| Dysfunctional cognitive control plays a central role in the occurrence and maintenance of rumination and depressed mood. For a better understanding of the cognitive, psychophysiological, and emotional characteristics involved in cognitive control in depression, this dissertation consists of three studies that investigate the forgetting of self-generated, emotional material in individuals diagnosed with major depressive disorder (MDD) as compared with healthy controls (HCs). In the first study, the relationship between self-complexity and retrieval induced forgetting (RIF) was assessed in order to examine the underlying mechanisms and individual differences in forgetting unwanted thoughts. As a result, individuals with MDD demonstrated reduced recall of unpracticed but competing negative words (e.g. RIF effect), especially as they came up with more categories relevant to aspects of themselves or their life with less overlap among them. In the second study, event-related potentials (ERPs) in response to valenced self-relevant information in a directed forgetting (DF) task were obtained to examine if either attentional inhibition or lack of elaborative processing or both were related to intentional forgetting, and if those cognitive processes underlying DF varied by valence. The results suggested that HC individuals initiated effortful allocation of attentional resource to remember non-mood congruent (negative) material in early stage of information processing (indexed by the P300 ERP component). HC individuals also demonstrated preferential elaboration and rehearsal of positive self-relevant information in remembering compared to negative one (e.g. positive bias; indexed by the slow wave component). In contrast, individuals with MDD showed even-handed processing of positive and negative stimuli, and also passive and less effortful processing for both remembering and forgetting. In the third study, Joormann et al.'s (2009) forgetting training was revised to better model naturalistic cognitive behavioral therapy process. Therefore, unlike in previous studies, a Think/No-Think (TNT) task with self-referent material and a pre- and post-task mood measurement was administered. As a result, individuals with MDD showed below-baseline forgetting of negative self-relevant information when provided positive substitutes. However the expected mood change was not observed in the MDD group. Implications and limitations of the studies are discussed and future directions are suggested. |
