Pupil size reveals hidden cognitive fatigue

Researchers at the University of Tsukuba have identified a novel method to detect cognitive fatigue through pupil contraction. This discovery is particularly relevant in the realm of prolonged digital activities, such as esports, which demand high levels of mental exertion.

The study reveals that pupil diameter decreases as cognitive fatigue sets in, offering a measurable indicator of mental strain that is often unnoticed by the individual.

Addressing cognitive fatigue in esports

As digital interactions increasingly dominate our daily lives, balancing human performance and health between physical and digital realms has become a significant challenge.

While strategies for maintaining physical health are well-documented, methods for managing cognitive health during extended digital activities are still emerging.

Esports, a blend of physical and digital activities, often involve intense and prolonged mental engagement. Despite the cognitive benefits of moderate gaming, prolonged exposure can lead to adverse effects, including cognitive fatigue.

Focus of the study

The researchers set out to explore whether gamers can accurately sense their own cognitive fatigue and identify potential non-invasive indicators of this fatigue. They recruited 35 young adult participants from the University of Tsukuba and gaming communities in Akihabara, Japan.

The participants were divided into two groups: casual players, who played video games recreationally, and hardcore players, who engaged in competitive esports and often participated in tournaments.

Experimental protocol

The participants underwent a detailed pre-experiment protocol, including a body composition analysis and a survey to assess their gaming habits, physical activity levels, and sleep patterns.

On the day of the experiment, the individuals abstained from alcohol, caffeine, and strenuous exercise to ensure uniform physiological conditions.

The experiment was conducted in a controlled environment, with temperature and humidity standardized to 23°C and 50%, respectively. Participants played a virtual football game for three continuous hours in individual tents to maintain consistent visual stimuli.

During the gaming session, heart rates were monitored using a chest-worn heart rate sensor, and pupil diameters were measured using an eye tracker positioned at the bottom of the monitor. This setup allowed for real-time tracking of physiological responses without interrupting the gaming experience.

Declining cognitive performance

Cognitive performance was assessed using three specific tasks: the Flanker task, the Stroop task, and the Simon task. These tasks measured different aspects of executive function, such as reaction time and accuracy in response to visual stimuli.

Assessments were conducted before the gaming session and at hourly intervals to track changes in cognitive function over time.

In addition to cognitive tasks, participants completed questionnaires to gauge their subjective feelings of enjoyment and fatigue using visual analog scales.

Initially, casual players showed an improvement in executive function after one hour of gameplay, particularly in the Flanker task, which measures the ability to manage directional interference.

However, after two hours, both casual and hardcore players exhibited a decline in cognitive performance. This was evident in increased reaction times and decreased accuracy in cognitive tasks.

Interestingly, this cognitive fatigue did not align with the players’ subjective feelings of fatigue, suggesting a dissociation between perceived and actual cognitive states.

Cognitive performance and pupil size

The most striking finding was the significant decrease in pupil diameter after more than two hours of continuous play. This reduction in pupil size was consistent across both casual and hardcore players, indicating a decrease in physiological arousal.

Pupil diameter, controlled by the autonomic nervous system, can reflect changes in cognitive load and fatigue.

As cognitive fatigue set in, pupil diameter decreased, suggesting it could serve as a reliable indicator of mental exhaustion.

Implications for digital fatigue management

Despite observed cognitive fatigue and pupil constriction, there were no significant changes in heart rate or cortisol levels throughout the gaming session.

This lack of change in traditional stress markers implies that the cognitive fatigue experienced by the players was not accompanied by increased physiological stress.

Instead, the decrease in pupil diameter provided a more sensitive measure of cognitive fatigue.

Both casual and hardcore players reported increased enjoyment during the gaming session, which did not correlate with the onset of cognitive fatigue.

The sense of fatigue, as measured by subjective questionnaires, did not significantly increase until after three hours of play for casual players and remained relatively stable for hardcore players.

This disparity suggests that players may not be fully aware of their cognitive decline, potentially leading to overexertion without realizing it.

Pupil diameter as a marker for cognitive fatigue

The researchers concluded that pupil diameter is a promising non-invasive marker for detecting cognitive fatigue during prolonged digital activities such as esports. This finding is particularly relevant for developing strategies to manage digital fatigue and promote healthier gaming practices.

However, the study also had its limitations. The sample size was relatively small, and the experiment was conducted in a controlled environment that may not fully represent real-world conditions. Additionally, the study focused on a specific type of esports game – virtual football – and the results might differ with other game genres or in different contexts.

Future research could expand on these findings by exploring other types of digital activities, involving a more diverse participant pool, and testing in real-world settings.

Investigating the impact of different gaming conditions, such as competitive stress and social interactions, could also provide deeper insights into the dynamics of cognitive fatigue.

The study is published in the journal Science Direct.

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