Effects of caffeine, methylphenidate, modafinil and placebo on cognitive performance of chess players in chess games and neuropsychiatric standardized tests. We hypothesize that substances will change cognitive performance in chess players leading to changed results in chess games and neuropsychiatric tests.

Inclusion Criteria:

• male
• 18-60 years old
• existence of ELO-number

Exclusion Criteria:

• physical diseases (e.g. diabetes mellitus, etc.) with necessity of using prescription drugs
• psychiatric diseases (e.g. psychosis, bipolar disorders, etc.) with necessity of using prescription drugs
• addiction of psychoactive substances
• smoker or quitter (< 5 years)
• use of more than 5 cups of coffee per day
• irregular day-night-rhythm (e.g. shift workers)