An event-related potentials investigation of semantic access during thought suppression
The paradoxical effects of thought suppression were first demonstrated in an experiment that found that thoughts of a white bear were more likely to recur for people who initially suppressed thoughts of a white bear than for people who initially expressed such thoughts (Wegner, Schneider, Carter, & White, 1987). Recent findings suggest that this rebound effect is due to the simultaneous facilitation of associative pathways leading towards and away from the suppressed thought (Najmi & Wegner, 2008). The following study used event-related potentials (ERPs) to investigate the semantic activation of individual words during thought suppression. Participants were asked to suppress or express thoughts of a focus word during a simple lexical decision task (LDT), while brain responses were measured, time-locked to focus and distracter words. Modulations in the N400 component, an index of word activation, demonstrated an ironic increase in focus word activation during and after suppression periods relative to expression, although earlier differences in the N1 window suggest that expression elicited greater perceptual processing than suppression. A P300 effect was also observed which was larger for focus words than distracter or non-words, implying that focus words were treated as targets in the LDT, although non-words were the only stimuli requiring a manual response. Overall, results demonstrate the paradoxical effects of thought suppression occurring at the level of semantic access.