Alerting effects on choice reaction time and the photic eyeblink reflex.

To test the possibility that a common mechanism might be responsible for alerting effects on voluntary and reflexive reactions, choice reaction times (RT) to intense flashes of light were compared with eyeblink reflexes simultaneously evoked by those stimuli. An acoustic accessory stimulus, irrelevant to the RT task, facilitated both voluntary and reflexive reactions. A time uncertainty manipulation also generated facilitation of both responses under conditions in which phasic arousal was presumably greatest. However, there were several dissociations between alerting effects on voluntary and reflexive reactions and between effects on the early and late subcomponents of the photic orbicularis oculi reflex. In conjunction with other research in humans and animals, these data support the assumption that alerting involves the activation of multiple neuromodulatory (e.g. monoamine) systems, each of which is characterized by a distinct behavioral, neuropharmacological, and electrophysiological profile.