There are many factors that can affect human reaction time. Reaction time is the time taken between a sensory stimulus appearing or occurring and the person involved making a response. This happens constantly in every day life often subconsciously from avoiding people and objects when walking to obeying traffic signals.
Scientists generally measure reaction times in three kinds of way. The first is simple reaction where one response is expected to one stimulus, for example pushing a button when a light comes on.
Secondly there are recognition tests where some of the stimulus should be reacted to and other stimulus ignored. Responding to the correct symbol or colour would be one example of this; there is still only one correct response.
Thirdly there is choice where the person reacting to the stimulus must do so in a way that corresponds to the stimulus. An example of this would be pressing the same key on a keyboard as appear on the screen.
Scientists use these to see how various factors affect human reaction time, common uses for this is for investigations into road safety or sports reaction times. There have been a few studies in recent years for example investigating the effects using a cell phone either hand held or hands free have on reaction time. Simply put will this distraction cause reactions times to increase adversely?
Here are some of the common factors that are found to adversely affect reaction times one way or another, these are by no means complete and can vary greatly depending on the subject matter involved.
Arousal or state of attention affects reaction times, and this also includes muscular tension. The slowest responses are when the subject is too relaxed or tense, the best response times are found somewhere in-between.
Relevance of the stimulus to survival also affects reaction time, a potentially life threatening situation is more likely to elicit a rapid response then a more mundane situation.
Age is another factor affecting reaction time reaction times generally shorten from birth to around the late twenties; they then decrease slowly with age. The decline of reaction time increases as a person reaches their seventieth year and beyond. Opinions vary as to why this is from mechanical factors such as a slower nervous system to older people generally taking more time and care in their decisions.
If the stimulus is visual whether it is seen directly or in your peripheral vision affects how fast you respond. Stimulus seen directly is reacted to faster then stimulus seen in the peripheral vision.
Practising or repeating a response improves reaction times, for example sports people practising for their chosen sport. This practise must be maintained however or the gains in shorten reaction times will be lost. It is also the reason why drills are effective.
Tiredness and fatigue both slow reaction times, mental fatigue is worse and this includes sleep deprivation both greatly increasing reaction times (and why it is advisable not to drive whilst tired).
Distractions such as other sensory stimulus such as background noise or being engaged in another task decrease reaction times. This is why even with a hands free kit it is advisable not to use your cell phone whilst driving, the distraction will slow your reaction time.
Physical fitness has an direct effect on reaction time the fitter a subject is the more likely they are to have a fast response time. Another reason to get down to the gym. Overall these and many other unforeseeable factors can have an affect on human reaction time whether they affect the mental or the mechanical aspects of human physiology.