Abstract:

Aim: The aim of this study was to test Obsessive Compulsive Disorder (OCD) is associated with a dysfunctional motor system that cannot appropriately form a forward model of the completed state of an action.   Material and Methods: In three computerized experiments, reaction times to verbs denoting different aspects constituted the main dependent variable. They were conducted to test the hypothesis that patients with OCD would have difficulties in sentences with perfective aspect and/or completed actions and, hence, display longer reaction times to associated stimuli. 40 participants with OCD and 40 non-obsessive controls were included in the study. Experiment 1 was a visual lexical decision task in which participants were instructed to decide on the word/non-word status and, simultaneously, on the temporal reference encoded by stimuli presented on the screen. In Experiment 2, participants had to carry out a number of actions and to rate stimulus sentences that represented either accurate or inaccurate descriptions of the completeness of the actions they themselves carried out. In Experiment 3, participants rated the truth-values of stimulus sentences in relation to the tasks that they had previously carried out in Experiment 2.   Results: Patients with OCD displayed significantly longer reaction times to sentences with actions in the perfective aspect.   Conclusion: The results obtained may be taken as support for the assumption that the feedforward motor control of actions in OCD is problematic.

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