This is a little beside the subject here but when I went through morse code training we had a former WW2 navigator/radio operator as an instructor. During endless hours of listening and transmitting on the waves he had developed a special sense for the rhytm of the various morse letters. Instead of perceiving these as dots and lines each letter had taken on its own expression. For example: A was tit-a, B was be-bib-bib-bib, C was Ce-ti-ce-tit......and so on. As you see each letter then contained the actual letter in this constellation. Further it was very easy for us newcomers to grab these dot/line constellations - and remember them. Actually, we didn't remember at all - it just sneaked in without any real plugging. The real beauty of this system was that the rhytm of the various letters transformed directly to the morsing finger. Transmitting was actually easier to learn than receiving. In this way we, in general, needed only 12 hours of instruction to be able to transmit/receive 120 signs per minute. Which was the aim.