I was absent-minded; I did not hear. I was absent-minded; I did not see. It is thus evident that a person sees with the mind, hears with the mind. Desire, determination, uncertainty, belief, disbelief, steadiness, unsteadiness, shame, intellect, fear all these are in the mind alone. Therefore, when touched from behind, a person knows by the mind.
Brihadaranyaka Upanishad, I-v-3