Effect of task difficulty and interstimulus interval on blink parameters.

The effects of task difficulty and interstimulus interval (ISI) on blink rate, blink latency and blink duration, were studied in a modified Sternberg memory task in which either two or six characters were to be memorized. Stimuli were presented in ISI blocks at either 5.3 or 9.3 s (SOAs of 6 or 10 s). While blink rate and blink duration declined prior to each stimulus, the difficulty of the expected task (the length of the memory set) did not affect the rate of decline or the final prestimulus level. Concerning ISI, blink rate declined more rapidly during shorter ISIs but the final prestimulus level, as was the case with task difficulty, was unaffected by the ISI duration. Presentation of the 6-character memory set produced a marked immediate inhibition of blinking. The data suggest that the encoding of visual stimuli is more akin to processes invoked in preparation for input than to ensuing processing stages since both encoding as well as preparation are accompanied by inhibition of blinking.