FUNCTIONAL-SIGNIFICANCE OF THE EARLY COMPONENT OF THE HUMAN BLINK REFLEX

The relationship between the size of the first electromyographic (EMG) component of the cutaneous blink reflex (Pi) and onset of eyelid clos ure in human adults was determined in 4 experiments in which R1 size w as varied by different means: change in stimulus intensity, paired sti mulation, and warning. Two-phase lid movements were frequently seen, w ith an early small movement followed by a large rapid movement. All ex periments showed that larger Rls were associated with shorter latencie s of both movements. This' covariation was general across participants and was independent of shifts in the excitability of the blink reflex pathways indexed by R1 latency, R2 latency, and R2 area (R2 is the mo re prolonged, later EMG component). The results indicate that Pt acts first to evoke an early lid movement and second to facilitate eyelid c losure by the later R2 burst. Identification of this second behavioral function for R1 aids the interpretation of other findings and encoura ges its use as a model system.