Definition and Measurement Principle
Simple reaction time (SRT) measures how quickly a person responds to a single, predetermined stimulus with a single, predetermined action. A classic example is pressing a button the moment a light appears on screen. Since no discrimination between stimuli is needed, SRT captures the shortest possible path from perception to motor output. The measured value encompasses peripheral nerve conduction velocity, synaptic transmission efficiency, and muscle contraction onset time, with virtually no cognitive decision-making involved.
Typical Values and Sources of Variation
Healthy adults produce SRT values of approximately 180-200ms for visual stimuli and 140-160ms for auditory stimuli. Auditory reactions are faster because the pathway from the cochlea to the brainstem is shorter than the visual processing chain. Key factors influencing individual differences include age, arousal level, body temperature, and caffeine intake. Aging adds roughly 5-10ms per decade, primarily due to myelin sheath degradation and reduced nerve conduction velocity. A circadian pattern also exists, with fastest responses occurring in the afternoon when core body temperature peaks.
Applications and Limitations in Cognitive Testing
In Bench's reaction time tests, SRT serves as a baseline measurement. Subtracting SRT from choice reaction time isolates the cognitive processing cost of stimulus discrimination and response selection. An unusually slow SRT may indicate sleep deprivation or attentional lapses. However, SRT captures only one facet of cognitive performance and correlates weakly with intelligence or decision-making ability. Additionally, anticipatory responses - where participants press the button before the stimulus appears by learning timing patterns - can contaminate measurements, making randomized inter-stimulus intervals essential for accurate assessment.