My brain does some fancy post-processing of the optical data and presents me with the perception of A being darker than B. I can form beliefs about what underlying physical reality might cause this perception, and I expect to continue experiencing it. Separately, I could measure the luminosity of the two regions and get a perception of two equal numbers. When you tell me about the illusion, that changes my expectation of what sorts of luminosity numbers I will perceive, but it doesn’t change my expectation that I will continue experiencing apparently-differently-colored regions in my visual field. All this means is that I shouldn’t expect my visual field experiences to always match my luminosity sensor output experiences.
My brain does some fancy post-processing of the optical data and presents me with the perception of A being darker than B. I can form beliefs about what underlying physical reality might cause this perception, and I expect to continue experiencing it. Separately, I could measure the luminosity of the two regions and get a perception of two equal numbers. When you tell me about the illusion, that changes my expectation of what sorts of luminosity numbers I will perceive, but it doesn’t change my expectation that I will continue experiencing apparently-differently-colored regions in my visual field. All this means is that I shouldn’t expect my visual field experiences to always match my luminosity sensor output experiences.
To clarify, by “my brain” I’m referring to the specific subset of my brain that does sensory processing below the level of conscious experience.