Glissadic saccades: a possible measure of vigilance

Eight males and eight females participated in a 60-min visual signal detection task requiring saccadic eye movements. The waveforms of saccades were evaluated in terms of glissades, slow eye movements in saccade initiation and termination, as a function of time-on-task. Saccades were categorized as anticipatory, stimulus-elicited, and return saccades; as well as blink-concurrent versus blink-free. The results showed that, for blink-free saccades, the occurrence of glissadic saccades increased with time-on-task for anticipatory and return saccades, but not for stimulus-elicited saccades. Likelihood of blink-concurrent glissadic saccades did not change over time-on-task. The results suggest that an increase in anticipatory and return glissadic saccades over time-on-task may be an index of vigilance decrement.