There's a bit of a schroedinger's cat problem in this kind of study, as I'm willing to bet people's physical responses change when they're subject to 'genital monitoring' as opposed to when they're alone.

There's a wonderful essay about just this kind of testing by David C Findlay called 'Survey Said'. It's published in the book 'First Person Queer', and possibly in a few other places, it's worth looking up.