| dc.description | The effect of premovement target location information on the planning and execution of visually directed pointing movements was examined for healthy young and elderly adults, and adults with mild or moderate Alzheimer's disease (AD), or Parkinson's disease (PD). A response cuing paradigm, modified from Posner (1980) was used in two experiments. In both experiments, targets were presented in an arc-like fashion above a visual fixation point at which informational cues (arrow) indicated the probable location of the upcoming target (valid - 60%, invalid - 20%, neutral - 20%). Subjects were instructed to maintain their gaze at the fixation point until the actual target position was indicated and then to point quickly and accurately to the target. In one experiment, the target was indicated by a change at the target position (exogenous orientation) and in the other, was indicated by information presented at fixation (endogenous orientation). Finger position in three dimensional space was sampled by two WATSMART cameras at a rate of 200 Hz and stored on a computer for analyses. Data were analyzed using General Linear Models Repeated Measures Multivariate Analysis of Variance. Group and cue validity were independent variables. Reaction time (RT), movement time (MT), peak velocity (PV), percent deceleration, and resultant error were dependent measures. Overall differences among the groups for RT, MT, and PV were noted. Exogenous overt orienting had a RT advantage for all groups compared with endogenous overt orienting. All groups were able to use cued information to facilitate movements. For exogenous overt movements, healthy elderly, mild AD and PD subjects made all necessary changes to a preplanned program (i.e., invalid cue) prior to movement initiation, with magnitude differences being evident between the groups. The young and the moderate AD subjects made some changes prior to initiation but made adjustments during execution as well, with the AD group taking much longer to initiate and complete movements than the young. For the endogenous paradigm, healthy elderly subjects made all necessary changes prior to initiation while the young and the mild AD groups made some changes prior to initiation and further modifications during execution, with the AD group taking much longer. The PD group made no changes prior to initiation but made all necessary modifications during movement execution. The moderate AD group were not able to perform this endogenous task, suggesting a hierarchy of decline with disease progression. The experiments used were able to distinguish subtle differences in the effects of premovement visual cues on manual aiming movements with the healthy aging process and among AD and PD groups. An exploratory examination of the laterality of target position relative to the body midline and of the meridian effect was conducted. | en_US |
