I have no clue personally
, but it's interesting that we've been discussing similar issues in the dojo recently. From my Karate/Kempo days we were always taught to keep the hands closed, thumb tucked and it worked very well for striking, blocking, etc...However, based on purely anecdotal evidence, I seem to move better with a more open hand in Aikido. I think it helps to keep students from becoming too "grabby", or "choppy" too. I've noticed that Saotome Sensei, with whom my dojo is most directly affiliated, seems to use what I'll call a "hybrid hand" that's more, or less open with the middle, ring and pink fingers held somewhat more closely together while the index finger and thumb are somewhat spread apart from the rest. I'm not sure if it's conscious, or more incidental, but it is interesting and certainly seems to work.