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.

Stimulus duration as an age-dependent factor in reflex blinking.

Alternative hypotheses of differential development of auditory and visual systems versus temporal-processing systems were tested to explain prior adult-infant differences in reflex blink latency. The present study removed a confound between stimulus modality and duration, present in prior work, and determined whether age interacted with modality or with duration when they were varied orthogonally. Reflexes were elicited from human adults and infants under 4 stimulus conditions: flash and click, delivered singly and in trains. Age interacted only with duration to affect latency and elicitation probability, reflex characteristics which depend on adequate triggering by a transient change at onset. In contrast, age did not interact with duration to affect peak amplitude which presumably depends on temporal integration. Findings are compatible with the hypothesis that processes or structures, specialized for differentiation of transient stimulus change, mature at a different rate than those specialized for integration of stimulus energy over time.