Note that I mentioned experience due to only "mental activities". For instance, what is our first person experience of solving a math puzzle or writing a piece of good code or a beautiful poem? Does it require any sense organs to have this first person experience of authoring, creating, or solving problems?

Furthermore, even when it comes to sensory activities such as seeing, smelling etc., don't we have first person experience of such activities in dreams when all the sense organs are shut out completely? Of course this is not what I intended with first person experience of purely mental activities, but it is also something to ponder upon.