with SDLP of the low dose of bromfenac (25 mg) but not with SDLP of the high dose (50 mg). To determine whether a combination of test parameters would show a higher predictive validity to changes in