Since roughly 1960, the typographical style has shifted from two spaces after a period to one space after a period. Some people have claimed that the old convention of two spaces can improve speed reading.
Found in comments for the same article:
I am a speed reader (trained and practicing).
Comprehension being equal, I can read faster with double spacing between sentences. It is a tested and quantifiable fact, and this is generally true for the majority of speed readers.
And also here:
[Speed readers] read in word "chunks" or "grabs", but doesn't that actually suggest that double-spacing after periods improves readability? Most people absorb maybe two to three, perhaps up to five words per "chunk", not two or more sentences per chunk. Having sentences separated by spaces would make it easier to "grab" the words in related groups according to sentence structure.
I also remember reading a claim on Facebook that "studies" show that double spaces improve speed reading, but I can't find that claim any more. The first quote above seems to suggest the same, though (talking about the "quantifiable fact").
Are there any studies which actually show this claim to be true?
It has been brought up in comments below that "speed reading" is not a well defined term. For the purpose of this question, I'm willing to entertain any reasonable definition of the term, even possibly including "self-identified speed readers." But I do expect an answer to specifically address "speed readers", since the claim clearly makes the distinction between "speed readers" and the implied "average" or "non-speed reader".