Hallucinations are a common symptom of schizophrenia. Some clients experience auditory and visual hallucinations (AVH), while others experience olfactory hallucinations (OH). Although both types of imagined experiences can be frightening and disturbing, OHs are particularly unpleasant because clients who have OHs often report smelling very bad smells that cause them to be quite distracted and agitated. Understanding the processes that cause AVH and OH and why some clients exhibit both types of symptoms while others only exhibit one were the focus of a recent study led by Deborah Arguedas of the ARC Center of Excellence in Cognition and Its Disorders at Macquarie University. Arguedas examined source monitoring and the ability to determine the source, either real or imagined, of stimuli in an experiment conducted with 26 schizophrenic clients with either AVH, OH, or both and 27 control participants.
After a series of experiments in which the participants were exposed to several different scents, Arguedas found that the recall of the frequency of the scents was significantly skewed in the clients with OH. Specifically, the clients with OH believed they had smelled the scents many more times than they actually had. Additionally, they were particularly sensitive to the bad odors and reported excessive numbers of exposure during recall, which far exceeded the actual number of times the scent was administered. The AVH clients also experienced increases in imagined frequency, but not as severely as those with OH. Both groups however, had many more imagined scent exposures than the control group did during the recall portion of the experiment.
Arguedas believes the results of this study demonstrate a clear presence of impaired source monitoring abilities in the participants with schizophrenia. During the auditory task, the AVH clients showed higher levels of imagined recall than the OH clients; however, the levels were not as high as those in the previous task. Therefore, the study implies more significant impairment in the source recognition abilities of individuals with schizophrenia and OHs than in those with AVHs alone.
Arguedas, D., Stevenson, R. J., Langdon, R. (2012). Source monitoring and olfactory hallucinations in schizophrenia. Journal of Abnormal Psychology. Advance online publication. doi: 10.1037/a0027174
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