Effects of delayed visual feedback on handwriting in Parkinson's disease

Parkinson's disease (PD) affects fine motor control, and handwriting may be particularly affected. Several researchers have postulated that PD patients become overly dependent on visual feedback, although prior results have been inconsistent. Discrepancies may be due to the presence or absence of a spatial target, and to medication effects. In the present study, we compared five nondemented PD subjects with five age-matched controls on a handwriting task performed with and without guidelines. Visual feedback was either normal or delayed, to assess dependency on visual information. Effects of medication were assessed by testing PD subjects in undermedicated and well-medicated states. Of the five PD subjects, two wrote in a manner similar to controls across all conditions, two consistently used a non-ballistic mode of writing, and one was micrographic. All PD subjects except the micrographic subject modified their handwriting in response to delayed feedback in a manner similar to controls. Medication affected PD subjects differently, producing an increase in size for the micrographic subject, and an increase in acceleration in the two PD subjects with normal writing. Comparisons of group effects with individual profiles illustrate the importance of recognizing individual differences within PD samples.