Pupil size revealed to be a key indicator of cognitive fatigue

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A recent study published in the journal Computers in Human Behavior has discovered a novel way to detect cognitive fatigue through pupil contraction. This finding is particularly relevant in the context of prolonged digital activities, such as esports, which demand high levels of mental exertion. Researchers found that pupil diameter decreases as cognitive fatigue sets in, providing a measurable indicator of mental strain that isn’t always perceived by the individual.

Researchers at the University of Tsukuba sought to address a critical gap in the understanding of cognitive fatigue during digital activities, particularly esports. As digital interactions increasingly dominate our daily lives, balancing human performance and health between the physical and digital realms has become a significant challenge. While physical activity and nutrition strategies are well-documented for maintaining physical health, the strategies for managing cognitive health during extended digital activities are still in their infancy.

Esports represent a fusion of physical and digital activities, often involving intense and prolonged mental engagement. Despite the cognitive benefits of moderate gaming, prolonged exposure can lead to adverse effects, including cognitive fatigue. In their new study, the researchers aimed to explore whether gamers can accurately sense their own cognitive fatigue and to identify potential non-invasive indicators of this fatigue.

The researchers recruited 35 young adult participants from the University of Tsukuba and gaming communities in Akihabara, Japan. These 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.

The participants underwent a detailed pre-experiment protocol, including a body composition analysis and a pre-survey to assess their gaming habits, physical activity levels, and sleep patterns. On the day of the experiment, they were required to abstain from alcohol, caffeine, and strenuous exercise to ensure uniform physiological conditions.

The experiment was conducted in a controlled environment, with the 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, their heart rates were monitored using a chest-worn heart rate sensor, and their 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.

Participants’ cognitive performance was assessed using three specific tasks: the Flanker task, the Stroop task, and the Simon task. These tasks were designed to measure different aspects of executive function, such as reaction time and accuracy in response to visual stimuli. The assessments were conducted before the gaming session and at hourly intervals during the session 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. Mood states were also assessed using the Two-Dimensional Mood Scale, which measures various psychological states such as arousal and pleasure.

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 decline 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.

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 is controlled by the autonomic nervous system and can reflect changes in cognitive load and fatigue. The researchers found that as cognitive fatigue set in, pupil diameter decreased, suggesting it could serve as a reliable indicator of mental exhaustion.

Despite the 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.

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. The study highlights the importance of objective physiological measures over subjective self-assessments in understanding cognitive fatigue and its impacts on performance and health.

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, “Cognitive decline with pupil constriction independent of subjective fatigue during prolonged esports across player expertise levels,” was authored by Takashi Matsui, Shion Takahashi, Genta Ochi, Seiji Yoshitake, Daisuke Funabashi, Hiroki Matsuoka, Junichi Kagesawa, Shohei Dobashi, Hisashi Yoshimoto, Yosuke Sakairi, and Hideki Takagi.

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