Reaction time to the onset and offset of electrocutaneous stimuli as a function of rise and decay time

Sticht, Thomas G.; Foulke, Emerson · 1966 · OpenAlex-citations

DOI: 10.3758/bf03207409

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Summary

This study investigates how the rise and decay times of electrocutaneous stimuli influence reaction times (RTs) to stimulus onset and offset. Motivated by earlier findings that onset RTs are typically faster than offset RTs, the authors sought to test the hypothesis that this discrepancy arises from neural adaptation. Specifically, they examined whether varying the rate at which stimulus intensity increases or decreases could alter the initial burst of nerve impulses associated with abrupt onsets, thereby affecting RT differences. The experiment involved three male college subjects who performed 1,000 practice trials before the main study. Stimuli consisted of 70-cps sinusoidal electric currents applied to the left index finger. The researchers manipulated two variables: five rise/decay times (0.5, 5, 26, 140, and 340 msec) and five intensity levels (2, 4, 6, 8, and 10 dB above each subject’s offset threshold). Subjects reacted to stimulus onset by releasing a telegraph key and to offset by depressing a footswitch, with RTs measured to the nearest millisecond. Each subject completed ten experimental sessions, yielding 40 onset and 40 offset RTs for each stimulus combination. Results demonstrated that both onset and offset RTs increased linearly as rise and decay times increased. With short ramp times, onset RTs were faster than offset RTs, consistent with the neural adaptation hypothesis. However, as ramp times lengthened, this difference diminished until onset and offset RTs became equal at a specific "on=off ramp time," which varied by intensity. Unexpectedly, at longer ramp times, offset RTs became faster than onset RTs. Additionally, RTs for both onset and offset decreased as stimulus intensity increased. The study identified a critical intensity threshold for each ramp time, below which onset RTs were faster and above which offset RTs were faster. The authors interpret these findings through the lenses of neural adaptation and accommodation. The initial burst of impulses at rapid onsets explains faster onset RTs, while adaptation reduces impulse frequency during sustained stimulation, slowing offset responses. The unexpected reversal at long ramp times is attributed to accommodation, where gradual onsets elevate the neural threshold and reduce the number of responsive fibers. The authors propose that three factors delay onset responses (delayed threshold, fewer active fibers, slower impulse rate increase), while only two retard offset responses, explaining why offset RTs can become faster under specific conditions. This work clarifies the physiological mechanisms underlying sensory detection and reaction timing.

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