But the trick of reading fast is tied to recognizing entire words, which spacemarks not only facilitate but create in the first place. Note that I say "space marks" above and "spacemarks" here, a decision not meaningful in classical writing.
One oddball consequence of my primary education was training in recitative, and it's a whole different beast, reading aloud. The texts were of course written normally, but I don't imagine a lack of whitespace would be such a burden, the attention is on the sound of the words and the meter of the sentence, it 'chunks' differently and with most of the focus on the cursor.
I originally put 'cursor' in quote marks in the preceding paragraph, before remembering, nope, medieval recitative was done with a literal object called the aestel in English. In medieval Latin this was called the "cursor manicula" or the running manicule (this is a manicule: ), since many were in the shape of a hand. The 'cursor' part carried over to the mobile line on slide rules, and thus became the computer cursor we know and love.
