Presentation on theme: "Cognitive Computing 2012 The computer and the mind FUNCTIONALISM Professor Mark Bishop."— Presentation transcript:
Cognitive Computing 2012 The computer and the mind FUNCTIONALISM Professor Mark Bishop
01/04/2014(c) Bishop: The computer and the mind2 Physical supervenience Supervenience is a kind of dependency relationship, typically held to obtain between sets of properties. Supervenience has traditionally been used to describe relationships between sets of properties in a manner which does not imply a strong reductive relationship. E.g. Economics supervenes on physical properties of the world; two identical worlds will instantiate the same economic properties but this does not imply that economics is reducible to physics in any straightforward way. A group of properties X supervenes on a group of properties Y, exactly when the X-group properties are determined by the Y-group properties but X-group properties are not fully reducible to Y-group properties. Property (X), supervenes on a property (Y), iff there could not be a difference in property (X) without a difference in property (Y).
01/04/2014(c) Bishop: The computer and the mind3 A formal definition of supervenience X-group properties supervene on Y-group properties if: (a) X-group properties are not fully reducible to Y-group properties AND (b) iff any one of the following holds for all property bearers a and b: a and b cannot differ in their X-group properties without also differing in their Y-group properties. If a and b have identical Y-group properties, then they also have identical X-group properties. If a and b do not have identical X-group properties, then they also do not have identical Y-group properties.
01/04/2014(c) Bishop: The computer and the mind4 On the supervenience of acceleration, velocity and position A very widely used example of supervenience (e.g. online Dictionary of Philosophy of mind) is given in the relations between the acceleration, velocity, and position of an object in space. An object cannot change its acceleration without changing its velocity, and in turn, cannot change its velocity without changing its position. An important feature of supervenience illustrated by this example is that the supervening properties need not be identical to the properties upon which they supervene. Thus, acceleration supervenes on velocity, but is not the same thing as velocity. But (pace Newton) is acceleration fully reducible to velocity ?
01/04/2014(c) Bishop: The computer and the mind5 The transitivity of supervenience relationships In the previous widely used example of supervenience, facts about an object's acceleration supervene on facts about an object's velocity which in turn supervene on facts about an object's position. The illustrates an important feature of supervenience, namely, that supervenience is transitive. A transitive relationship is a relationship between three elements such that if the relationship holds between the first and second elements and between the second and third elements, it necessarily holds between the first and third elements. NB. Other examples of transitive relationships are equality for numbers and divisibility for integers.
01/04/2014(c) Bishop: The computer and the mind6 On the supervenience of the mental The fact that supervening properties need not be identical to their subvening properties is the source of the great appeal of supervenience to many contemporary philosophers of mind who hold that … The mental cannot be identical with the physical (largely due to considerations of a lack of multiple-realisability); I.e. The problem of Martian pain under either version of identity theory. … and yet want to remain physicalists! And thus hold on to the notion that the mental is determined by the physical.
Local and global supervenience Local supervenience B-properties supervene locally on A-properties if the A-properties of an object determine the B-properties of the object. E.g. Two objects with the same physical properties will have the same shape. Global supervenience B-properties supervene globally on A-properties if the A- properties of the entire world determine the B-properties. E.g. Paper notes and value. 01/04/2014(c) Bishop: The computer and the mind7
Logical and natural supervenience B-properties supervene logically on A-properties if no two logically possible situations are identical with respect to their A-properties but distinct in their B-properties. A logically impossible situation is not conceivable without violating laws of logic. E.g. A male vixen is logically impossible; a flying telephone logically possible. B-properties supervene naturally on A-properties if no two naturally possible situations are identical with respect to their A-properties but distinct in their B-properties. A naturally possible situation is a real [empirical] possibility. E.g. A mile high skyscraper. 01/04/2014(c) Bishop: The computer and the mind8
01/04/2014(c) Bishop: The computer and the mind9 Aesthetics: the beauty of Michaelangelos Moses For example, a computer prints copies of Michelangelos Moses on two different coloured sheets of paper. If, (in this world at least), irrespective of the colour of the paper used, (the property bearer), the form of the sketch remains beautiful, we say that its beauty supervenes on the print. We say that the sketchs beauty is an abstract property which naturally supervenes on the physical molecules of the coloured page. Hence, in aesthetics, we might say that the beauty of Michelangelos Moses supervenes: on the physical composition of the painting (the specific molecules that make up the painting), the artistic composition of the painting (in this case, dots), the figures and forms of the painted image, and on the painted canvas as a whole.
Supervenience and money The value of a piece of paper money does not supervene on the micro-features of the paper it's made out of. The value of the paper money is not just determined by micro-features of the printed paper, but also by a broader distribution of social facts and institutions. Thus the low level features of the paper alone do not determine the value of the money. Hence supervenience does not obtain between monetary value and the physical properties of paper money. Albeit value clearly does supervene between money and the wider physical world [which includes the relevant socio-economic institutions]. 01/04/2014(c) Bishop: The computer and the mind10
Aesthetics revisited: Duchampsfountain Fountain is a 1917 work widely attributed to Marcel Duchamp The work was a porcelain urinal, which was signed "R.Mutt" and titled Fountain. The work is regarded by some art historians and theorists of the avant- garde as a major landmark in 20th century art. Replicas commissioned by Duchamp in the 1960s are now on display in a number of different museums. Clearly the value of a porcelain urinal does not merely supervene on its physical properties.. 01/04/2014(c) Bishop: The computer and the mind11
01/04/2014(c) Bishop: The computer and the mind12 Supervenience and functionalism Functionalist theories identify what they do by their function, not by their form or substance. Functional states supervene on physical states. Thus, if the physical properties of a system are identical, then their functional properties must be identical. But equally these functional properties could be realised in different physical ways. Thus a mousetrap could be made of plastic or wood; it could be wooden spring-loaded mouse killing machine or a clear plastic-corridor trap.
Hilary Putnam The Computational Theory of Mind (CTM) came to the fore after the development of the stored program digital computer in the mid-20th century Through machine-state functionalism Putnam rst embedded the RTM in a computational framework. At the time Putnam famously held that: – Turing machines (TMs) are multiply realisable on different hardware. – Psychological states are multiply realisable in different organisms. – Psychological states are functionally specied. 01/04/2014(c) Bishop: The computer and the mind13
Computational theory of mind Putnams 1967 conclusion is that the best explanation of the joint multiple realisability of Turing Machines (TMs) and psychological states is that: TMs specify the relevant functional states and so specify the psychological states of the organism; Variations on CTM structure the most commonly held philosophical scaffolds for cognitive science and psychology e.g. providing the implicit foundations of evolutionary approaches to psychology and linguistics. Formally stated the CTM entails: – Cognitive states are computational relations to computational representations which have content. – A cognitive state is a state [of mind] denoting knowledge; understanding; beliefs, etc. – Cognitive processeschanges in cognitive statesare computational operations on these computational representations 01/04/2014(c) Bishop: The computer and the mind14
01/04/2014(c) Bishop: The computer and the mind15 Functional theories of mind Functionalism entails that every type of mental state, event or process, is simply a functional type of state, event or process of the system. Functionalism about cognition, concerns functionalism about cognitive states (such as beliefs, desires etc). Functionalism about consciousness, concerns the phenomenal experience of such states (the subjective feel of pain etc). But if mental properties are functional properties, then mental properties must also supervene on the physical. As the functional properties supervene on the physical.
01/04/2014(c) Bishop: The computer and the mind16 Properties of functionalism Like behaviourism, functionalism is firmly grounded in the observable. But unlike behaviourism, functionalism gives causal power to internal states of the system. By identifying mental states with functional states (i.e. a version of an identity theory) and noting that functional states supervene on physical states, functionalism defines a kind-of causal role for mental states. Also, (in common with type identity theory), functionalism allows the characterisation of different types of mental state. An attractive property of functionalism is that it allows for themultiple realisability of cognitive states: Silicon based Martians could have the same pains as humans. S-Fibres perform the same function and induce the same pain as C- fibres.
01/04/2014(c) Bishop: The computer and the mind17 Epiphenomenalism - as a species of functionalism One objection to functionalism about cognition, (eg. Jacksons Mary), has it that a causal account of cognition omits something crucial to some mental states.. The missing ingredient is the intrinsic phenomenal nature of mental states. These subjective features of experience, qualia, are accessible only from a first-person perspective. Some functionalists, such as Chalmers, concede this objection and attempt to develop a [non-reductive] functionalist account of consciousness, Hence subjective features of experience, qualia, are acknowledged… But such qualia remain merely epiphenomenal.
01/04/2014(c) Bishop: The computer and the mind18 Non-reductive functionalism - Chalmers (1996) A theory of consciousness should, give the conditions under which physical processes give rise to consciousness, it should specify just what sort of experience is associated. And we would like the theory to explain how it arises, so that the emergence of consciousness seems intelligible rather than magical. Chalmers argues that, consciousness can only be understood within a non-reductionist science of the mind. Consciousness is naturally supervenient but not logically supervenient on physical states of the brain.
01/04/2014(c) Bishop: The computer and the mind19 Chalmers Principle of Organisational Invariance, (POI) Ontologically Chalmers asserts a kind of property dualism; in our world (but not in every possible world) there are: Physical properties; Phenomenal properties. For Chalmers (in our world) there are pheno-physical bridging laws between the phenomenal and the physical. In our world (but not in every possible world) any system with the right kind of functional organisation will be conscious: The POI: For any system with conscious experience, a system with the same fine grained functional organisation will have qualitatively the same phenomenal experience.