Subject characteristics and performance on cognitive tasks.

Values reported are sums, mean (SD), or median (range). Abbreviations: BTA = Brief Test of Attention; HC = healthy control; MMSE = Mini-Mental State Examination; MSAp = parkinsonian variant of multiple system atrophy; MVC = maximum voluntary contraction; ns = not significant; PD = Parkinson’s disease; PSP = progressive supranuclear palsy; UPDRS = Unified Parkinson’s Disease Rating Scale.