SCALING OF MOVEMENT VELOCITY - A MEASURE OF NEUROMOTOR RETARDATION ININDIVIDUALS WITH PSYCHOPATHOLOGY

The study of motor slowness based on observational methods has limitat ions. Whether motor retardation has a psychomotor or neuromotor basis is unclear because psychiatric and motor symptoms overlap. Observation al methods lack the precision necessary to distinguish cognitive from motor processes. For the present study, we used an objective measure o f neuromotor dysfunction to quantify the extent to which an individual programs movement velocity in anticipation of increasing target dista nce. Persons with Parkinson's disease (PD) or functional psychosis wer e studied with a group of healthy comparison subjects. Results indicat ed that the slope of the linear function relating velocity to distance was abnormal in the PD group and in approximately half of the psychos is group. Analyses revealed the measure to have high specificity and s ensitivity. Weak correlations between velocity scaling and psychopatho logy support the neuromotor basis of the measure. We conclude that thi s measure of velocity scaling is relatively uninfluenced by cognitive factors that may underlie psychomotor retardation.