Aitareya Aranyaka (II.iii.2.5) of the Rig Veda tells us that in man alone is the Atman ('Self') most manifest, for man is best endowed with intelligence and discrimination, and who knowing the higher and the lower worlds aspires to achieve immortality through mental things.
Vichara, Self-inquiry, also called jnana-vichara or by devotees of Ramana Maharshi, is the constant attention to the inner awareness of 'I' or 'I am'.