Fifteen older adults (M = 68 years old) and 15 young adults (M = 23 years old) participated in a speed–accuracy task in which aiming movements were performed on a digitizing tablet to assess movement slowing and variability in older adults. Target-size and movement amplitude influences were analyzed separately to determine if they affected the performance of the young and older adults differently. When target size was increased, older adults did not increase the relative distance traveled in the primary submovement. When movement amplitude was increased, older adults did not scale movement velocities to the same magnitude as young adults did. Both the inability to scale velocity and the inability to increase the relative distance traveled in the primary submovement contribute to slower, more variable movements observed in older adults depending on task parameters. Thus, these data reveal that manipulation of target size and movement amplitude yield two distinct factors that contribute to slowness of movement in older adults.

Objectives:Previous research suggested that people with Parkinson’s disease are able to increase handwriting stroke size up to 1.5 cm without an increase of stroke duration; whereas age matched individuals in normal health are able to modulate stroke size without changes in stroke duration for sizes up to 2 cm. This study was designed to test this finding by examining whether sizes larger than 1.5 cm show different relationships with stroke duration for patients with Parkinson’s disease as compared with age matched controls. Methods:The study included 13 subjects with Parkinson’s disease and 13 age matched controls. Participants were required to write a cursive “llllllll” pattern, or a cursive “lililili” pattern without the dots, at a comfortable speed and also as fast as possible, in five different sizes (1.0, 1.5, 2.0, 3.0, and 5.0 cm). The participants wrote with a ballpoint pen on a digitiser tablet. The target pattern was displayed at its required size on a screen, but disappeared as soon as the pen touched the surface of the digitiser tablet. Online visual monitoring of the hand was prevented by a cover over the digitiser. After each trial, the recorded movement of the tip of the pen was displayed with two lines to indicate whether the size requirement had been met. The writing conditions were presented in random order and consisted of 12 trials for each participant. Results:The results demonstrated that stroke size and duration produced by the participants with Parkinson’s disease were independently modulated up to 1.5 cm; sizes over 1.5 cm resulted in progressive undershooting by patients with Parkinson’s disease (PD). It was also shown that these participants modulated acceleration measures inefficiently as compared with controls. Conclusions:The findings suggest that individuals with Parkinson’s disease writing at speed produce inadequate stroke sizes when these should equal or exceed 1.5 cm.