As a psychology major, I will say that asserting "luminance only picutres do not get sent to the brain's visual lobes..." is bordering on rubbish.

At night, our cones are largely inactive and thus we are effectively only seeing with out rods, or "luminance" receptors. Does this mean that our visual cortex is not stimulated? Heck no! Any signal from our eyes will be sent to our visual cortex; afterall it's vision.

And just because we are looking at a black & white print, it does not mean we are somehow only seeing luminance. We are still seeing color, granted the subject is relatively neutral, but our cones are doing the heavy lifting even when looking at b&w.

I think it's a beautiful analogy about the power of black & white, but from a physiological standpoint it doesn't hold water.