[tadfisher]

I have a suspicion that 90% of the functional effectiveness of any visual aesthetic is learned experience. Witness the outcry over 48fps feature-length films, for example; people complain that it has a "cheap" or "soap-opera" feel, because cheap productions and soap operas are the dominant media filmed in high-speed. This affects the enjoyment that movie-goers take out of their experience, and thus the overall value of the product.

The inferences we make about functional differences in the aesthetics of type would clearly be biased by this phenomenon. It might certainly be possible for controlled observations to reveal that reading speeds are faster for serif type; but this might be due to the fact that the reader is used to it, as most long works are already printed in serif type, in part due to the assumptions of book designers that serif type is faster to read!