Śaṅkarācārya Bĥaratī Tīrtha

रूपं दृश्यं लोचनं दृक् तद्दृश्यं दृक्तु मानसं ।
दृश्या धीवृत्तय साक्षी दृगेव न तु दृश्यते ॥
rūpaṁ dṛśyaṁ lōcanaṁ dṛk taddṛśyaṁ dṛktu mānasaṁ
dṛśyā dhīvṛttaya sākṣī dṛgeva na tu dṛśyate

"Form is seen and the eye is the seer; it [the eye] is seen whereas the seer is the mind; the seen are the the modifications (vṛttis) of the mind, whereas the Witness (the Self) is verily the seer, but It (the Self) is never seen (by any other)."

Dṛgdṛśyavivēkaḥ, Discrimination (viveka) between the seer (Dṛg) and the seen (dṛśya)