I recently read a book called "What's Going on in There? : How the Brain and Mind Develop in the First Five Years of Life" and it actually talked about a study about spinning babies! I don't remember exact details, but I think the babies were even younger than yours. About once a week for several months, they would bring the babies in for a spinning session. They'd be held on someone's lap in a revolving chair and spin one revolution and the stop abruptly. They'd repeat this, holding the baby in different positions (vertical, cradled, etc.). The babies that were spun showed developmental gains later versus a control group. Maybe higher IQ? I don't remember exactly. I checked the book out from my library, maybe you can find it at yours!