Cross-modal warning effects on reflexive and voluntary reactions.

Previous research has shown that warning signals can speed the onset of the startle-blink reflex. To relate this phenomenon to warning effects on voluntary reaction time (RT), the latencies of both reflexive and voluntary responses were measured for nine factorial combinations of warning and reflexogenic stimulus modalities. Previous failures to use factorial manipulations of warning (S1) and reaction (S2) stimulus modalities have led to conflicting results in both the reflex and RT literatures. Using psychophysically matched warning signals, we found a facilitation of reflex latency that was nonspecific with regard to S1 and S2 modality. Furthermore, there was no support for the widely held assumption that visual stimuli are inherently less alerting than auditory and cutaneous stimuli. A between-group comparison showed that simultaneous voluntary reactions do not distort the reflex facilitation effect. These results support the validity of reflex facilitation as a simple model system for studying warning effects on sensorimotor reactions.