Abstract
Flow, which is a rewarding state of full focus, typically arises when engaging in tasks with an optimal level of difficulty that is matched with a person's skill level. Meanwhile, optimal task difficulty usually comes with the greatest effort exertion. We propose that not only the difficulty level, but also the level of effort invested plays a role in the subjective feelings of flow. Using a visual discrimination task, we manipulated stimulus complexity and the expected probability of detecting a difference to induce and disentangle perceived task difficulty and effort exertion, respectively. Notably, perceived task difficulty increased proportionally with increasing stimulus complexity. Reaction time as an index of effort exertion, increased in challenging tasks with higher expectancy. Patterns of flow experience mirrored the observed shifts in effort exertion, suggesting a possible link between flow and effort. However, no parallel trend emerged in the physiological flow indicator, specifically the P300 amplitude. These findings highlight the intricate interplay between subjective experiences of task difficulty, exerted effort, and the subjective sense of being in 'flow'.