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Motor performance is classically described as improving nonlinearly with practice, demonstrating rapid improvements early in practice with stabilization later, which is commonly modeled by exponential decay functions. However, retrospective analyses of our previously collected data challenge this theoretical model of motor skill acquisition, suggesting that a majority of individual learners actually demonstrate patterns of motor improvement different from this classical model. A convenience sample of young adults, older adults, and people with Parkinson disease trained on the same functional upper-extremity task. When fitting three-parameter exponential decay functions to individual participant data, the authors found that only 13.3% of young adults, 40.9% of older adults, and 66.7% of adults with Parkinson disease demonstrated this "classical" skill acquisition pattern. Thus, the three-parameter exponential decay pattern may not well-represent individuals' skill acquisition of complex motor tasks; instead, more individualized analysis methods may be warranted for advancing a theoretical understanding of motor skill acquisition. [ABSTRACT FROM AUTHOR]

Deficits in sequence-specific learning (SSL) may be a product of Parkinson's disease (PD) but this deficit could also be related to dopamine replacement. The purpose of this study was to determine whether dopamine replacement affected acquisition and retention of a standing Continuous Tracking Task in individuals with PD. SSL (difference between random/repeated Root Mean Square Error across trials) was calculated over 2 days of practice and 1 day of retention for 4 groups; 10 healthy young (HY), 10 healthy elders, 10 individuals with PD on, 9 individuals with PD off their usual dosage of dopamine replacement. Improvements in acquisition were observed for all groups; however, only the HY demonstrated retention. Therefore, age appeared to have the largest effect on SSL with no significant effect of medication. Additional research is needed to understand the influence of factors such as practice amount, task difficulty, and dopamine replacement status on SSL deficits during postural tasks. [ABSTRACT FROM AUTHOR]

This study investigated whether grip type and/or task goal influenced reaching and grasping performance in poststroke hemiparesis. Sixteen adults with poststroke hemiparesis and twelve healthy adults reached to and grasped a cylindrical object using one of two grip types (3-finger or palmar) to achieve one of two task goals (hold or lift). Performance of the stroke group was characteristic of hemiparetic limb movement during reach-to-grasp, with more curved handpaths and slower velocities compared with the control group. These effects were present regardless of grip type or task goal. Other measures of reaching (reach time and reach velocity at object contact) and grasping (peak thumb-index finger aperture during the reach and peak grip force during the grasp) were differentially affected by grip type, task goal, or both, despite the presence of hemiparesis, providing new evidence that changes in motor patterns after stroke may occur to compensate for stroke-related motor impairment. [ABSTRACT FROM AUTHOR]