Microsaccade and drift dynamics reflect mental fatigue during visual search
63.44, Wednesday, May 15, 8:30 am - 12:30 pm, Orchid Ballroom
Leandro L. Di Stasi1, 2, 3, Michael B. McCamy1, Andrés Catena4, Stephen Macknik5,1, Jose J. Cañas2, Susana Martinez-Conde1; 1Department of Neurobiology, Barrow Neurological Institute, Phoenix, AZ, USA, 2Cognitive Ergonomics Group, Faculty of Psychology, University of Granada, Spain, 3Joint Center University of Granada - Spanish Army Training and Doctrine Command, Spain, 4Learning, Emotion and Decision Group, Faculty of Psychology, University of Granada, Spain, 5Department of Neurosurgery, Barrow Neurological Institute, Phoenix, AZ, USA
Our eyes are always in motion. Even during periods of relative fixation, we produce so called "fixational eye movements", which include microsaccades, drift, and tremor. Mental fatigue and task difficulty can modulate saccade dynamics, but their effects on fixational microsaccades and drift are unknown. Here we asked human subjects to perform a prolonged and demanding visual search task (a simplified air traffic control task), with two difficulty levels, under both free-viewing and fixation conditions. Saccadic and microsaccadic velocity decreased with time-on-task, whereas drift velocity increased, suggesting that ocular instability increases with mental fatigue. Task difficulty did not affect eye movements, despite increased reaction times, performance errors, and subjective complexity ratings. We propose that variations in eye movement dynamics with time-on-task are consistent with the activation of the brain's sleep centers in correlation with mental fatigue. Covariation of saccadic and microsaccadic eye movements moreover supports the hypothesis of a common generator for microsaccades and saccades. We conclude that changes in fixational and saccadic dynamics indicate mental fatigue reliably during prolonged visual search, independent of task complexity. These findings have implications for the interpretation of current results and the design of future experiments in visual and oculomotor neuroscience.