Prepulse effects on the photic eyeblink reflex: evidence for startle-dazzle theory.

Weak visual prestimulation effects on the early (R50, 50-80 ms) and late (R80, 80-200 ms) components of the eyeblink response to bright light flashes were studied in 16 normal individuals. At a lead time of 120 ms, R50 was inhibited relative to no-prepulse control trials, whereas R80 was facilitated. According to the proposed startle-dazzle theory, luminance onset transients trigger an initial response, R50, that is functionally related to startle. Sustained stimulation then activates prolonged eyelid (R80) and pupil responses, which serve to minimize retinal bleaching. Although the sensitivity of the photic blink reflex to attention is controversial, R50 latency showed a pattern suggestive of inhibition of return (Posner & Cohen, 1984, Attention and performance, Vol. X, pp. 531-556, Hillsdale, NJ: Erlbaum). Analyses in a patient with unilateral occipital lobe damage supported previous evidence that inhibition by a visual prepulse requires neocortex, but facilitation does not.