External and Internal Attention Are One Shared Operation, Not Two Separate Faculties

Researchers describe external and internal attention as a single selective operation applied in two directions: outward toward sensory inputs and inward toward self-generated mental contents such as memories and rules. Psychologist Michael Posner's 1980 spotlight model and Desimone and Duncan's 1995 biased competition theory together explain how the brain privileges certain perceptual content over others. Chun, Golomb, and Turk-Browne (2011) extended this framework to internal attention, showing the same selection mechanism governs internally generated content. The key claim is not merely that the two modes resemble each other, but that they draw on a single shared pool of cognitive resources with a common capacity limit. A speculative extension suggests attention can also be directed at the system's own ongoing processing, though the authors caution this remains an open question separate from the core argument.