The interactive effect of achievement motivation and task difficulty on mental effort.

The interactive effect of achievement motivation and task difficulty on invested mental effort, postulated by Humphreys and Revelle [Humphreys, M.S., Revelle, W., 1984. Personality, motivation, and performance: a theory of the relationship between individual differences and information processing. Psychol. Rev. 91, 153-184], was examined using behavioral, subjective, and effort-related physiological measures. Eighteen approach-driven participants and 18 avoidance-driven participants were selected based on their motive to achieve success scores and their motive to avoid failure scores. A 2x3 factorial design was used, with three levels of task difficulty. As expected, approach-driven participants performed better and had a stronger decrease of midfrequency band of heart rate variability than avoidance-driven participants, especially during the difficult task. These results support the interactive effect of achievement motivation and task difficulty on invested mental effort.