Scientific justification for internal experiences is an interesting one. Sure it might get people on board, but for a subjective experience, there is nothing science could ever produce that could disprove said experiences.
Now, this is not to say that the interpretation of an experience's relationship to external reality can't be faulty or mistaken. If I have the internal experience of hearing the voice of god tell me to build a boat to survive a flood, and there's a drought when I'm loading the animals in two by two, we can all agree that I did not in fact hear the voice of any sort of omniscient being.
However, we can't deny that I experienced a voice in this hypothetical.
We could imagine doing a bunch of MRIs while I'm hearing that voice. And we could expect that they would show something going on then, that is the goal of psychology isn't it? But even if all things were normal, that is not evidence that I did not experience the hearing.
It's an internal experience. The only evidence one needs is the experience itself. Again, misinterpretation can happen. But the evidence would be plain as day to us: we had direct experiential access to the thing.
All the Theories and science in the world can be laid out, with suppositions on how mental states evolve and what causes a thought, but none of it can ever disprove a person's account of "this is what it's like in my mind."
If all of the scientific* evidence pointed to endogenic systems being impossible, they would have those internal experiences. Just like non-endogenic systems. Just like any internal experience. (Note* most of this discourse seems to forget that people's reports of their internal experiences are the foundation of the scientific evidence into what's going on in minds).
I like to share science because it's interesting. I like to show sysmeds studies because that's what they ask for. But at the end of the day, none of that proves the existence of plurality. Plurality is already proven simply by someone saying "I experience it."
You cannot disprove qualia.












