“He didn’t process information in any conventional sense. He didn’t read. He didn’t really even skim. Some believed that for all practical purposes he was no more than semi-literate.”
I think that's a sign of senility more than anything else. There's been articles which show clips of his speech in the 1980s and 1990s. His vocabulary was much more extensive, and he used more complex sentences than the word salad he spews out these days.
