Title

Effects Of Rhythmic Context on Time Perception in Individuals with Parkinson Disease

Date of Award

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Psychology/Experimental

First Advisor

John McAuley, D. (Committee Chair)

Second Advisor

Dale Klopfer (Committee Member)

Third Advisor

Sheryl Coombs (Committee Member)

Fourth Advisor

Alexander Goberman (Committee Member)

Abstract

Parkinson disease (PD) is a neurodegenerative disorder of the basal ganglia (BG) that results in a significant loss of dopaminergic neurons. Previous studies have shown that individuals with PD show impairments in both the perception and production of duration, supporting the involvement of the BG and dopamine (DA) in perceptual and motor timing. One such DA-dependent timing impairment is gravitation in the remembered duration of an isolated (single) time interval toward the mean of a set of experienced time intervals (Malapani, et al., 1998). This dissertation extends research on time perception in PD to an investigation of the effects of rhythmic context on perceived duration. The basis for the project is a paradigm previously shown to produce large effects of rhythmic context on perceived duration in young adults (Barnes & Jones, 2000; McAuley & Jones, 2003). In this paradigm, participants are asked to compare the duration of two empty time intervals marked by pairs of tones (a fixed standard interval followed by a variable comparison interval) with the instruction to ignore a preceding tone sequence (i.e., context rhythm). Previous studies have shown that participants are unable to ignore the context rhythm, as evident by relative duration judgments about the standard-comparison pair of intervals being more accurate when the tone marking the end of the standard interval is ‘on time,’ relative to a periodic extrapolation of the context rhythm, than when the tone marking the end of the standard interval is ‘early’ or ‘late.’ The resulting ∩-shaped pattern of performance has been termed a temporal expectancy profile. Two experiments tested two hypotheses about the strength of the expectancy profiles in young adults, older adults, and individuals with PD. The first hypothesis is a period-correction hypothesis that posits that increasing the number of repetitions of the standard interval will eliminate (or at least weaken) the expectancy profile. The second hypothesis is a DA-mediated distortion hypothesis that posits that larger effects of rhythmic context will be observed when individuals with PD are tested off their DA-enhancing medication than when tested on medication. Moreover, the loss of DA in individuals with PD will result in larger effects of rhythmic context than observed with older adult controls or young adults. Experiment 1 tested young adults in order to provide a baseline measure of performance and to provide an initial evaluation of the period-correction hypothesis, whereby effects of rhythmic context on perceived duration were predicted to be eliminated (or at least weakened) by increasing the number of repetitions of the standard interval. Experiment 2 compared the performance of individuals with PD (both on- and off-medication) to older adult controls and to the young adults tested in Experiment 1. In general, support for the period-correction hypothesis was found. Increasing the number of equal standard intervals reduced the effects of rhythmic context on perceived duration in all groups. Mixed support was found for the DA-mediated distortion hypothesis. Although no group differences were observed in the strength of expectancy profiles for the one-standard interval condition, increasing the number of equal standard intervals differentially affected individuals with PD on- and off-medication. Increasing the number of equal standard intervals served to weaken expectancy profiles for PD participants when they were on medication, but not when the same participants were off their medication. Taken together, the present findings provide the first evidence for the potential involvement of DA in period-correction processes.