Abstract
When attempting to suppress thoughts about a target object, intrusive thoughts about the target object increases: this phenomenon is referred to as the paradoxical effect of thought suppression. This study examines this paradoxical effect with more ecologically-valid procedures than those employed in previous studies. Initially, 51 participants tried to solve the “tumor problem”. Next, in a suppression period, the participants in the “suppression” group were instructed to suppress any thoughts about the “tumor problem”, while the participants in the “no-suppression” group were instructed to think freely about anything that came to mind. Finally, in a subsequent free-think period, all the participants were instructed to think freely. Half the participants were asked to sit quietly facing towards a glass screen, while half performed a monotonous task. During the suppression period and the free-think period, the participants made a mark every time thoughts about the “tumor problem” intruded. In addition, after each period, the participants rated degree of intrusion and difficulty of suppression. The suppression group made more marks, i.e., they experienced more frequent intrusive thoughts, and they reported more intrusion and difficulty of suppression than the no-suppression group. These paradoxical effects were equally evident in both the monotonous-task condition and the no-task condition. Moreover, the suppression effects lasted for about a week. The no-suppression group showed superior incidental memory for the tumor problem. The diversity of intrusive thoughts is discussed based on the introspective reports by the participants.
