The construct of mind wandering has notoriously been characterized as heterogenous which may mean that not all types of mind wandering produce the same pattern of results. One operationalization of mind wandering, task-unrelated thoughts (TUTs), can also itself vary in many dimensions, including the emotional valence of TUTs. The current study summarizes several years of work examining the impact that the emotional valence of TUTs has on different aspects of sustained attention. Participants in several studies reported whether their TUTs were negative, neutral, or positive in emotional valence during a sustained attention-to-response task (SART). The first major focus was a meta-analysis where we examined correlations between each TUT valence and SART performance measures. For the second major focus, we tested how different TUT valences changed over the course of the task. The results suggest that negative TUTs typically show stronger associations with SART performance measures, although all TUT valences have numerically similar correlations. Regarding time-on-task effects, across the studies, there was consistent evidence for a linear increase in negative TUTs across blocks. Evidence for this linear increase was not consistent for neutral and positive TUTs. The results of the current study suggest that the relationships between TUTs and performance, and their likelihood of occurring during a task, are not necessarily the same for every type of TUT. These results highlight the importance of continuing to investigate different types of TUTs and different forms of mind wandering, in general, to better understand how this phenomenon occurs. (PsycInfo Database Record (c) 2024 APA, all rights reserved).