Pupil diameter tracked during motor adaptation in humans

Area of Science:

• Neuroscience
• Motor Control
• Cognitive Psychology

Background:

• Pupil diameter changes reflect internal states like surprise and uncertainty.
• Pupillometry is increasingly used in cognitive learning but less so in motor learning.
• Understanding pupil responses in motor learning can offer non-invasive insights into internal states.

Purpose of the Study:

• To characterize pupil diameter changes during short-term motor adaptation.
• To investigate how different force field conditions (abrupt, gradual, switching) affect pupil responses.
• To explore the relationship between pupil diameter, movement error, uncertainty, and novelty.

Main Methods:

• Measured pupil diameter in 121 participants during a reach adaptation task.
• Implemented abrupt, gradual, and switching force field conditions.
• Analyzed phasic pupil dilation during movement and tonic premovement baseline pupil diameter.

Main Results:

• Sudden errors from force field introduction/reversal caused significant pupil dilation and increased baseline pupil diameter.
• Gradual force field introduction led to reduced pupil responses, suggesting unexpected errors drive these changes.
• Error-induced pupil responses habituated with repeated force field reversals; baseline pupil diameter correlated with knowledge of perturbation and slower reaction/movement times.

Conclusions:

• Tonic baseline pupil diameter reflects perceived environmental uncertainty.
• Phasic pupil dilation during movement indicates surprise from sensory prediction errors.
• Novelty modulates both tonic and phasic pupil responses, offering a new non-verbal assessment of internal states in motor learning.