Communication Disorders Ph.D. Dissertations


The Psychological Refractory Period in Parkinson Disease (PD): Effects of Response Modality and Cognitive Complexity

Date of Award


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Communication Disorders

First Advisor

Alexander Goberman (Advisor)

Second Advisor

Ronald Scherer (Committee Member)

Third Advisor

Howard Casey Cromwell (Committee Member)

Fourth Advisor

Jason Whitfield (Committee Member)

Fifth Advisor

Andrea Cripps (Committee Member)


In addition to motor deficits, it is widely accepted that individuals with Parkinson Disease (PD) experience impairments in cognitive functions including central processing (e.g., Wichmann & DeLong, 2013). Previous research has found that the psychological refractory period (PRP) paradigm is a useful method to examine response time delays attributed to limitations in central processing capacity (e.g., Pashler, 1990). This paradigm allows for the study of an individual’s ability to perform two tasks as they increasingly overlap in time. The current study used the psychological refractory period paradigm to examine the effects of cognitive complexity and response modality in two overlapping tasks in 8 individuals with PD compared to 11 individuals without PD. Specifically, the study aimed to determine how the central process of decision-making affects response times in three different experimental conditions with increasing cognitive complexity (no choice, choice, and overlapping choice conditions) and how vocal versus manual responses are affected by these conditions. Results revealed no significant group (PD vs. Controls) differences for simple reaction or 2-choice response time. Additionally, task overlap did not affect groups differently. A significant task by group interaction was found with participants with PD having significantly longer response times compared to controls only in the more complex task with 3 response options. Overall, results revealed significantly longer response times in PD only in the more complex task but no difference in how task overlap affected groups. These results suggest that delays in response time in PD are related to more central decision or response selection processes in response tasks and not to motor execution. Furthermore, results suggest that there is no slowing of central processes due to task overlap in PD relative to control participants.