Just skimming through the responses, i had an idea. Why don't you flip your thesis? You could explore how perception is the only thing that matters, and that the source of the sound doesn't matter at all.
For example, you could fabricate an effect from some other source, but make it emotionally realistic (ie. fitting the drama, and the world of the film). An example could be something as simple as a door slam made from a processed cannon and 2 pieces of wood slapping together.
On the other hand, you could use an effect that is a literal recording of what you're seeing on screen. Some doors have pretty lame slams in "reality". The door thing is just an example. It's also important not to deliberately cripple either side of the experiment - make both as effective as you can; just use physically real sources for one, and emotionally real sources for the other.
Then you could see which ones stand out to the audience as "wrong", in an effort see whether emotional realism is the most important thing, rather than sound sources. The tricky thing is managing your feedback. I find that it's not useful for non-sound people to focus on listening; if you tell someone to listen for something, it's easy for them to convince themselves they're hearing it. Maybe you could make your sequence short and concise, and then ask them questions about it after the fact.
Anyway, i hope there's something helpful in there. Just something that occurred to me. Best of luck!