Planning macroscopic aspects of manual control: end-state comfort and point-of-change effects

A recent emphasis in motor control research is the planning of macroscopic features and how variables such as efficiency and comfort influence the planning process. This paper extends the work by Rosenbaum and Jorgensen (1992) by further studying the end-state comfort effect. In the first experiment, participants picked up a dowel using an underhand or overhand grip and touched one end to a numbered target on the wall. The height of the #9 target was set at the height of participants' right shoulder. The second experiment involved awkwardness ratings. Participants touched the 14 targets with the dowel as well as with a small dumbbell and the comfort of the end position was rated on a seven-point scale. In the third experiment, participants moved a dumbbell to the targets in the same procedure as the first experiment. Overall, the probability analyses indicated that as the end-state comfort effect was magnified, the sequential effect vanished and a distinct point-of-change effect appeared. Optimization theory and the knowledge model readily explained the phenomena of the end-state comfort effect, the sequential effect, and the point-of-change effect. The present findings indicate that comfort has a powerful influence on the planning of motor performance.