[jerf]

The number of "bits" something takes is not an absolute value. It is relative to the encoding scheme that is being used for the bits.

Converting a large word list to a small number of bits has been a computer science hobby for a long time. Here's a pretty good search result to start working through for more details: https://duckduckgo.com/?q=building+a+small+spell+checker+suf... It was especially important to write small and fast spell checkers in the 1980s and early 1990s, when you couldn't expect to have enough RAM sitting around to simply load up a naively-encoded list of words, and the act of spell checking a few thousand words could take noticeable time.

So in an encoding scheme chosen to represent English compactly, I'm not too surprised that you can get things down quite small.

However, the question is, what relevance does that encoding scheme have to the human brain? Having just scanned through the paper, the answer is "probably not that much", which the researchers are well aware of. They explicitly present this as a lower-bound, which is a reasonable thing to do. It is obvious that the brain does not simply store 1.5MB of data in the way a computer does, in many ways.

To be honest, this amounts to an exercise in recreational mathematics more than anything else. There's nothing wrong with that, and that's not a criticism. My point is that I'm not sure it's worth trying to read the paper as anything else.