Yeah, whatever. Call it a superpower if you want, but I used to boost my language scores by letting the audiotapes run at night for however long it took the walkman to hangfire. I'd gain about a grade level doing that. Sure, I'm already great at languages, but it's a lot easier to load grammar and pronunciation into the subconscious while the monkey is sleeping. No point making it harder than it needs to be.
Also, if you want to test sleep learning, then play things while people sleep and see if they learn better than a control group who's not doing that. Facts now, those aren't so easy to pick up. Languages and music seem to work fine. Possibly other things will work. But for fucksake, find out what specific things people are trying to learn in their sleep and test that, not abstract sounds.