Answering Callahan's Visions

Since Gene Callahan has stopped posting my comments on his blog I'll reply here.

Gene made this remarkable statement:
"I don't know if Hildegard was having genuine revelations or not, but I do know that whether or not she was having migraines has nothing to do with answering the first question."

I pointed out that it does have quite a lot to do with "answering the question."
The issue after all is is whether we should say the visions came from god or something else. That's pretty much what "answering the questions" consists of.
It is logically possible that Arnold Schwarzenegger traveled back in time to show her flash cards, but if there is a simple, parsimonious natural explanation available we shouldn't accept that one.
And there is. Our eyes, optic nerves, and brain are a machine for seeing. This machine can malfunction, and see things that were not there. If I hit you on the head very hard and give you a concussion you might for a while see double. If you stare at the sun and walk into a dark room you still see a spot where the sun was.
We know that migraines  result in the sufferer experiencing light patterns.  This is a perfectly mundane explanation of why a 12th century woman might have seen light patterns. And it is not the only one possible.

  Gene dug in his heels with one remarkable bit of inconsistency.
"To turn that into 'God is the only explanation!' is really pretty bad. And note: that is absolutely not what they did in the Middle Ages! The Church was very skeptical of people who had 'visions,' and investigated very thoroughly before they would let anyone claim they were from God."
What I asked, in a comment Gene would not publish, did those investigations consist of?
Largely of ruling out simpler explanations. They decided she wasn't lying; they decided no neighbor has holding placards. Simpler explanations discarded. Twelfth century churchmen didn't consider neuroanatomy I'm guessing. They knew less about brains and vision than we do; our list of simpler explanations isn't constrained by their ignorance.

There is more along these lines. Enough to give one a headache.

Update:

"The tooth fairy came daddy!"

"Now Gene, you're over 50 years old, you shouldn't believe in the tooth fairy anymore. That was me. I snuck into your room while you slept and took your tooth."

"But he left a quarter daddy!"

"Now Gene, we've discussed this. I have a videotape of me sneaking into your room. Your mother is a witness. My fingerprints are on the quarter. I have your tooth in my pocket. I did it."

"That does not mean the tooth fairy didn't make you do it! He acted through you. So it's STILL the tooth fairy!"

"Now Gene, you know that you don't need the tooth fairy to explain my actions. They can be explained either by causation -- normal biological stuff -- or by my free will, depending on which you believe in, but in no case do I need to postulate a tooth fairy pulling my strings. Let's just leave aside talk of the tooth fairy."

"That's no proof! The tooth fairy could be controlling your every movement your every thought your every belief! He could be causing you to believe that you acted from free will, or physical causation, whilst it is he doing it all along! Disprove it!!"