Subjective difficulty of movements with ongoing visual control

Objective difficulty of a single-component visually controlled movement may be defined by Fitts's (1954) Index of Difficulty, which is a measure of difficulty in the sense that movement time is linearly related to the objective measure. For movements that have multiple components, it becomes difficult to determine an objective measure of task difficulty due to unknown interactions between components of the movement and interactions with other factors. Thus, it may be necessary to use indirect methods for allocating a measure of task difficulty. The purpose of the study was to determine whether participants could validly construct a subjective measure of the movement difficulty and whether this measure was related to the known objective measure of difficulty. Experiments showed that for single-component movements, there was a close relationship between measures of subjective and objective difficulty. With two-component visually controlled movements it was found that subjective difficulty could be related to objective difficulty, but not as simply as for single-component tasks.