Date of Award


Document Type


Degree Name

Doctor of Psychology (PsyD)



First Advisor

David J. LaPorte, Ph.D.

Second Advisor

Dasen Luo, Ph.D.

Third Advisor

William M. Meil, Ph.D.

Fourth Advisor

Michael D. Franzen, Ph.D.


Intraindividual variability refers to short-term fluctuations in performance that may be indexed as trial-to-trial variability on response time (RT) tasks. A growing body of evidence suggests that such variability may be a sensitive indicator of the integrity of prefrontal cortical regions. This possibility was tested in a broad clinical sample by investigating the relationship between intraindividual variability on the Wisconsin Card Sorting Test and a large battery of executive functioning tasks using mathematical models of RT variability. The executive functioning tasks predicted intraindividual variability with a large effect size. The relationship between intraindividual variability and cognitive control tasks was marginally higher than the intercorrelations of the tasks themselves. Thus, intraindividual variability demonstrates considerable convergent validity with more traditional neuropsychological assessment techniques. Trial-to-trial variability was specifically related to measures of set shifting and this relationship was only partially mediated by more basic attentional functions. The findings of this study are consistent with the interpretation that intraindividual variability in response time may index the consistency with which individuals are able to regulate various cognitive control subprocesses involving attentional control, active engagement of response sets, and the ability to suppress task irrelevant information in the pursuit of a self-selected goal. The primary neurostructural substrates of RT variability may lie within prefrontal cortical regions including ventrolateral, dorsolateral, and anterior cingulate cortex. Future research may set the stage for a new clinical measurement tradition based on the application of intraindividual variability data.