How paradoxical are the effects of thought suppression? : the nature of mental control and the factors that influence it
This thesis attempted to expand knowledge of intentional thought control in several directions. The primary aim was to provide an account of intentional thought suppression by relating the phenomenon to the methods used to assess the rebound effect, internal personality factors and psychopathology. An additional aim was to examine the rebound effect from the broader perspective of relating thought suppression to aging, the perception of volitional control and memory for future intentions. The results indicate that the method used to index the rebound effect may have a large impact on whether the effect is found or not. The rebound effect was obtained with the original method of assessment (Wegner, 1987) but not with the modified method that is currently used in the research. More importantly, the rebound effect was affected by the personality variable of state vs. action orientation (Kuhl & Beckmann, 1994b). State oriented participants demonstrated the rebound effect, whereas action oriented participants did not, irrespective of the method used to assess the effect. This finding provides support for the new intentional account of the rebound effect proposed in the thesis that is based on the Intention Superiority Effect (Kuhl, 1994) and the theory of action control (Kuhl & Beckmann, 1994b). The results also showed that suppression and expression performance in the laboratory did not have a common underlying mechanism. Successful expression performance was related to poorer suppression performance and visa versa. The results of the thesis also question the validity of the White Bear Suppression Inventory (Wegner and Zanakos, 1994)a s a measure of the tendency to suppress thoughts in everyday life. In young adults, apart from thought suppression, it also appears to measure the tendency to experience thought intrusions (rumination). Moreover, there was no relationship between the use of thought suppression in everyday life and actual suppression performance in the laboratory. A different pattern of results were obtained in a group of older adults (over 65 years). In addition, older adults reported using thought suppression reliably less frequently than young adults (i. e. had lower WBSI scores), and displayed much higher levels of repressive coping style than young people, 37% (old) vs. 9.5% (young). Finally, the results showed that thought suppression can also have other ironic effects on behaviour and perception. Participants attempting to complete an action while suppressing thoughts of the intention to perform this action came to feel as if the act was less intentionally performed. In contrast, participants completing actions under thought expression instructions rated the actions as more intentional. Furthermore, suppressing or expressing thoughts of an upcoming intention did not help one to remember to enact the intention with an enhanced frequency relative to thinking about a completely unrelated intention. Taken together, the findings have important implications for research on thought suppression and mental control by showing that the rebound effect is less robust than suggested by previous research. Thus, some of the controversy surrounding the rebound effect can be explained on the basis of individual differences in personality type (state vs. action orientation) as well as the methods used to index the effect. The results also raise several important questions for future research in this area (e. g. the validity of WBSI, effects of age on thought suppression and repression).