Investigating the appraisal structure of spontaneous thoughts: evidence for differences among unexpected thought, involuntary autobiographical memories, and ruminative thought

Involuntary thinking occurs when mental states arise without intention. Such thoughts can take different forms, such as involuntary autobiographical memories (IAM), ruminative thoughts, and unexpected thoughts—all of which are popular areas of study, albeit in somewhat disparate literatures. Despite these mental states sharing a common thread of feeling involuntary in nature, it is nevertheless unclear what separates them phenomenologically. We conducted a set of exploratory and confirmatory experiments to elucidate the appraisal dimensions behind these forms of involuntary thought, with a particular interest in understanding the phenomenology behind unexpected thoughts that are predicted to violate expectations of both timing and content. Across two experiments, we found that unexpected thoughts had unique appraisal structures compared to the other two forms of involuntary thought: they were less identifiably cued, more surprising in content and timing, and offered new information (i.e., insight). We discuss how these distinctions support recent theories regarding the nature of unexpected thought and its relation to other forms of involuntary thinking, namely IAM and ruminative thought, which are the more commonly studied forms of involuntary thinking. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00426-023-01814-y.