INTRODUCTION: Mental fatigue (MF) is a psychobiological state characterised by feelings of tiredness and lack of energy and caused by prolonged and demanding cognitive activity. There is evidence that MF can affect physical performance through impaired cognitive control; however, most studies have focused on endurance and strength in sports. In this study, we used a psychomotor shooting task requiring attentional control and response inhibition and measured behavioural performance and concomitant visual behaviour as an index of visual attention. We also evaluated mental fatigueinduced changes to the capacity to inhibit selective information.
METHODS: Sixteen participants visited the lab on two different days. On the experimental day, they completed a 50-minute computer task requiring selective visuospatial inhibition (Flanker task) to induce mental fatigue. On the control day, they viewed a 50-minute documentary. Before and after the fatiguing protocol (or the documentary), we assessed self-report MF (VAS and Fatigue-Fatigability) and inhibition performance at two computer tasks (Stop-Signal and Simon tasks). After the fatiguing protocol (or the documentary), we measured self-control capacity (State Self Control Capacity Scale), selfreport motivation as the willingness to engage in more of the computer tasks or more of the shooting task (bespoke questions), and psychomotor shooting performance as the number of civilians-casualties (on whom firing should have been inhibited) along with the visual behaviour through mobile eye tracking (EyeLink® II).
RESULTS: After the fatiguing protocol, self-control capacity was lower (p=0.020), fatigability was higher (p=0.015), motivation to engage in more of the computer task was lower (p=0.029), and the pre-to-post drop in energy level was more pronounced (p=0.014) compared to the control documentary. Despite these self-report differences, shooting performance, fixation, and saccade parameters did not differ between the fatiguing protocol and the documentary (p>0.05), nor did the pre-to-post changes in inhibition task performance (p>0.05).
CONCLUSION: Despite the participants feeling more fatigued after the fatiguing protocol as expected, their inhibition capability, shooting performance, and visual attention were not impaired compared to the control documentary condition. These null effects might be due to the participants’ eagerness to engage in anything else (but especially in such an attractive task as simulated shooting) after performing nearly 1 hour of the same activity (Flanker task or documentary). It may also be that the documentary induced boredom, and that prolonged engagement with it required participants to exercise self-control, which in turn could have produced mental fatigue. Finally, the participants may have exerted greater effort to compensate any detrimental effect of mental fatigue on cognitive and psychomotor performance. We encourage future research to test these interpretations.