Dissertation Date: March 17, 2025
Sensorimotor adaptation is a form of motor learning whereby a motor skill is adjusted in
the face of a disturbance to return performance to desired performance. This process employs the use of memories to maintain previous experiences to guide future movements. While the
temporal characteristics of adaptation have been well studied, it is not clear as to whether these
memories are explicit, implicit, or a mixture of both. In this Dissertation, I conduct three studies
to investigate the relative contributions of sensorimotor memories when adapting to stochastic
spring-like loads applied to the hand. By implementing computational modeling and system
identification techniques, I fit memory models to movement errors and external disturbances to
yield the relative contributions of sensorimotor memories. In Aim 1, I determined if the
memories used in sensorimotor adaptation to stochastic loads were predominantly explicit or
implicit. Participants grasped a handle of the robotic device and performed out-and-back reaches
while the robot imposed spring-like forces to oppose movement. Immediately after each reach,
participants reported where they thought they moved an assay of explicit memory of
performance. Model fits revealed that explicit memories of performance did not outperform
models that only contained actual reach error a proxy of implicit memory. Thus, sensorimotor
adaptation predominantly used implicit memories. In Aim 2, I determined if these implicit
memories were susceptible to change if participants explicitly attempted to underperform during
the reaching test. Participants were instructed to simulate having a concussion (moving slower,
less accurate, and having memory deficits). The relative contributions of sensorimotor memories
did not significantly change when subjects attempted to sabotage the test, further supporting the
notion of inaccessible implicit mechanisms at play. In Aim 3, recently concussed individuals
participated in a longitudinal study wherein I observed changes in the relative contributions of
motor memories as their injury recovered. Concussion did impact the process of sensorimotor
adaptation, but practice effects obscured initial effects of the injury on sensorimotor memories.
This work provides novel insights into how explicit and implicit processes interact during motor
learning and adaptation, offering potential applications for assessing motor control after brain
injury.
