In a warned Go/No-Go reaction time experiment blink reflexes were elicited electrically immediately before, at, and shortly after the onset of a low intensity acoustic warning stimulus. This provided the opportunity to study the mutual effects of two stimuli of different modalities arriving at the facial nucleus. The warning stimulus was followed after 3 s by an acoustic response stimulus. Sixteen subjects participated in the experiment. They were informed by the response stimulus if a response (a voluntary blink of the right eye) was required. R1 magnitude was increased from 10 ms to 100 ms after warning stimulus onset, with a pronounced peak at 50 ms. The bilateral late component R2 was enhanced when the reflex eliciting stimulus preceded the warning stimulus. Between 20 ms and 30 ms after warning stimulus onset, R2 returned to control level, whereas an eliciting stimulus presented 40 ms or later after warning stimulus onset produced a pronounced inhibition. R2 latency was facilitated immediately after warning stimulus onset. It was concluded that the mutual effects of stimuli of different modalities can be interpreted only if the moment of arrival at the motor nucleus is taken into consideration.

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SUMMARY Blink reflexes were studied in 40 subjects at rest and during the performance of a task. The early reflex (R 1) showed an increase of amplitude of action potential during the task, the late reflex (R2) did not. The latency of RI did not change within the 45 minute test period; R2 showed an increase of latency during task. R1 showed a systematic decrease in amplitude within rest and task periods, presumably because of habituation. R2 amplitudes decreased throughout the whole experiment, independent of task or rest.

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