Thesis, COLLÉGIALITÉ

Abstract

Introduction: Mental fatigue is a pervasive problem affecting cognitive performance, but its underlying mechanisms and effective measurement methods remain insufficiently understood. This study aims to examine the effects of cognitive load (high vs. low) and task duration (16 minutes vs. 32 minutes) on mental fatigue in healthy young adults using the Time Load Dual Back (TLDB) task. Methods: Participants were divided into three groups based on task modality: Group 1 (low cognitive load, 16-minute task), Group 2 (low cognitive load, 32-minute task), and Group 3 (high cognitive load, 32-minute task). Objective performance measures (accuracy, reaction time, signal detection theory metrics) and subjective fatigue levels (measured via the Visual Analogue Scale of fatigue, VAS-f) were recorded before and after the task. The impact of task duration and cognitive load on these measures were analysed across groups using statistical methods. The deltas of the measurement scores were calculated to evaluate the impact of the time between the start and end of the task. Evaluation of task duration and workload were performed using t-tests for independent samples. Analyses for subjective measures (VAS-f) were performed using repeated measures ANOVA followed by post-hoc tests to analyse the differences between the groups. Pearson correlations were used to correlate objective and subjective measures. Results: Regarding the analysis of the effect of task duration modulation on performance, changes in reaction times during the task were significantly different between groups. The shorter task duration was associated with faster reaction times. For performance changes based on workload, significant differences were observed between the high and low workload. Lower accuracy, as well as lower sensitivity and liberal response, were associated with the high workload. Reaction time was more significant in the long-duration, low-workload group. Measurements using the VAS-f showed a significant increase in scores between before and after the task for duration and workload analyses, with a significant interaction between time and group for the high workload. However, there were no significant results regarding group conditions. Correlation analyses for task duration showed no significant correlation between cognitive performance and VAS-f. Significant negative correlations were found for high workload between changes in accuracy and VAS-f. Conclusion: The study confirms that cognitive load is a key determinant of mental fatigue, with a higher workload leading to more pronounced declines in cognitive performance and a correlation with task accuracy and fatigue sensation. Task duration did not show significant differences between short and long durations. The TLDB task is validated as an effective tool for inducing and measuring mental fatigue in healthy young adults, except for reaction time, which showed contradictory results. Future research should explore more physiological and subjective measures to elucidate the underlying mechanisms of cognitive fatigue.