Spontaneous Thought Dynamics: Identifying the Characteristics and Correlates of Thought Transitions Using the Think-Aloud Method

The human mind continuously generates spontaneous thoughts that move fluidly from one topic to another, yet the organization of these transitions remains poorly understood. Recent accounts propose a “clump-and-jump” structure, in which clusters of semantically related thoughts are punctuated by abrupt shifts in content. Here, we tested whether the stream of spontaneous thought exhibits a hierarchical structure comparable to event segmentation in perception and identified features that accompany boundaries between higher- versus lower-level units. 48 students completed a 5-min Think-Aloud Protocol, producing a continuous verbal report that they subsequently hierarchically segmented into coarse-grained units and nested fine-grained units. Transitions between successive segments were then rated on multiple transition features (e.g., perceived linkage, thematic continuity). Furthermore, we used Natural Language Processing embeddings to quantify the semantic similarity between adjacent segments. Participants also completed self-report questionnaires assessing personality and psychological characteristics. Results showed that participants reliably produced hierarchical segmentations, with more fine-grained than coarse-grained units. Transitions between coarse-grained segments involved more category switching and were characterized by weaker perceived linkage, greater contextual discontinuity, and lower thematic continuity than transitions between fine-grained segments. Semantic similarity was lower for coarse-grained than for fine-grained transitions, supporting the construct validity of participant-defined boundaries. Exploratory analyses further suggested that higher ADHD symptoms and daydreaming frequency were associated with more transitions, whereas mindfulness was associated with fewer. Together, these findings provide evidence that our stream of thought is hierarchically structured, identify convergent phenomenological and semantic markers of transitions, and underscore the relevance of these dynamics to individual differences.