EYEBLINK CROSS-HABITUATION BETWEEN TACTILE AND ACOUSTIC SYSTEMS IN HUMANS

To study cross-habituation of the eyeblink reflex in humans, subjects were repetitively exposed to a blink-eliciting stimulus in one modalit y and then shifted to a second stimulus in a different modality. One g roup of subjects began with a tactile stimulus and switched after 40 t rials to an acoustic stimulus. The other began with the acoustic and s witched to the tactile. No evidence of cross-habituation was found in the shift from tactile to acoustic, suggesting that habituation takes place in the sensory limb of the reflex. Cross-habituation was found, however, in the shift from acoustic to tactile stimuli. This result wa s expected because the act of blinking to the acoustic stimulus activa tes trigeminal afferents from the eyelid; as a result, the tactile sti mulation from the blink to the acoustic stimuli had already begun habi tuation in the tactile pathway before the first external tactile stimu lus was received.