Let me preface all this by saying that I'm reasonably competent in ASL -- not fluent, but I don't tend to struggle too much with basic communication. I had learned some SEE first, before I understood the difference between SEE and ASL and opted for the latter when I was about 12 or 13 years old. (For a brief explanation of the differences see here; you could also show the Wikipedia love for entries on ASL and SEE.)
So, here's my scenario: Over the weekend I was away at a conference, and I met a deaf man who uses SEE; in an attempt to ease communication and mutual understanding, I tried to remember what I once knew of SEE, and by the end of the weekend was using SEE (rather than ASL) as much as possible. I would say I logged about 20 hours of singning, both in conversation and interpreting (I'm not an professional interpreter, by the way).
I made a few intersting discoveries as my SEE proficiency improved. First of all, I realized that I can only use SEE (instead of my normal ASL signing) when I'm looking slightly down and to the right, whereas if I'm trying to formulate thought in ASL, I look to the left and down... so I'm assuming I'm using different parts of the brain for each, and I'm wondering why. Secondly, I've noticed that when I'm typing, I've been transposing letters a LOT more than usual -- I've even typed a few words backwards today. I've also been mistakenly transposing words like "why" and "when." I have no idea what that might suggest, but it's been happening nevertheless.
I'd be interested to hear what anyone can suggest about the matter -- whether this is in fact indicative of some differences in brain fuction corresponding to the use of ASL or SEE, or if it has to do more with the process of mental translation prior to utterance... or something else entirely. It appears (after a quick Google search) that some of Ursula Bellugi's past research dealt with identifying ASL as a language in its own right, based that on the fact that related brain functioning originates from the left hemisphere. But that seems to contradict what I'm experiencing... unless SEE would not count as language use, but maybe as some other communication system?
Sorry for the lengthy post. Any ideas or suggestions of where I might find more information on the subject are greatly appreciated!!