Yeah. The choral effect is pretty well documented and is also a pretty interesting phenomenon. The theory that it supports is that one of the differences in brain function is about the auditory feedback loop. The part of the brain that looks out for errors in speech. For PWS / stutterers it's less efficient than in people who don't stutter. Having the other voice during choral speech helps with the auditory feedback. It's also one of the underlying theories for the Speech Easy and similar devices, which is a topic for a whole other thread.