[1] Tan Tock Seng Hosp, Dept Speech Therapy, Singapore 308433, Singapore
[2] Univ Canterbury, Dept Commun Disorders, Christchurch 1, New Zealand
[3] Van der Veer Inst Parkinsons & Brain Res, Christchurch, New Zealand
[4] Univ Otago, Dept Med, Christchurch, New Zealand
[5] Univ Otago, Dept Resp Med, Christchurch, New Zealand