What Flips Attention?

A central feature of our waking mental experience is that our attention naturally toggles back and forth between "external" and "internal" stimuli. In the midst of an externally demanding task, attention can involuntarily shift internally with no clear reason how or why thoughts momentarily shifted inward. In the case of external attention, we are typically exploring and encoding aspects of our external world, whereas internal attention often involves searching for and retrieving potentially relevant information from our memory networks. Cognitive science has traditionally focused on understanding forms of internal and external attention separately, leaving a mystery about what sparks the seemingly automatic shifts between the two. Specifically, what shifts attentional focus from being outward-directed to being inward-directed? We present a candidate mechanism: Familiarity-detection.