Author(s): BENRAISS, A., LORCERY, A., GIRAULT, A., ANDRÉ, N., BERNARD, O., AUDIFFREN, M. , Institution: CENTRES DE RECHERCHES SUR LA COGNITION ET L’APPRENTISSAGE, Country: FRANCE, Abstract-ID: 1204

Introduction
Cognitive effort refers to mental resources allocated to tasks requiring sustained attention, concentration, and active information processing. It is essential for complex functions such as problem-solving, decision-making, memory updating, and attentional control. Engaging in cognitively demanding tasks for extended periods can be mentally exhausting, as it places significant demands on executive functions and may lead to mental fatigue. The more complex, unpredictable, or unfamiliar a task is, the greater the cognitive effort needed to maintain performance. In mental fatigue research, cognitive effort plays a central role, as prolonged engagement in demanding tasks is linked to declining performance and impaired cognitive control. However, the underlying neural mechanisms remain poorly understood. This study examines how sustained cognitive effort affects behavioral and neurophysiological responses, focusing on event-related potentials (ERPs) and subjective perceptions of motivation, fatigue, boredom, and drowsiness.
Methods
Seventy participants completed a 30-minute Dual 2-back (D2B) task consisting of 1,100 trials, requiring visual and visuospatial working memory updating. In each trial, a geometric figure appeared at the center, with a dot randomly positioned around it (8 possible positions). Either the figure or the dot was randomly colored red. If the dot was red, participants indicated whether its position matched that of trial n-2; if the figure was red, they determined whether it was the same as in trial n-2. Responses (Yes/No) were made using two buttons. EEG activity was recorded from 64 channels to analyze event-related potentials (ERPs) and examine mental fatigue in relation to behavioral data and self-reported cognitive states.
Results
The behavioral and EEG data recorded over 30 minutes were segmented into four periods of 7.5 minutes each. Analysis of reaction times (RT) for correct responses revealed a significant decrease for "No" responses, while remaining stable for "Yes" responses throughout the task. Additionally, the error rate remained stable for "No" responses but significantly increased for "Yes" responses. Furthermore, d-prime, an index of discrimination between trials n and n-2, decreased over the course of the task. Finally, analysis of event-related potentials (ERPs) showed a significant decrease in the amplitude of the P300 component. This decrease was not correlated with any behavioral or subjective data.
Discussion
This study highlights the impact of prolonged cognitive effort on performance and neural activity. A decrease in d-prime and an increase in errors for "Yes" responses suggest a decline in stimulus discrimination. The reduction in P300 amplitude reflects diminished attentional and working memory resources. However, this decrease was not correlated with behavioral or subjective measures. This result tends to put into perspective the role of motivation in explaining the decline in performance.