An efficient, objective testing method and system for evaluating changes in mental function is described. The method and system are based on measuring an individual's behavioral responses and brain function during a brief cognitive test battery and passive control conditions. The method and system is designed to assess an individual's fundamental cognitive functions, and whether those functions have been significantly affected by a variety of factors such as progressive disease processes, medication, stress, fatigue, training, or the passage of time. The method and system can be used to determine whether drugs being evaluated to treat diseases or conditions affecting cognitive brain function have a significant positive effect on delaying or improving the symptoms of such a disease or condition, especially during clinical trials for drug approval and subsequent marketing. The method and system may also be employed as part of the successful diagnosis or ongoing treatment of neurological diseases or conditions that directly or indirectly affect human neurocognitive performance. The method and system may also be used to determine transitory changes in overall cognitive function due to emotional stress or fatigue, and more long lasting changes in overall cognitive function following training and educational programs.