This Atman is a self-cognised entity
215. That which is perceived by something else has for its witness the latter. When there is no agent to perceive a thing, we cannot speak of that thing having been perceived at all.
216. This Atman is a self-cognised entity, because It is cognised by Itself. Hence the individual soul is itself and directly the Supreme Brahman, and nothing else.
Swami Madhavananda, Advaita Ashrama, 1921, Vivekacudamani: v. 215-216