Why the mind wanders: How spontaneous thought's default variability may support episodic efficiency and semantic optimization

This chapter offers a functional account of why the mind- when free from the demands of a task or the constraints of heightened emotions- tends to wander from one topic to another, in a ceaseless and seemingly random fashion. We propose the default variability hypothesis, which builds on William James's phenomenological account of thought as a form of mental locomotion, as well as on recent advances in cognitive neuroscience and computational modeling. Specifically, the default variability hypothesis proposes that the default mode of mental content production yields the frequent arising of new mental states that have heightened variability of content over time. This heightened variability in the default mode of mental content production may be an adaptive mechanism that (1) enhances episodic memory efficiency through de- correlating individual episodic memories from one another via temporally spaced reactivations, and (2) facilitates semantic knowledge optimization by providing optimal conditions for interleaved learning.