Pupil Dilation Fulfills the Requirements for Dynamic Difficulty Adjustment in Gaming on the Example of Pong

When games are too easy or too difficult, they are likely to be experienced as unpleasant. Therefore, identifying the ideal level of game difficulty is crucial for providing players with a positive experience during gaming. Performance data is typically used to determine how challenged a player is; however, this information is not always available. Pupil diameter has recently been suggested as a continuous option for tracking gaming appraisal. In this paper, we describe two experiments with in total 55 participants playing 'Pong' under four levels of difficulty. Difficulty was manipulated via ball-speed (Experiment 1) and racket-size (Experiment 2) ranging from under-to overload. Pupil dilation and appraisal were maximal under medium difficulty (compared to easy and hard levels). These findings demonstrate the usefulness of pupil diameter as basis for psychophysiologically dynamic difficulty adjustment as it is sensitive both to under- A nd overload, hence underlining pupil dilation's potential value for user-adaptive interfaces in general.