NOT LOOKING WHILE LEAPING - THE LINKAGE OF BLINKING AND SACCADIC GAZESHIFTS

Many vertebrates generate blinks as a component of saccadic gaze shift s. We investigated the nature of this linkage between saccades and bli nking in normal humans. Activation of the orbicularis oculi, the lid c losing muscle, EMG occurred with 97% of saccadic gaze shifts larger th an 33 degrees. The blinks typically began simultaneously with the init iation of head and/or eye movement. To minimize the possibility that t he blinks accompanying saccadic gaze shifts were reflex blinks evoked by the wind rushing across the cornea and eyelashes as the head and ey es turned, the subjects made saccadic head turns with their eyes dosed . In this condition, orbicularis oculi EMG activity occurred with all head turns greater than 17 degrees in amplitude and the EMG activity b egan an average of 39.3 ms before the start of the head movement. Thus , one component of the command for large saccadic gaze shifts appears to be a blink. We call these blinks gaze-evoked blinks. The linkage be tween saccadic gaze shifts and blinking is reciprocal. Evoking a refle x blink prior to initiating a voluntary saccadic gaze shift dramatical ly reduces the latency of the initiation of the head movement.