Yōga Sūtra 2.06

दृग्दर्शनशक्त्योरेकात्मतेवास्मिता।

Ego (asmita) unites the act of observing, the perceived seen, and the person observing - as if one single self.

It is ego which unites all activities of senses, mind, and the experiences so generated to give the impression of one single self.