More on the not-the-liver fallacy: medical, neuropsychological, and perceptual dissociations.

«...You are in the audience of a well-attended medical conference, about to listen to the highly regarded Dr. Fright. ‘I have a new discovery’, Dr. Fright begins. ‘I have isolated the organ system which removes toxins from the blood – I call it the ‘liver’’. Amidst oohs and ahs, Dr Fright provides some evidence for his discovery: ‘when this organ is removed from a rat, toxins quickly build up, and the rat dies’. Applause from the crowd. ‘But that is not all’, the lecture continues, «I have discovered a second organ. This organ circulates the blood, absorbs nutrients, expels waste products from the body, and attacks foreign invaders.’ ‘For when the liver is removed’, he argues, ‘the body is still able to do all these things and more, until such time as the toxin buildup is fatal. I suggest we call this second organ ‘Not-the-Liver’...’» (Bedford, 1997, p. 231). This fictitious story illustrates an erroneous conclusion. There is no second «not the liver» organ. Rather, the evidence shows merely that the liver is not the only organ in the body. While in this context the conclusion is clearly absurd, I claim the same formal conclusion is drawn routinely about «mental organs» (cf. Gall, 1791; Chomsky, 1975) from dissociation data. The Not-the Liver fallacy (NTL) refers to the erroneous conclusion that what remains after damage must be a coherent category, process, module, or natural kind. One example involves the universally known partition of memory into explicit and implicit components (Schacter, 1987, 1992). Implicit memory is founded on the NTL fallacy (Bedford, 1997). Damage to hippocampal structures produces a deficit in the ability to intentionally retrieve recently presented information while sparing the ability to do so indirectly or implicitly. A patient might fail to recall any words from a study list, or even that there was a study list, but then is more likely to use words from that list in various free association tasks. The NTL draws attention to the fact that while explicit memory is dissociated from «other stuff», the dissociation provides no way to understand that amorphous other stuff. The patient can also navigate the environment, perform mathematical calculations, show classical and operant conditioning, adapt to prism-displaced vision and so on and so on. There is no evidence that what remains following selective removal of one function is a coherent and meaningful category. Analogous to the way in which removal of the liver, or removal of an appendage, leaves merely person minus liver, or person minus arm, removal of explicit memory leaves only mind minus explicit memory.