Now you see me, now you don't: Adapting practice through target exclusion negatively impacts motor learning.

How to optimize practice through scheduling of different task components or skills is a question that has received a lot of attention in motor learning research. Consistently, schedules with high variability in the order that skills are practiced elicit better learning outcomes than schedules with low variability. Another idea is that learners should seek to reduce the uncertainty of practice outcomes, by avoiding well-learned, low error components in acquisition. To test this idea, we used a target exclusion method to prevent learners from returning to task components with low error and studied how individuals given choice over practice choose to allocate time to components of varying difficulty. In a multi-target adaptation paradigm, we compared exclusion with no exclusion methods in random-schedule, self-control and yoked, matched-schedule groups (6 groups total). To manipulate uncertainty, we excluded targets from practice once participants attained a criterion error score (mean < 5) from the last 5 trials to the same target. Contrary to our predictions, groups that practiced without target exclusion were more accurate in retention compared to exclusion groups; irrespective of practice schedule. Self-control groups adopted uncertainty-based practice, spending more time at difficult targets and less time at easier targets. However, there were no group differences in error, based on schedule-type (random, self-control and yoked). In conclusion, target exclusion was not an effective method for learning and did not support the efficacy of uncertainty-based practice for learning novel skills. There were benefits from keeping easier/low error skills in practice for later retention. These benefits did not appear to be related to the increased switching between skills, but could be related to increased task engagement and more optimal challenge associated with practice on a range of target difficulties, rather than the most difficult.