[retrac]

There are many studies that look at communication comprehension and retention for where you can see the speaker's face vs. where you cannot.

The results are unsurprising. Being able to see the speaker's face improves comprehension. People rely so heavily on visual information to decode speech that there's a phenomenon known as the McGurk effect; if you set up an experimental rig so the brain receives visual information suggesting one sound but auditory information suggesting another, the visual information often takes priority over what was heard in decoding the speech.

(As someone hearing impaired, this is, pardon the pun, blindingly obvious to me. Sometimes, whether I can understand the words of a talking head on TV depends entirely on whether I look at them or not. But hearing people rely on lipreading too. From what I've read, usually far more than they're aware.)