I can't speak for psychological development, but from a personal experience, I can say that
1) D&D does keep my math skills from going dry
2) D&D increased my vocabulary many-times over as a young child (understanding the words used in the books and also because it got me to read other books more)
3) (as said above) It got me interested in reading more... fictional books, books about anthropology and sociology and evolution of that in cultures (like national geographic)
4) It got me to be more social with the "nerds" and, let's face it, nerds are good people to know - they are smart and stimulate your own mind
5) It got me to be more creative -- for any campaign I've ever run, or even for the small handful of freelance writings I did back in the day.. but it got my creative juices flowing and gave me an outlet for it
No it's never made me run out and seek cults to join or run in to caves thinking i can kill everything. I think those types of things aren't from D&D but rather someone already psychologically troubled and just latching on to D&D. But they could have just as easily latched on to anything (drugs, gambling, alcohol, weapons, sex, work, cleaning, reading, movies/tv, etc)
So, yeah, while I can't give you scientific evidence to the psychological effects, I can only say from personal experience that D&D has postivley contributed to my life in general
(Sure, it makes me a nerd in the process, but I'm okay with that)