Quite a bit.
Studies on human sexuality in any form are always associated with a bit of professional stigma - people who study it generally don't broadcast it to the media, and often even take pains to disguise it in sterilized medical jargon so as to prevent curious attention from laypeople being directed at it. As might be expected, the public has a habit of demonizing the scientists who do so and suspecting them of being all sorts of perverts for studying such a thing.
But there have been studies conducted for just about everything you can think of having to do with heterosexuality, and homosexuality, and autoeroticism, and just about every way we humans get off. If you're actually interested in a survey of the topic, I would recommend the popular science book "Bonk" by Mary Roach.