Cognitive Computing 2012

1. Cognitive Computing 2012 The computer and the mind 6. IDENTITY THEORY Professor Mark Bishop

2. On ‘mental causation’ … • Descartes, holding that mental events/states of res-cogitans are non-material, believed the point of interaction (between the mental and physical) was at the pineal gland. • Against this modern physics, viewing the universe as a closed system, suggests the notion of any such ‘non-physicalist’ interference is incoherent. • ‘Physicalism’ is a philosophical position holding that everything which exists is no more extensive than its physical properties; that is, that there are no kinds of things other than physical things. • Because it claims that only physical things exist, physicalism is generally considered to be a form of monism. • Hence Davidson, working with this assumption, has argued that in order for mental states to produce their physical effects they themselves must themselves be – in some form – identical with the physical. (c) Bishop: The computer and the mind

3. Eliminative materialism • Eliminative materialism (also called eliminativism) is a materialist position in the philosophy of mind dating from the 1960s-70s and is the idea that certain classes of mental states that commonsense takes for granted – beliefs; desires; subjective sensation of pain; etc. – do not exist. I.e. • Descartes famously challenged much of what we take for granted, but he insisted that, for the most part, we can be confident about the content of our own minds. • Eliminative materialists go further than Descartes on this point, since they challenge of the existence of various mental states that Descartes took for granted. (c) Bishop: The computer and the mind

4. Eliminativism • Eliminativism about a class of entities is the view that that class of entities does not exist (contra reductionism where one class of entities can be reduced to another). • Thus for example: • In a monatomic gas ‘temperature’ can be reduced to the ‘kinetic energy’ of its atoms as they move/vibrate. • In contrast all forms of materialism are eliminativist about ‘the soul’; it does not exist! • modern chemists are eliminativist about ‘phlogiston’ (hypothetical element at the heart of the oxidisation processes of rust and fire); it does not exist! • modern biologists are eliminativist about ‘élan-vital’ (the vital spark); it does not exist! • modern physicists are eliminativist about the existence of ‘luminiferous aether’ (an aether for the propagation of light); it does not exist! (c) Bishop: The computer and the mind

5. Eliminative materialismcf. the Churchlands, Dennett & Rey • Eliminative materialism primary claims are: • that people’s common-sense understanding of the mind (or folk psychology) is false and • that the neurosciences will one day reveal that the mental states that are talked about in everyday discourse - using words such as "intend", "believe", ”pain", and "love” - do not refer to anything genuinely distinctly real (above the brain). • Patricia churchland stated, (1986), that “it is hard to see where in the brain we are going to find anything that even remotely resembles the sentence-like structure that appears to be essential to beliefs and other propositional attitudes”. • For the ‘eliminative materialist’ there are only ‘tuples’ of ‘neural firings’ … • Only because of the ‘inadequacy of natural languages’, people mistakenly think that they have such beliefs and desires. (c) Bishop: The computer and the mind

6. Versions of eliminative materialism • The most common versions of eliminative materialism are: • Eliminativism about propositional attitudes; as expressed by Paul and Patricia Churchland; • A propositional attitude is a relational mental state connecting a person to a proposition, e.g. 'Sally believed that she had won‘. • Eliminativism about qualia / subjective experience; as expressed by Daniel Dennett and Georges Rey. • Dennett suggests that part of the reason we may have difficulty replicating pain in computational systems is because our concept is so defective that it picks out nothing real; in certain conditions, drugs like morphine cause subjects to report that they are experiencing excruciating pain, but that it is not unpleasant; what is pain if it’s ineffable quality can be inverted in this way? • Thus the Churchlands are eliminativists when it comes to propositional attitudes, but reductionists concerning qualia; whilst Dennett is a reductionist with respect to propositional attitudes, and an eliminativist concerning qualia. (c) Bishop: The computer and the mind

7. The need for mental states • However persistent problems with behaviourism and simple stimulus-response theory suggest that inner mental states are required to explain behaviour; for example: • In classical behaviourism the ‘belief’ that aspirin cures headaches is a simple behavioural disposition to take aspirin whenever a headache arises. • But this implies equating a belief – e.g. that aspirin cures headaches – to the behavioural disposition. • But of course I might believe aspirin cures headaches yet always still always take Paracetamol, (because, say, of a stomach ulcer). • Mental states or events - e.g. desires and beliefs – thus contribute causally to the bodily movements involved in action, but do not equate to (nor can not be reduced to) simple behavioural dispositions. (c) Bishop: The computer and the mind

8. Epiphenomenalism- as a species of dualism • Descartes interactionist dualism held that mental states and events exist and both cause [and are caused by] physical events. • The epiphenomenalist holds that mental states and events do exist and are caused by physical events although they do not themselves cause physical events. • The epiphenomenalist then can accept that there are no causal influences on physical events besides other physical events, and thus can escape one objection sometimes raised against dualism. • But the epiphenomenalist’s picture - of mental states and events ‘tacked on’ to the physical without causal influence – remains a tad unappealing. (c) Bishop: The computer and the mind

9. Union theory: the neural correlates of consciousness • Union theory concerns the relation between mental events and neural events, and their combined causal efficacy, (cf. Honderich). • The ‘correlation hypothesis’ holds that all types of mental event are nomically correlated (a law-like association not strict identity) with types of neural events: • The relation of two events is such that the first necessitates the second and the second is necessary to the first… • “my thought of London a moment ago stood in a certain tight relation with a certain neural event, and if another event of exactly that type occurs, I or somebody else will be thinking of London in exactly the same way.” • Hence 'psycho-neural' correlates are pairs. • Further, the correlation is most likely to be that of one type of mental event with one of many types of neural event. • The Union Theory implies a causal role for such a ‘mental-neural union’ with respect to subsequent physical actions or mental events. (c) Bishop: The computer and the mind

10. Central state materialism- cf. Place; Smart • Inner mental states exist, are responsive to external stimuli and causally explain behaviour. • These inner mental states are simple material (physical) states of the nervous system. • Central state materialism posits an identity of mental state and brain state only to those cognitive and volitional concepts resilient to behaviourist treatment. • Notably consciousness, sensations; mental imagery.. (c) Bishop: The computer and the mind

11. Identity theory- cf. Armstrong • Identity theory proper holds that all states and processes of the mind are identical to states and processes of the brain. • Identity theories provide a comprehensive account of mental causation as each mental event is identical with a physical event, not merely correlated with brain processes: • Visible light is electromagnetic radiation (of particular wavelengths). (c) Bishop: The computer and the mind

12. ‘Token’ mind-brain identity • Token theory is synonymous with property dualism; each token mental phenomenon is identical with an instance - or token - of a specific physical (neural) phenomenon. • One substance – the brain – has two properties: mental properties and neural properties. • A specific pain (e.g. the pain of a 2lb hammer-head hitting your thumb with a specific velocity) is a specific neural event in our (carbon based) C-fibres of the brain. • Hence a hypothetical Martian (with silicon based, S-fibres) on hitting his thumb with a hammer in exactly the same way, would not feel identical pain to our hammer wielding human (with our carbon based C-fibres). • For two pains to be identical they must be realised in identical material. • Hence no two humans who say, hit their thumbs with a 2lb hammer in exactly the same way, would feel the exactly same pain; unless their brains were identical. • Yet even the brain structure of two identical twins is not exactly the same; hence no two humans can feel exactly the same (hammer) pain. (c) Bishop: The computer and the mind

13. ‘Type’ mind-brain identity • Each type of mental phenomenon is identical with a type of physical phenomenon. • Each type of sensation, (e.g. say, the human pain of hitting your thumb with a hammer), occurs when certain types/groups of (carbon based), C-fibres fire. • Thus ‘type’ identity characterises general types of mental event (say the human sensation of pain in hitting the thumb with a hammer) as specific types of C-fibre activity in the brain. • It implies a form of ‘token’ identity, (if exactly the same neurons fire, then the same pain must result). • Hence in principle, our Martians (with only S-fibre brains) could not feel the same types of pain as Humans with our C-fibre brains. • But two humans with the same type of C-fibre firings could feel the same type of pain. (c) Bishop: The computer and the mind

14. Psychophysical bridging laws • In the ‘type’ version of mind-brain identity theory ‘bridging laws’ are putative natural laws reporting regular or necessary relationships between mental states and events and physical states and events (brain states & processes). • On the ‘token’ version of the mind-brain identity theory it is less plausible that there could exist such psychophysical bridging laws. • Because, although any token mental event is numerically identical with some token neurological event, it does not follow that qualitatively similar mental events are numerically identical with qualitatively similar neurological events. (c) Bishop: The computer and the mind

15. Reductive and non-reductive physicalist identity theory • Reductive physicalism is a strict form of monism where the mental is ontologically reduced to the physical. • Thus, in a reductive form of identity theory – contra property dualism - the mental is ontologically reduced to brain states. • Such ‘reductive physicalism’ is not incompatible with eliminativism - the view that mental/psychological states do not exist at all. • In a non-reductive physicalism while mental states are physical they are not reducible to physical properties. • Donald Davidson proposed ‘anomalous monism’ as non-reductive physicalism. • Mental events are identical with physical events, and that the mental is anomalous, i.e. under their mental descriptions mental events are not regulated by strict physical laws. • Hence, anomalous monism is an identity theory of mind without the reductive bridge laws associated with the standard type-identity theory. • David Chalmers introduced a ‘Principle of Organisational Invariance’ bridging law as a form of non-reductive physicalism with respect to conscious mental states • Although the mental is not reducible to the physical, any system with appropriate ‘fine grained functional organisation’ will instantiate appropriate mental states. (c) Bishop: The computer and the mind