By Ning Li

Look out! There’s a guy crossing the road!” John’s brain shouted to him. Almost instantly, he hit the brakes of the car and swerved to the right to avoid hitting the pedestrian. “Well done; your reaction time is average,” said the computer. In everyday life, quick reaction time is necessary to avoid unnecessary accidents. Since it is such an important part of life, one should understand how the brain works and its limitations. The reaction time of a person can be divided into different parts based on what he sees, feels, or hears. This paper aims to help the reader better understand reaction time.

The three main divisions of reaction time are mental processing time, human movement time, and device response time. Mental processing time is the length of time taken by the driver to see or hear something and decide the best way to respond. Mental processing can be further divided into four subcategories: sensation, perception or recognition, situational awareness, and response selection and programming.

Sensation is the time taken for the driver to realize that there is an object on the road. The size, brightness, loudness, etc. of the object affects the processing time. Therefore, a driver seeing a bigger, brighter object will react faster as compared to seeing a smaller, darker object. The time taken to recognize the object (a person, vehicle, animal) is perception or recognition. Situational awareness is the time the driver takes to comprehend the scene. The driver takes time to understand that the object is in his way and a collision may result unless he takes evasive action. Response selection and programming is the time taken for the driver to take the necessary action to avoid hitting the object. Electrophysiological studies or the study of biological cells and tissue have shown that the decision-making time happens faster than anything on earth can record.

After the object is seen, processed, and the driver has decided on a course of action, the driver must activate his muscles to perform the required movement. As an example, if the driver decides to apply the brake, the brain has to tell the muscles of the foot to release the accelerator pedal, shift to the brake pedal, and depress it.

The last division is device engagement time. The devices (car brakes) take time to engage. The forces of nature (gravity, inertia, etc.) also affect the device. Response speed varies in activities, people, and places. Therefore, there is no set reaction time for human beings as human reaction time can only be averaged to be about 200 milliseconds.

Reaction time can also be affected by other factors such as age, gender, and visibility. Multiple researchers have found that older people have a slower reaction time than younger people. However, failure to define “older” creates several issues with the information. An experiment done by Midwood High School showed that, between teachers and students, the students’ reaction times were faster.

Gender is another factor that affects reaction time. Females appear to have a slightly slower reaction time than males. However, females have a more appropriate reaction than males. In other words, males react faster than females but females’ reaction to the circumstance is usually the more appropriate one.

Visibility is another factor that greatly affects reaction time. Low contrast, as well as bad weather,  affects drivers’ reaction times. Low light is not necessarily a hindrance to reaction time and can improve if the object is bright. However, too much reflection off an object in bright light can reduce reaction time. Hence, many different factors must be taken into consideration before judging a person’s reaction time.

In our life, reaction time is extremely important. Every activity has different factors that affect reaction time. However, although the reaction time may vary, the principles that stand behind the numbers in reaction time always stay the same.

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Sources Consulted

“Fingertip Reaction Time.”

Marc Green. “Driver Reaction Time.”

“Mental Chronometry.”

“Reaction Time Statistics.”

“Reaction Time Test.”

“What Factors Affect Human Reaction Time?” <> (accessed 3/21/2011)