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Sheng Tong Lin, Larry Allen Abel; Ocular motor fatigue induced by prolonged visual display terminal (VDT) tasks. Journal of Vision 2011;11(11):515. doi: https://doi.org/10.1167/11.11.515.
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The use of Video/Visual Display Terminals (VDTs) for monitoring work has increased in many industries since its first introduction in 1970s. Monitoring work, for example radar operation and factory quality control, is usually monotonous and performed on extended basis for hours, leading to visual fatigue. Depending on the criticality of the job, a few seconds delay as a result of fatigue might be crucial, for example in the case of radar operators. This study examines the possibility of using saccadic eye movements and pupillary dynamics as visual fatigue indicators in extended visual search. Thirty-nine subjects were instructed to perform boring visual search tasks for an hour using a computer screen. Eye movement and pupil size data are broken down into 12 time-blocks of 5 minutes each for analysis against time. Linear regression shows a significant gradual decrement trend in average saccadic velocity during the experiment (R2 = 0.58, F(1, 10) = 13.73, p < 0.01). The study also demonstrates a very strong relationship between reduction in pupil size fluctuation and time into the experiment (R2 = 0.82, F(1, 10) = 44, p < 0.01). While visual search performance is not affected, the regression results is consistent with the result from the subjective visual fatigue and sleepiness survey which indicates that subjects are significantly more visually tired at the end of the experiment. Our study therefore suggests the possibility of using average saccadic velocity and pupil size fluctuation across time as the indicators of fatigue. Future validation studies should extend the duration and increase the demand of the visual search task, allowing ocular behaviours to be captured at the point where fatigue has affected visual search performance.
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