"You are quite right that my neutral monism is not 'pure'. I think that mental events only occur where there is a brain, or at least some kind of nervous system. My chief point, to which all other philosophers object, is that mental events have a location in space, in fact in the brain in the case of all higher animals, and, further, that they are constituents of the brain as well as of the mind." BR refers him to Human Knowledge, Part III.

"The main difference between sight and hearing, on the one hand, and the remaining senses on the other, is that the source of visual and auditory sensations is outside the body of the percipient, whereas touch, for instance, has its causal origin on the surface of the body of the percipient while such things as headache and stomachache have their causal origin inside the body. But all sensations, alike, are in the head. They differ only as to the physical location of their causes."