Increasing task difficulty during practice is not beneficial for motor skill retention

The optimal challenge point framework states that there is an optimal level of task difficulty that maximizes motor learning. According to this framework, task difficulty is not only influenced by the difficulty of the task itself, but also by the skill level of the individual performing the task. Because the level of a motor skill widely varies between people, it is conceivable that variation in skill affects motor learning outcomes on a group level. Therefore, the aim of the current study was to determine the effects of task difficulty on motor skill acquisition and retention, while controlling for individual skill level. We hypothesized that the difficulty of the task acts as a constraint for motor learning. When the performance requirements are reduced, the demands for task problem-solving diminishes and the available information for learning reduces, thereby reducing the amount of improvement with practice.
Healthy young participants (N=14) were trained to a similar skill level on a mirror star tracing task, after which they were randomly assigned to learn with either an easier (Easy group) or a more difficult (Hard group) task. The difficulty was defined by the width of the wall of the star and motor performance was measured in terms of speed and accuracy.
The results of this pilot study indicate that increasing the performance requirements during practice is not more beneficial for motor learning, since both groups improved to the same amount. This novel results are against our hypothesis, not in line with the challenge point framework, and are also in conflict with prior research emphasizing the benefit of enhanced task difficulty on motor learning. If confirmed, this preliminary results have important implications for learning a sports skill or re-learning a motor skill impaired by medical conditions such as stroke.