Experimental psychologists have discovered that multiple factors affect a person's reaction time to stimuli including their age, gender and personality, as well as physical and mental state. Scientists differentiate between simple reaction times, which may be relatively fast, and complex reaction times, which involve recognition or choice.
Reaction time experiments have discovered that in most people, reaction time grows faster until around age 30, then slowly decreases. Thus, children and the elderly have slower reaction times than adults. In addition, men react faster than women in virtually every age group unless there are other factors present to change reaction time. Different experiments show that extroverted or anxious personalities have shorter reaction times, as do athletes and the physically fit.
Other, more temporary factors influence reaction time. Fatigue, illness and exposure to depressant drugs can significantly lengthen reaction time, while moderate doses of caffeine can shorten it. Subjects also tend to react faster to unpleasant stimuli such as bad smells, because these types of stimuli affect the survival instinct. Level of distraction is another factor affecting reaction time. If the stimulus is accompanied by background noise or visual distractions, the reaction time can be longer.
Studies involving more complicated reactions are often affected by other factors. When an individual is asked to recognize a particular stimulus, choose between stimuli or solve a problem, intelligence level becomes important. Additionally, people with learning disabilities or brain injuries react much slower.