Introduction: Behavioral inhibition deficit is considered probable in compulsive washing symptoms. Go-No Go and stop signal paradigms are the frameworks used for studying behavioral inhibition. As in stop signal paradigm it is necessary for participants to inhibit triggered response, we aimed to investigate behavioral inhibition in clinical compulsive washing in this paradigm. Materials and Methods: The cases of this clinical trial were participated among obsessive-compulsive patients who referred to psychiatrists clinics in Mashhad. Number of 30 cases with washing compulsion and 30 cases without disorder were selected. Beck Depression Inventory - version II, Obsessive Compulsive Inventory- Revised (OCI-R) and Stop it test were fulfilled for all cases in the Psychology Clinic of Ferdowsi University of Mashhad. Data analyzed by MANCOVA and SPSS software version 20. Results: The analysis showed that the effect of group factor (F=4.37, P<0.05). The results of MANCOVA analysis showed that there is a significant difference in Stop-Signal Reaction Time (SSRT) between compulsive washing patients and the control group (F=4.298, P<0.05). There is no difference between the two groups in Stop-Signal Delay (SSD) (F=1.265, P=0.18). Conclusion: Significant differences in stop-signal reaction time between the two groups indicated a deficiency in behavioral inhibition in the compulsive washing group. Inability to inhibit triggered response (behavioral inhibition) in compulsive washing patients is consistent with the symptoms of disorder.

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