First a brief description of my very astute long-time student: Graduated from business school, employed in the fashion industry, no time to practice piano but deeply responsive to every sound, working on Bartok For Children Vol. I.
Today I showed her a facsimile of some Clementi and asked her to tell me what she sees. Answer: A lot of information tightly packed onto the page. Then she observed something I have been trying for years to put my finger on.
She said that a person reading at that time must have been able to process a lot of information, unlike the reading that she is doing in the Bartok. Then it hit me: An 18th-century player with sufficient keyboard skill to play Clementi would have had experience at the harpsichord on which single tones do not resonate, but on which many notes are required to give a satisfying sound. On the piano, however, the reverse is true: A single tone gives off such an amazing array of information that a single symbol connotes infinitely more than the corresponding symbol on an 18th-century page.
This is why it matters so much that reading be learned in terms of to auditory experience.