Generally, the suppression of unwanted thoughts is found to be ineffective. Moreover, in the longer run, suppression attempts may backfire in that they produce a delayed increase in unwanted thoughts (i.e. a rebound effect). This ineffectiveness and paradox have been observed in various studies, and with various targets, such as neutral thoughts, obsessive intrusions, worries, addictive urges, and phobia-related cognitions. The present study sought to explore the effect of suppression of a different intrusion, namely a hallucination. Healthy undergraduates were exposed to a laboratory procedure that was to provoke hallucinations. Half of the participants were additionally given instructions to suppress the hallucinations. Results indicated that suppression was somewhat effective in the short run, but ineffective in the long run. However, no rebound effect was observed.
