Dannewitz, a small number of previous studies suggest some antidepressants can negatively affect individuals' cognitive performance, impairing memory and reducing reaction time.

Many controlled trials have examined the effects of caffeine on the brain, demonstrating that caffeine can improve mood, reaction time, memory, vigilance and general cognitive function.

Cell phone conversation while driving creates "inattention blindness," a cognitive state that slows a driver's reaction time and limits his ability to detect changes in road conditions.