Learning vs. minding: How subjective costs can mask motor learning.

Area of Science:

• Motor control and learning
• Biomechanics
• Human aging

Background:

• Kinematic errors in new movement learning are often attributed to reduced motor learning ability.
• This interpretation assumes a uniform error-canceling strategy across individuals.
• An alternative hypothesis suggests individuals may strategically trade off error reduction for lower movement effort.

Purpose of the Study:

• To investigate whether kinematic errors in older adults reflect reduced motor learning or strategic differences in effort cost.
• To re-evaluate the common assumption that greater kinematic error equates to lesser motor learning.
• To explore age-related differences in motor learning strategies.

Main Methods:

• Utilized optimal control theory to model motor learning in younger and older adults.
• Inferred subjective costs (strategies) and internal model accuracy (learning proportion) from trajectory data.
• Fitted a computational model to experimental data to analyze movement strategies.

Main Results:

• Movement trajectories are determined by a combination of learned dynamics and strategic cost weighting.
• Younger adults learned an estimated 65-90% of novel dynamics; older adults learned 60-85%.
• Older adults exhibited a higher relative cost for effort compared to kinematic error, compensating for potentially similar learning extents.

Conclusions:

• The assumption that greater kinematic error implies less learning is challenged.
• Older adults may prioritize effort minimization, leading to larger kinematic errors despite comparable learning.
• Quantifying motor learning requires considering subjective movement costs alongside kinematic outcomes.