I would argue that you're confusing "brain receiving complete information" with "brain doing inference on what information it does receive to get you close enough". You don't need the full screen to tell that the image is SD vs HD, you just need to glance at a small segment. That's not 100s of mb/sec. You know that the rest of the video is happening in your peripheral, and maybe you can tell what's going on. But in actuality you're receiving a very low bit rate version of that, and your brain is simply telling you "X & Y are happening in HD in your peripheral" and it's convincing enough.