reactiontime

Reaction time (RT) is the time between a stimulus and the initiation of a motor response. It is used to assess processing speed and the time course of cognitive operations. Early work in mental chronometry by researchers such as Donders laid the groundwork for comparing processing stages by recording RTs across tasks.

RT tasks are categorized as simple RT (one stimulus, one response) and choice RT (multiple stimuli, different responses). More complex variants include go/no-go and stop-signal tasks that measure response inhibition. Stimulus modality and response modality influence RT; auditory stimuli and simple motor responses typically yield shorter RTs than visual stimuli or complex movements.

Measurement and analysis: RT is typically recorded in milliseconds with computerized or specialized hardware. RT distributions are positively skewed; researchers often use median RT or apply ex-Gaussian modeling; outliers above a threshold or extreme lapses are excluded from analysis.

Factors: age, fatigue, attention, arousal, motivation, practice, stimulant drugs, sleep loss, and neurological or psychiatric conditions can alter RT. RT generally decreases with age in childhood, stabilizes in adulthood, and increases again in older adults. Individual differences are common.

Values: In healthy young adults, simple visual RTs commonly fall roughly in the 150–250 ms range; auditory RTs are often faster, around 140–200 ms; choice RTs typically fall in the 200–350 ms range.

Applications: RT is used in cognitive psychology, neuropsychological assessment, sport science, and human factors engineering. It serves as an index of processing speed, and reduced RT variability or abnormal slowing can indicate fatigue, sleep deprivation, ADHD, dementia, or other neurological conditions.