This study provided a detailed investigation of perceived difficulty (PD) in a Fitts task. The Fitts task has been used to study Fitts’s law, which shows that movement time (MT) is related to the information constraints of the movement (Fitts’s Index of Difficulty, ID) such that there is a positive, linear relationship between MT and ID and MTs are similar when the scale of the movement requirements vary but ID is equal (scale invariance). According to Fitts’s law, Fitts’s ID provides an index of objective difficulty; does Fitts’s ID also provide an index of subjective difficulty? The main goal of this study was to address this question. It was hypothesized that the characteristics of the MT-ID relation described by Fitts’s law extend to the PD-ID relation. This hypothesis was addressed in two experiments, both including a variety of ID and scale conditions. In Experiment 1, participants (N = 20) assessed performance difficulty in prospective action; in Experiment 2, participants (N = 40) assessed performance difficulty in imagined and actual action. The results from both experiments supported the hypothesis. The support was limited, however; under certain conditions, there was evidence of a non-linear PD-ID relation and scale variance for PD. Thus, within limits, Fitts’s ID provides an index of subjective difficulty in prospective, imagined, and actual action.
In Experiment 2, MTs were collected in addition to the PD judgments. It was hypothesized that MT is superior to ID in predicting PD and that MT mediates the relationship between PD and ID. The results supported these hypotheses for many participants in both action conditions, but particularly in imagined action. An additional finding was that participants’ PD judgments in imagined and actual action were very similar. In conclusion, participants’ PD judgments relate more to the outcome of their action experience (i.e., MT) than the information constraints of the action (i.e., ID). Furthermore, actual experience in the task, and the external feedback that accompanies actual experience, does not have much of an effect on participants’ PD judgments. It appears that internal feedback influences participants’ PD judgments in both imagined and actual action.