If it wasn't for religion

[Dr H]

Actually I was thinking of direct brain stimulation of those parts of the brain which are active when you do perceive a cup that is actually there.  This could be done electrically, with certain drugs, and possibly magnetically.

And, of course, there's hypnosis and other forms of suggestion.

Optical illusion was not at the top of my list.

Sure, like a brain in vat scenario, or us living in the matrix.

No, more like the way your brain actually works.
Through electrochemical processes.

Your brain can't tell the difference between you seeing a cup sitting on a table,
and me stimulating the same parts of your brain, in the same way, with electrodes
to make your brain think it's seeing a cup sitting on a table.

If they were true would cast doubt all of perceptions and experiences. But absent of any defeater, like some compelling factor to make me think im a brain in vat, I have no reasons to doubt my sense experiences.

All perceptions are doubtful.
All experiences are subject to interpretation.

Welcome to Real Life™.