There's an interesting video on the fastest meaningful musical tempo or speed, which looks at the interonset interval. It turns out that between 100ms and 50ms seems to be that limit: 10 to 20 beats per second. Or, at the low end, 20 Hz.
Which is the point at which a series of beats becomes a tone.
If you extend this out to a full day, and consider each beat a bit, via GNU Units:
You have: 20 bit/s
You want: M bit /day
* 1.728
/ 0.5787037
Mind, that's individual beats, which isn't how we convey information, but it's an interesting data rate limitation. Language encodes at different levels, and arguably people might be able to operate at higher levels.
For spoken English, most of us can accommodate roughly 100 words/min. A typical college-educated adult can read 300 words/minute, and at the high end, perhaps double that. (The less literate are closer to the 100 words/min of spoken speech.)
If a word is considered as 8 bytes (7 characters and a space), then a sustained maximum-rate reading pace would allow for just shy 7 MB per day of information consumed.
Speaking? About 1.1 MB/day.
Both of those assume a full 24 hour day without break, interruption, or sleep.
We can absorb more information in the form of complex tonal or visual signals, but I'd argue that the retention of that information is highly limited.
Any information that a human processes contains a huge amount of prior knowledge and context. Just compare the size of this comment in text bits vs. the (hypothetical) size of the knowledge you need (and have) in order to understand it.
If anything, saying that we communicate only 0.2MB per day illustrates just how huge this prior knowledge must be.
From an information theory perspective human communications might better be modeled as a compressed data stream with a very very big lookup table.
I'm not focusing on the overall channel bandwidth because I think it tells the full story, but it does tell an important story, and in particular, it shows just how constrained that channel really is. If we're sucking (or blowing) through a straw, then there's only so much information as can be mediated.
This becomes particularly significant when you look at the amount of crap that people are flooded with, and realise how much this cuts down on the ability to process significant and meaningful information.
It's literally true for what we are doing right now in this moment: emitting information through a keyboard.
But even then, it feels like we are doing much better than that. Maybe because we use implicit cross-referencing all the time.
The claim is that we _can't_ emit more than a few bits per second, and the rebuttal is that we can. Providing an example that's under the threshold is completely irrelevant.
I don't think that's true. Physical motion and even sound making in total involves a human being producing a lot more than a few bits of information per second - there are plenty of recordings of people singing, say, that can't compressed to that bitrate.
The only thing that's true is that we can pretty much only emit and absorb language information at a fairly low bitrate.
The simple explanation for this is that a language stream is something like a computer program - difficult to either produce or absorb.
And of course, language with complex structures is fairly unique to humans and provides some amazing things - the ability to help organize society and our own activity on a larger scale, to plan ahead, and etc, and etc, etc....
Edit: Good general discussion of these issues can be found in Tor Norretranders' book The User Illusion. Highly recommended.