How are cognitive and physical difficulty compared?

Tasks that require less physical effort are generally preferred over more physically demanding alternatives. Similarly, tasks that require less mental effort are generally preferred over more mentally demanding alternatives. But what happens when one must choose between tasks that entail different kinds of effort, one mainly physical (e.g., carrying buckets) and the other mainly mental (e.g., counting)? We asked participants to choose between a bucket-carrying task and a counting task. Our participants were less likely to choose the bucket task when it required a long reach rather than a short reach, and our participants were also less likely to choose the bucket task the smaller the final count value. We tested the hypothesis that subjective task durations provided a common currency for comparing the difficulties of the two kinds of tasks. We found that this hypothesis provided a better account of the task choice data than did an account that relied on objective task durations. Our study opens the door to a new problem in the study of attention, perception, and psychophysics-judging the difficulty of different kinds of tasks. The approach we took to this problem, which relies on two-alternative forced choice along with modeling the basis for the choice, may prove useful in future investigations.