Microsaccade and drift dynamics reflect mental fatigue

Abstract

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 can modulate saccade dynamics, but its effects on 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 influence eye movements despite affecting 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 parameters moreover supports the hypothesis of a common generator for microsaccades and saccades. We conclude that changes in fixational and saccadic dynamics can indicate mental fatigue due to time-on-task, irrespective of task complexity. These findings suggest that fixational eye movement dynamics have the potential to signal the nervous system's activation state.

Saccadic Eye Movement Metrics Reflect Surgical Residents' Fatigue

“…Time-on-duty modulated the saccadic peak velocity-magnitude relationship in a manner consistent with previous observations in laboratory and non-health care scenarios. 21,30 A physiologically plausible explanation for the effects of fatigue on eye movements has been provided recently. 21,32,61 Changes in attentional processing (ie, due to fatigue) can affect the strength of excitatory connections from the frontal cortex to the brainstem reticular formation, 67 thus modifying the characteristics of the peak velocity-magnitude relationship.…”

“…17,18 Thus, the sensitivity and objectivity of work demand assessment in ecologically valid surgical scenarios remains a major challenge in the health care field. [19][20][21] Objective eye movement metrics have been used to differentiate novice from expert surgeons, to quantify and to study surgeons' scanning behavior, [22][23][24] to assess concentration during surgical performance, 25,26 and as a measure of laparoscopic surgical skills. 27 Fatigue resulting from manipulations of the sleep/wake cycle can alter eye movements [28][29][30] in nonsurgical scenarios, in particular, the saccadic magnitude/peak velocity relationship.…”

“…27 Fatigue resulting from manipulations of the sleep/wake cycle can alter eye movements [28][29][30] in nonsurgical scenarios, in particular, the saccadic magnitude/peak velocity relationship. 21,31,32 No research has investigated the effect of fatigue on the eye movements of health care professionals, however. Here, we set out to determine the effects of time-on-duty on the saccadic eye movements of surgical residents.…”

Distinctive features of microsaccades in Alzheimer’s disease and in mild cognitive impairment

“…Drift periods were defined as the eye-position epochs between (micro)saccades, overshoots, and blinks (Di Stasi et al 2013). We removed 10 ms from the start and end of each drift period because of imperfect detection of blinks and (micro)saccades, and we filtered the remaining eye position data with a low-pass Butterworth filter of order 13 and a cutoff frequency of 30 Hz (Murakami et al 2006;Di Stasi et al 2013).…”

“…We removed 10 ms from the start and end of each drift period because of imperfect detection of blinks and (micro)saccades, and we filtered the remaining eye position data with a low-pass Butterworth filter of order 13 and a cutoff frequency of 30 Hz (Murakami et al 2006;Di Stasi et al 2013). To calculate drift properties (such as mean velocity and duration), we used the filtered data described above and removed an additional 10 ms from the beginning and end of each drift period to reduce edge effects due to the filter.…”