Performance of alternating motion rate (AMR) in individuals with Parkinson's Disease under external and internal cueing conditions

Consistent, considerable rate deficits in individuals with Parkinson's Disease (PD) have long since been established. The intention of this study was twofold: (1) to add to the body of existing research regarding the rate pattern of individuals with PD on AMR specific tasks, and (2) to investigate the effects of external auditory cueing on rate performance. Further research in the area of rate deficits and external cueing in PD is needed in order to guide future clinical directions regarding efficacious rate treatment methods. To assess AMR performance of individuals with PD under both the presence and absence of an external cue, acoustic analysis of sound waveforms of 11 healthy control subjects and 16 subjects with PD was conducted. Each subject performed AMR tasks under 3 conditions: an internal condition in which no external auditory cue was provided, an external condition involving presentation of a 4 Hz auditory cue, and a second external condition involving presentation of a 6 Hz auditory cue. As a group, subjects with PD generated a slower internal rate than healthy controls. When external cues were provided, AMR rates of subjects with PD more closely matched those of the healthy controls, and individual examination revealed that the majority of subjects both with and without PD were able to manipulate their rate to closely match the external cue. Cue presence did not seem to assist subjects with PD in sustaining evenness of rate. This study further points to the inconsistencies in rate aberrancies in the PD population. Not only was there unequivocal rate variation within the PD subject group as a whole, but individuals with PD also demonstrated considerable intrasubject variances within and across conditions. In conclusion, close examination of the individual with neurological compromise secondary to PD is critical for developing clinical conclusions regarding most efficacious speech therapy methods to target rate aberrant motor-speech characteristics, as heterogeneity within the PD population can prevent inclusive and valid group-based conclusions. This is by no means a novel outcome but rather further corroborates prior studies.