Mental Fatigue Induced through an Adaptive Paradigm: Effects on Parasympathetic Function and Attentional Engagement: Proceedings of the 22nd World Congress of Psychophysiology of the International Organization of Psychophysiology

Mental fatigue impairs performance and safety, yet its underlying psychophysiological mechanisms remain unclear. This study examined Heart Rate Variability metrics reflecting parasympathetic function and prefrontal activity (RMSSD and normalised high-frequency [nHF]), along with eye blink rate and flurries to capture attentional engagement.
Seventy-two adults completed six tasks across three executive function domains (inhibition, updating, switching) and two stimulus modalities (verbal, non-verbal). We recorded subjective and behavioural data related to perceived cognitive workload and fatigue, alongside ECG and EOG signals. In a repeated-contrast design, task conditions were manipulated across three groups: A (lower executive load, static difficulty), B (higher executive load, static difficulty), and C (higher executive load, adaptive difficulty). Static difficulty employed a practice-determined speed, whereas adaptative difficulty further adjusted it based on real-time performance.
ANOVA planned contrasts revealed that higher load alone (group B vs A) did not increase task-related perceived workload, but it did when combined with difficulty adaptation (group C vs B). After the six tasks, subjective fatigue had increased by 61% across all groups. Notably, groups with lower load (A) and difficulty adaptation (C) experienced fatigue faster than their comparison group (B) due to faster task pace that shortened overall task duration. Lower load with faster pace (group A vs B) was followed by 66% more blink flurries, while difficulty adaptation (groups C vs B) was followed by 15% less nHF and 79% more blink flurries relative to baseline.
While task pace influences attentional engagement, reflected by ocular fatigue compensation, fatigue under adaptive high executive load leads to parasympathetic withdrawal, suggesting reduced prefrontal activity. This study demonstrates that mental fatigue onset can be accelerated under sustained, adaptive high workload, consistent with cognitive over-stimulation. It also introduces a time-efficient approach to fatigue research, reducing the likelihood of inducing fatigue through prolonged cognitive under-stimulation.