Cognitive Computing 2012

1. Cognitive Computing 2012 The computer and the mind ASSOCIATIONISM Professor Mark Bishop

2. Idealism • The ‘ideal’ is the realm of mental ideas. • Contra ‘realism’ in which the ‘real’ is said to have an absolute existence prior to - and independent of – [our] knowledge. • Ontological idealism • insists that the only things that really exist are ideas. • Epistemological idealism • insists that the only things of which we can be certain of are ideas.

3. Platonic Idealism • Plato proposed an ‘idealist theory’ as a solution to the problem of universals: • A universal is that which things share in virtue of having some particular property • Cf. ‘Chair-iness’ and the archetypal chair. • Plato argued that it is only the universals - ‘the forms’ / ‘Platonic Ideals’ - that are really real … • … not particular individual things – instances – such as ‘this red chair’.

4. The ‘allegory of the cave’ • Plato imagines … • … a group of people who have lived all of their lives chained in a cave, facing a blank wall. • The people watch shadows projected on the wall by things passing in front of a fire behind them, and begin to ascribe forms to these shadows. • [According to Plato] the shadows are as close as the prisoners get to seeing reality. • Plato subsequently explains how the philosopher is like a prisoner who is freed from the cave who comes to understand that the shadows on the wall are not constitutive of reality at all • as he can perceive the true form of reality rather than the mere shadows seen by the prisoners. • The allegory is related to Plato's ‘theory of forms’, wherein Plato asserts that “forms” (or “ideas”) - and not the material world of change known to us through sensation - possess the highest and most fundamental kind of reality. • Only knowledge of ‘the forms’ constitutes real knowledge. • In addition, the allegory of the cave is an attempt to explain the philosopher's place in society.

5. Nominalism & Idealism • Confusingly, because Plato’s asserts that ‘the forms are genuinely real’, it is also called Platonic realism. • In this sense Platonic realism contrasts with nominalism • the notion that ‘mental abstractions’ are merely names without an independent existence; • the only thing that different chairs have in common is the name ‘chair’. • However Platonic realism is also seen as an early form of ‘Idealism’ • as it asserts the primacy of the idea of universals over actual instances of particular ‘material’ things.

6. British Empiricism:Hobbes (1588-1679); Locke (1632-1704); Hume (1711-1776) • The view that all ‘knowledge’ comes from ‘experience’. • That knowledge is causally dependent on experience. • That knowledge is justified solely by experience.

7. Subjective Idealism:Bishop Berkeley (1685-1753) • Like the Empiricists George Berkeley believed that all ‘knowledge’ comes from ‘experience’ (of our perceptions). • However unlike the Empiricists, Berkeley believed that only perceptions are ‘real’;if a tree falls in a forest with no one around, does it fall with a sound? • Scientifically: “Sound is vibration, transmitted to our senses through the mechanism of the ear, and recognized as sound only at our nerve centers. The falling of the tree or any other disturbance will produce vibration of the air.” • Philosophically: “To be is to be perceived”; is sound only sound if a person hears it? I.e. if no one is around to see, hear or smell the tree as it falls, how could the sound be said to exist? • But then why do different people share the same kinds of perceptions? • Berkeley, ‘God as the ultimate cause of all perceptions’.

8. Associationism and the British Empiricists • Associationism • The view that the mind is organized, at least in part, by principles of association. • Associationism is closely linked with the British Empiricist movement. • The core idea of Associationism is that items that ‘go together’ in experience will ‘go together’ in thought.

9. Associationism • Items are associated (go together) in the mind through a process of experience: • complex ideas are constructed from simples; • simple ‘ideas’ are derived from sensations/perceptions. • Sensations are not governed by association, but are caused from something outside the head: • for Hobbes, Locke, Hume, the ultimate cause of sensation are things in the world; • for Berkeley the ultimate cause of sensation is God.

10. Varieties of Associationism • Pure Associationism • Holds that only Associationist principles govern the operation of the mind. • Mixed Associationism • Holds that principles other than Association can have an influence on the mind.

11. The association or ‘going together’ of mental items • Mental ‘items’ can be associated by: • spatial contiguity; • temporal contiguity; • more abstract principles such as: • cause & effect; • similarity and contrast. • Suggested ‘items of association’ in the mind are: • memories; ideas; images; thoughts etc.

12. A Blank Slate? • For Locke in, An Essay concerning human understanding, (1690), the mind at birth is a ‘tabula rasa’ (blank slate). • There are no innate ideas, “Let us then suppose the mind to be, as we say, white paper, void of all character, without any ideas. How comes it to be furnished? I answer, in one word, from experience.”

13. Primary qualities • Example of primary qualities include: solidity; extension; figure; number; motion; rest. • The primary qualities have a direct link to their bearer; a primary quality ‘says’ something about its bearer. • E.g. If an object instantiates the primary quality of ‘rest’ then the object much be ‘at rest’. • Primary qualities are ‘essential’ to their bearers and are intrinsic qualities of their bearer. • I.e. Primary qualities are independent of the perceiving mind.

14. Secondary qualities • Example of secondary qualities include: colour; sound; taste; smell. • Secondary qualities are the powers of objects - by configurations of their primary qualities - to cause experience. • For Locke primary qualities exist in the world but secondary qualities exist only in the mind of the perceiver. • Thus, there is no blueness or sweetness in the world, only extension in motion.

15. Associationist Processes • Sequencing • Associations follow one another (eg. in time). • Compounding • Complex items are formed from simple items. • Decomposition • Complex items can be broken down into their simple elements.

16. Sequencing • Groups of items, (eg. memories), follow one another in one of two ways: • Intrinsic associations • Some items have a natural connection, (i.e. a connection independent of the observer). • E.g. Chilli peppers and ‘hotness’. • Extrinsic associations • And some items have an observer dependent connection, (either voluntary or by chance). • E.g. If the first person one fell madly in love with had long ginger hair then one may thereafter associate these qualities with beauty, sex and love.

17. Locke’s three properties of extrinsic association • Extrinsic associations are either voluntary or happen by chance. • The strength of the ‘impression’ of ideas can reinforce the association. • Powerful ideas may be forever linked in the mind (cf. perception of beauty). • Some items (contingent on say, genes) will ‘go together’ more easily than others • For example, some find associations with maths easy; some with football; others with singing etc. • So although at birth the mind is a blank slate (empty of ideas), individuals may find some ideas easier to associate than others.

18. Associationism • Mental representations are ideas. • We ‘entertain ideas’ when in mental states. • Hume suggested that mental processes are sequences of associated mental ‘ideas’, (‘associationism’). • But what are such mental ‘ideas’really about? • The problem of intentionality: how do ‘mental ideas’ connect with [become to be about] things in the world? • Hume suggested that mental ‘ideas’ are fundamentally like ‘images’. • Hence positing a ‘pictorial resemblance’ between idea and world; but this has problems.

19. Problems with Hume’s associationism • 1. Hume’s theory is both (a) too general; (b) not general enough. • a. Not all ideas are pictures • Justice? • b. Consider a picture of Eiffel Tower. • The image may look like the Eiffel Tower, from a certain perspective, but the image is not necessary to the notion of the Eiffel Tower (the tower that Gustave Eiffel built). • 2. No account of ‘mental reference’. • Resemblance is not sufficient for representation • A cartoon may look more like its creator than its subject, but still represent the subject. • 3. No account of truth and falsity • [Contra early Wittgenstein] Images are not propositions; • Images [in themselves] are neither true or false.

20. Associationism and representational theory • Cognitive processes are defined as, “associations between representations” • Associationism easily accommodates [folk] psychological explanations. • However Associationism lacks a workable account of ‘representational content’. • Representational content is whatever it is that constitutes a ‘representation of a dog’ as representing a dog rather than as ‘representing something else’; or rather than not being representational at all…

21. William James (1878)- The Principles of Psychology • For James thinking (all aspects of conscious life) had the following key properties: • Thinking is conscious. • Thinking is open to introspective examination. • Thinking is private. • ‘My thought belongs with my other thoughts and your thought with your other thoughts’. • Thinking ‘flows like a stream’ • The ‘stream of consciousness’; affect on literature – Woolf; Joyce etc. • Thinking is ‘about something’ (i.e. it is fundamentally “intentional”). • Thinking has evolved (thinking not as a ‘gift of god’).

22. What do we think next? • For James the key question in psychology is, ‘how does the mind solve the problem of what to think next?’ • His answer is that it operates on general principles of association which James attempted to illustrate on a deeper, quasi-neurological basis.

23. James, ‘On thinking’ (1) • Principle 1: • When two elementary brain processes have been active together or in immediate succession, one of them, on reoccurring, tends to propagate its excitement into the other. • NB. This principle is similar to the learning scheme outlined some years later by Donald Hebb.

24. James, ‘On thinking’ (2) • Second principle: • The amount of activity at any given point in the brain cortex is the sum tendencies of all the other points that discharge into it, such tendencies being proportionate: • to the number of times the excitement of each point may have accompanied the point in question; • to the intensity of the excitements; • to the absence of any rival point, functionally disconnected with the first, into which the discharges may have been diverted. • This principle is similar to the mathematical neural model outlined a few years later by McCulloch & Pitts.

25. Spontaneous thought • Spontaneous thought • 1. Unrestricted ‘total association’ between arbitrary concepts: • E.g. [the memory of] a walk followed by a romantic dinner. • 2. Partial association(s) • Not all memories are associated. • Why are some memories linked and not others? • 3. Focussed association / recall by similarity • Why might, say, thoughts of the moon lead to thoughts of football?

26. 1. Unrestricted associations • Consider the association of ‘walk’ followed by ‘romantic thoughts’. • Let [A] be the memory of the ‘walk’. • The pattern of excitement distributed across neurons [a,b,c,d,e]. • Let [B] be ‘romantic thoughts’. • The pattern of excitement distributed across neurons [l,m,n,o,p]. • Thus [A] must excite [B] • And [B] must excite [A]. • Hence James suggests the memories [A] and [B] ‘vibrate in unison’.

27. 2. Partial association • Only some past experiences have associated consequences. • James suggests four principles which determine which experiences are associated together; these are: • Habit: the more often something done the more likely it is to be associated. • Recency: more recent events are more likely to be recalled. • Vividness: the more intense an experience the more likely it is to be recalled. • Emotional congruity: Similar emotion backgrounds are more likely to be associated together. • E.g. Feeling miserable makes it more difficult to recall times of joy. • How these principles of association work: • If one is thinking A and A is associated with B, (by say habit), then one will subsequently think B unless a stronger principle applies. • At any time the strongest principle of association is that which pertains.

28. 3: Focalised recall / association by similarity • Think of the ‘gas-flame’… • And subsequent thoughts of the ‘moon’ [via a pale-whiteness; similarity of colour]… • Which, in turn, is linked to the thoughts of ‘football’ [via roundness; similarity of shape].. • So via focussed recall thought can moves from [A] to [B] (from gas-flame to football) even though neither [A] nor [B] have any properties in common.

29. Voluntary thought • Typically this is difficult for associationists; James tries to address the issue by showing how associationism can perform recall of a forgotten thing [and via the same mechanism] perform a form of ‘means-end’ analysis. • To recall a forgotten item: • Suppose memories [a,b,c] and [l,m,n] are all associated (& fully interconnected) with forgotten item [Z]. • Activation of [a,b,c] will eventually propagate to [l,m,n] and together [a,b,c, l,m,n] will activate [Z]. • Means-end analysis is performed in a similar way. • If [a,b,c] is the goal this will eventually excite suggestions [l,m,n] which together will excite the solution [Z]. • NB. James never considers if all reasoning is performed via means end or even if his version of means-end analysis will work in practise; consider balancing a bank account ...

30. The link between Connectionism and Associationism • Let input nodes to a ANN be sensory transducers (producing 'sensations'). • Let internal (hidden) network nodes encode ideas • Let inter-node weights indicate strengths between ideas • . • Let output nodes define behaviour. • … Then there appears to be a simple correspondence between Connectionism and Associationism.

31. Analysing the link between Connectionism and Associationism • Strictly speaking there are several ways in which this link breaks down: • In ‘Associationist Networks’ the items that get associated are specific idea(s). In local connectionist networks where one node encodes an item this also holds. However, in ANNs that use distributed encoding of knowledge this connection clearly does not hold. • In pure associationism ‘ideas’ are pure copies of sensations. In networks where weights from the input node are not unity [+1] this is not true - information is scaled by the weight value.. • NB. Associationism and connectionism can most easily represent the ‘arity zero’ predicates (propositions) of first order logic, (cf. Stochastic Diffusion Networks/NESTER).