Posted: 2013-08-23 11:34
the german psychologist Ludwig Koch has developed this system of training. I'll hope that you'll find more information about your question on this side:
http://www.qsl.net/n1irz/finley.morse.html N1IRZ was the first one who brought me in contact with Ludwig Koch. I have read his studies, but they are available only in german language.
A short answer to your question: The first intention was to find sound of letters that are mostly different from each other. And this for all letters that followed the last new one.
73, Mike, DF2OK
PS: Perhaps you can put this url http://www.df2ok.privat.t-online.de/afu01a.htm#KOCH trough the google translator and find some more details.