# Workload Assessment of Operators: Correlation Between NASA-TLX and Pupillary Responses
## 5 Discussion  
Our study supports our initial three hypotheses. We observed a significantly positive correlation between the NASA-TLX scores and the original mean pupil size from the overall dataset. The tasks involving complex eye-hand coordination in the laparoscopic setting exhibited significantly higher workloads reflected by both the NASA-TLX scores and the pupil size measurements compared to the visual tracking tasks. In addition, task repetition was found to decrease pupil size and the NASA-TLX scores, but not the original mean pupil size in the laparoscopic task. The synchronized changes between the NASA-TLX scores and pupillary responses provided strong evidence that well-designed paper-based tools, along with pupil size measurements, can reliably assess operator workload when used appropriately. Pupillary response is part of the sympathetic nervous system activation; as the workload increases, the sympathetic activity rises, leading to physiological responses such as increased heart rate, respiration, and pupil dilation [44; 45]. Although measuring eye-tracking bio-signals is a logical approach to assessing workload, it requires specialized equipment that must be attached to operators. The interference caused by these devices can limit their use in certain situations, such as during surgery [46]. Therefore, paper-based tools alone still offer a reliable workload assessment in that situation. We are glad to see that both NASA-TLX and pupil dilation successfully reported significant differences in two tasks with different difficulty. To make the data comparable, we maintained consistent environmental conditions for both the tasks to eliminate confounding variables such as room illumination and environmental interference. This control ensured that the changes in pupil size were due to the tasks rather than external factors. The significantly higher NASA-TLX scores and pupil sizes associated with visuomotor tasks were consistent with cognitive load theory. Motor control requires additional cognitive resources beyond visual processing alone, resulting in higher workload and consequently higher NASA-TLX scores and pupil sizes [47; 48]. Task repetition had significant effects on most of the workload measures, except for the original mean pupil size during the laparoscopic task. Repeating the laparoscopic task did not result in noticeable changes in the original mean pupil size. This lack of change may be attributed to the high difficulty inherent in the laparoscopic procedure and suggests that the original pupil size is less sensitive than the baseline-adjusted pupil size. In contrast, repetition of the visual tracking task led to significant changes in both the original and adjusted pupil sizes. This can be explained by the fact that tracking a moving arrow is a common activity, allowing participants to achieve proficiency and automaticity after only one repeated trial. Moreover, performance showed significant improvement in both the tasks, indirectly confirming that repetition reduces trainee workload. These findings are consistent with prior studies demonstrating the effect of practice in reducing workload [49]. A detailed inspection on pupillary response, this study found that the NASA-TLX scores correlated only significantly with the original mean pupil size, showing a trend but not a significant correlation with the adjusted pupil size. However, thee adjusted pupil size was more sensitive in characterizing the effect of task repetition, suggesting that precautionis needed when applying pupillary response to assessing workload, as it can be influenced by many other variations. One limitation of this study is that NASA-TLX assessments were not conducted between the trials during the visual tracking task. As a result, this study was unable to evaluate how repetition affects NASA-TLX scores in this context. However, previous studies have shown significant improvements in participants' performance between trials, suggesting that trainees did experience reduced workload in the visual tracking task.