Workload Assessment of Operators: Correlation Between NASA-TLX and Pupillary Responses

Abstract

Operators in high-stress environments often face significant cognitive demands that can impair their performance, underscoring the need for comprehensive workload assessment. This study aims to study the relationship between subjective self-reported measures, the NASA task load index (NASA-TLX), objective bio-signal measures, and pupillary responses. The participants engaged in either a visual tracking task or a laparoscopic visuomotor task while their eye movements were recorded using a Tobii Pro Nano eye tracker (Tobii Technology Inc., Stockholm, Sweden). Immediately after completing the tasks, participants provided NASA-TLX scores to assess their perceived workload. The study tested three hypotheses: first, whether increased pupil dilation correlates with higher NASA-TLX scores; second, whether task type affects workload; and third, whether task repetition influences workload. The results showed a moderate positive correlation between pupil size and NASA-TLX scores (r = 0.513, p < 0.001). The laparoscopic surgery task, which requires visuomotor coordination, resulted in significantly higher NASA-TLX scores (t = –6.23, p < 0.001), larger original pupil sizes (t = –22.57, p < 0.001), and more adjusted pupil sizes (t = –22.57, p < 0.001) than the purely visual task. Additionally, task repetition led to a significant reduction in the NASA-TLX scores (t = 2.86, p = 0.005), the original mean pupil size (t = 5.50, p < 0.001), and the adjusted pupil size (t = 6.34, p < 0.001). In conclusion, the study confirms a positive correlation between NASA-TLX scores and pupillary responses. Task type and repetition were found to influence workload and pupillary responses. The findings demonstrate the value of using both subjective and objective measures for workload assessments.