https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3808979/
https://pubmed.ncbi.nlm.nih.gov/17097347/
People with either are less likely to experience illusions. SlateStarCodex had a decent article that touched on the phenomenon a few years ago:
https://slatestarcodex.com/2017/06/28/why-are-transgender-pe...
i can tickle myself reliably and in a bunch of diff places but pretty sure i'm otherwise normal. not a schizo not an autist so idk why... or at least pretty sure i'm not (◕‿◕)
On the other hand, I've noticed a fair number of other strange reactions that I sometimes get to sensations that I've occasionally seen other people online mention but have never met anyone else in person who also says they have them. One weird one is that when certain things vibrate in my hand (e.g. some but not all of the cell phones I've had and my Nintendo Switch's "rumble"), my inner ear will feel like it's shaking around, which is very unsettling. It seems to happen on the opposite ear of the hand my phone is being held (or both ears if both hands are touching). I can also sometimes replicate it by tickling parts of my lower face (in which case it happens on the same side as the part of my face touched), which makes me think it's due to some sort of actual physiological response to some extent rather than just some sort of weird resonance). From googling this in the past, there do seem to be other people who experience this, but I couldn't find any sort of documented research on it (presumably due to it being rare and benign enough not to merit anyone's attention).
Source?
The hypothesis is that people with schizophrenia are less able to predict their internal sensations - and because tickling is so tightly coupled exciting our brains expectation and predictions - they experience it as if someone else is doing it.