Electronic Thesis and Dissertation Repository


Master of Science


Health and Rehabilitation Sciences


Dr. Andrew Johnson

2nd Supervisor

Dr. Jeff Holmes

Joint Supervisor


Performing two tasks simultaneously is ubiquitous in everyday life, and the resulting interference may degrade performance on one or both of the tasks. This is potentially important, as diminished performance of a postural task places an individual at a greater risk for falling, especially in a movement impaired population such as individuals with Parkinson’s disease (PD). Many secondary tasks have been shown to reduce the performance of gait and balance, but to date only one study has investigated the effects of a verbal secondary task that systematically controls articulatory, cognitive, and linguistic demands. Previous research suggested that these components have independent effects on gait and balance within a sample of healthy young adults. The purpose of the present study was to replicate this previous research, within a sample of healthy older adults (n=20) and a sample of individuals with PD (n=20), and to evaluate the effects of individual differences in information processing speed, on dual-task interference. Results suggested that oral-motor movement significantly affected parameters of gait and balance, with men displaying significantly more dual-task interference than women. The addition of speech and lexicality to the secondary task did not significantly increase interference during the gait or balance protocol. Results also indicated that dual-task interference is directly related to individual differences in information processing speed, a finding that supports the capacity-sharing model of dual task interference.