Effect of duration of pitch-shifted feedback on vocal responses in patients with Parkinson's disease

Study of the pitch-shift reflex is useful for the investigation of how audi tory feedback is used in the control of voice fundamental frequency. The pr esent study was an attempt to learn if the basal ganglia are involved in ce ntral mechanisms of the pitch-shift reflex by comparing measures of the ref lex in a group of Parkinson s disease patients with those measures in a gro up of control participants. The effect of varying duration of the pitch-shi ft stimulus (PSS) on the voice fundamental frequency (F0) response in 10 Pa rkinson's disease (PD) patients and 10 age-matched unaffected participants was investigated. Participants were instructed to vocalize into a microphon e while their voice was fed back to them over headphones. This feedback of the vocal signal was shifted in pitch either up or down, with the duration of this shift systematically manipulated at 100 ms, 500 ms, and 1000 ms. Al though the participants were on medication, making interpretation of the re sults problematic with regard to basal ganglia function, it was reasoned th at positive effects could nevertheless suggest basal ganglia involvement in this reflex and motivate further research. Results indicated that both gro ups responded to increased stimulus duration of the pitch-shift stimulus wi th increases in reflex peak time, magnitude, and end times. However, PD pat ients had significantly longer peak times and end times than control partic ipants for stimulus durations of 100 ms. These results suggest that basal g anglia dysfunction may affect mechanisms relating to the execution and term ination of the pitch-shift reflex for brief stimulus durations. The results also support hypotheses of impaired sensory integration of auditory feedba ck in PD patients.