The Effects of Delayed and Frequency Shifted Feedback on Speakers with Parkinson's Disease

A Lowit, B Brendel, P Howell

Various techniques, including delayed auditory feedback (DAF), have been evaluated as a way of reducing rate for speakers with Parkinson's Disease (PD). Although DAF does not work for all speakers, some can achieve significant improvements in intelligibility with its use. Also, speakers have been reported to remain more natural under DAF than when they use e.g. a pacing board. The fact that naturalness can be retained under DAF contrasts with findings about stuttered speech, where there is unnatural slowing of rate. A further particularly worrying effect of DAF is a reduction in pitch variation. Monopitch is a frequent symptom of PD and the use of a device which aggravates this problem might not be advisable.

Little is known about the prosodic characteristics of DAF speech in PD other than the changes in speech rate and intelligibility. The first aim of this study was therefore to investigate the effects of DAF on Parkinsonian speech in more detail. In addition, speakers were submitted to a frequency shifted feedback (FSF) condition. FSF is known to produce more natural speech in persons who stutter. There are currently no studies reporting how PD speakers perform under FSF conditions. The second aim of this study was thus to investigate whether FSF speech differed from DAF and no-altered-feedback conditions.

The results of 16 speakers with PD and control subjects will be reported in relation to the measures of intelligibility, articulation rate, pause characteristics, rhythm and F₀ modulation.