Department of Psychology


There has been a disproportionate level of attention invested on inhibitory deficits in OCD to the reciprocal neglect of facilitation processes. This thesis makes an important contribution to the OCD literature by examining changes in both facilitation and inhibition across several tasks by systematically manipulating stimulus repetition sequences and by charting the temporal courses of these processes by varying interstimulus intervals (ISIs).

Study 1 comprised 3 sequential experiments and was designed to overcome limitations of commonly used tasks. Priming and Go/Nogo tasks were modified and trialed at multiple ISIs from 600-1000ms to examine the temporal course of facilitation and inhibition in normal controls. The results supported the use of two paradigms that were employed in Study 2.

Study 2 comprised a systematic examination of facilitation and inhibition abnormalities in OCD. Three groups, OCD (𝑛 = 21), normal control (𝑛 = 21), and GAD participants (𝑛 = 18) completed the modified priming task at 1000ms ISI and the modified Go/Nogo task at two ISIs (600ms and 1000ms). OCD participants exhibited enhanced facilitation compared to anxious and normal control groups on both tasks, indicating that facilitation abnormalities in OCD was a reliable and robust finding and that these effects may be specific to OCD. Further, group differences were best detected at earlier ISIs (600ms), and early in the repetition sequence. The thesis findings contribute to a better understanding of the mechanisms that may underpin clinical symptoms in OCD and have important theoretical and treatment implications. A second valuable contribution of the thesis to both experimental and clinical research is the validation of a new and effective paradigm that can chart facilitation effects across stimulus repetitions and temporal variations.