Investigating Cognitive Inhibition in Dissociative Identity Disorder Compared to Depression, Posttraumatic Stress Disorder and Psychosis

Cognitive inhibition refers to the mental capacity to suppress distracting stimuli that compete with target stimuli for processing resources. Using neutral word stimuli in a flanker task, a recent study suggested that dissociative identity disorder (DID) is characterized by weakened cognitive inhibitory functioning (Dorahy, Irwin, & Middleton, 2002). The current study used single digit stimuli in the flanker task and tested cognitive inhibitory ability in samples with DID, depression, posttraumatic stress disorder and psychosis. The DID, depressed and PTSD groups displayed no evidence of weakened cognitive inhibitory functioning. Consistent with previous research, however, the psychosis sample displayed a reduced capacity to engage in cognitive inhibition. Cognitive inhibitory ability was not related to measures of dissociation, childhood traumatic experience or schizotypy. Results are discussed in terms of the positive symptoms of schizophrenia and the nature of stimuli used in the flanker task.