Neurobiological bases of interval timing : Effects of Parkinson's disease
Degree GrantorUniversity of Canterbury
Degree NameMaster of Arts
Temporal information processing in people with parkinson's disease [off medication] and in healthy controls was investigated using a psychophysical choice procedure and an interval production task in two time ranges, milliseconds and seconds. There were no differences between groups on a frequency bisection task [control task, non-timing]. Control subjects produced equivalent Weber fractions in the estimation [bisection] task for the milliseconds range [200 ms 800 ms] and in the seconds range [1-4 seconds]. The PD group showed poorer performance only in the millisecond estimation task. For the interval production task, the parkinsonian subjects produced higher coefficient of variation values for total variance irrespective of range tested [target inter-tap intervals of 550ms and 2.25s]. The use of verbal suppression/no-suppression had little or no influence on these findings. Separate clock and motor-delay variance was estimated using the Wing and Kristofferson  model. Analysis of the subset of subjects whose data did not violate the model's assumptions produced a group difference on this task but indicated that both clock and motor deficits, irrespective of range would be found if larger sample sizes are used. Coefficients of variation were higher in the seconds tapping task for both the PD and the control subjects. These findings suggest that parkinsonian individuals when tested off medication do not exhibit the scalar property, that is a constant source of variability across time. The effects of Parkinson's disease on timing performance appears to be task-dependent.