In reply to White spaces:
Hrant, how many times do we have to go round this: No matter where you measure it, there's no pattern of flow (AKA rhythm) at the letterform level.
You are the only person in any of these discussions who equates rhythm with flow. You persist in speaking about rhythm as if we were talking about it as an aspect of reading, when it is obvious that Bill and Peter and I and others are talking about is rhythm as an aspect of what is read, i.e. not of the processing but of what is processed. Your comment about saccade length is, therefore, a red herring, because we're not talking about rhythm of saccades but of what is perceived during fixations. Peter is simply correct: narrow phase alignment of blacks is an observable and measurable feature of the Latin writing system in general and Latin text types in particular. You can debate what role this plays in reading and readability -- and even suggest that deviating from it might improve readability, although I think there are good reasons to doubt this --, but calling it an illusion is silly.