| This dissertation was designed to investigate the neural basis implementing the contextual interference effect in motor skill learning. Sixty-one non-disabled adults were recruited. Participants practiced three fast, discrete, goal-directed arm movements each with specific time and amplitude requirements. The motor tasks were practiced either in a blocked or quasi-random order. Transcranial magnetic stimulation (TMS) was applied to the arm areas of the cortical motor system (CM) to directly perturb brain processing during motor practice. Single TMS pulses were delivered, synchronized to each inter-trial interval. The three stimulation conditions (no TMS Control, TMS, Sham) and two practice orders (Blocked, Random) factorial design resulted in six experimental groups. Testing took place over 2 consecutive days with acquisition and immediate retention phases on day 1 and a delayed retention phase on day 2. The retention tests consisted of trials without feedback with which neither TMS nor Sham-TMS applied.;This dissertation is organized around a single experiment designed to answer three separate, yet related research questions (Chapters 2, 3, and 4). Each will be presented separately with its own unique purpose, methods, results and discussion. Overall, results from this dissertation provide relevant information about the neuromotor and psychological explanations for the CI effect in motor learning. We demonstrated that cortical processing, specifically that involving the arm area of the cortical motor system, is a putative neural locus for the CI effect. In addition to supporting previous findings that human motor cortex contributes to motor skill learning, these results suggest that the level of CM engagement can be modulated by task practice order. With this experimental design, we also tested the two strongest information processing explanations for the CI effect. These findings have important implications for understanding the nature by which fast discrete goal-directed arm movements are best learned. Our work also provides new insights into a beginning foundation for the translation of motor learning principles into advanced and developing therapeutic approaches in neurorehabilitation. |
