Psychology 354 Week 10: Functional Analysis

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1 Psychology 354 Week 10: Functional Analysis What is functionalism? What is functional analysis? Why does functionalism lead us to the functional architecture? The Tri-Level Hypothesis In the tri-level hypothesis, only one level is physical. The other two levels make novel predictions, but do not directly appeal to physical, causal laws What kind of descriptions are these? How can they be nonphysical, but still be predictive and scientific? An Abstract Example Edison s Chalk Relay In 1874, Western Union was going to use patent law to destroy their only competitor, the Automatic Telegraph Company. Western Union controlled the patent for the Page relay. This relay was based on magnets, and was used to amplify signals as they passed along the telegraph wire. A court was about to rule that ATC could not use the Page relay -- the only type in existence -- for a period of 17 years! To save the company, who does ATC call? The Page relay Edison invented a replacement for the Page relay, with identical connections Instead of using a magnet, Edison used a rotating drum of chalk that was driven by a small electric motor the motograph A needle rested on the drum; the friction between the needle and the drum changed markedly when an electric current flowed from the needle to the chalk This change in friction was a physical event that could be used to amplify the signal Thomas Edison ( ) and his motograph replacement for the Page relay Functional Equivalence Functionalism The two relays, though physically different, were functionally identical. Indeed, you could replace one with the other. ATC had been saved! From one of his pockets he took a pair of pliers, and fitted his [own motograph relay] precisely where the Page sounder had been previously connected, and tapped the key. The clicking -- and it was a joyful sound -- could be heard throughout the room. There was a general chorus of surprise: He s got it! He s got it! (Josephson, 1961) Information processing accounts can give the illusion of being profoundly nonphysical because they are functional in nature. They describe things in terms of what they do, not in terms of what they are made from! Page relay vs. Edison relay Real heart vs. Jarvik VII It s not that the physical doesn t matter it s just that many physical stuff s can do the same thing 1

2 Multiple Realization Functional Explanations Functionalism falls from the accepting multiple realization Different physical devices can be carrying out identical computations For example, many different physical systems can be used to construct Turing machines Babbage s difference engine is made from brass gears Denis Cousineau constructed a Turing machine out of LEGO Moises and Hoffman built a Turing machine out of an electric train set These systems are all physically different, but belong to the same abstract, functional class Babbage s difference engine A LEGO Turing machine An electric train that computes Cognitive scientists have a strong preference for functional descriptions For this reason, they use a methodology called functional analysis In functional analysis, a working system is decomposed into a system of smaller, organized, functional components Functional analysis does not appeal to physical properties software, not hardware! George Miller Karl Pribram Psychological Example Modal Memory Model Much of cognitive psychology s work on human memory can be viewed as being an example of functional analysis Memory Primary memory, Secondary memory Working memory, Semantic memory, Episodic memory, Sensory memory Central executive, visuospatial scratchpad, rehearsal buffer What evidence led to the proposal of this model in the 1960s? Free Recall Task Functional Dissociation Present to-be-learned list to subjects Read out one word at a time at set intervals At end, have subjects recall as many words as possible in any order Plot recall as a function of serial order in list Such data points to functional decomposition! Data can be used by cognitive psychologists to argue for functional decomposition Removing recency effect sound-alike words delay recall Such manipulations do not alter the primacy effect Removing primacy effect Present list quickly Use lots of synonyms These manipulations don t affect the recency effect 2

3 The Modal Model Ryle s Regress These functional dissociations led to the modal memory model Recency effect was due to short-term, lowcapacity, verbal store The primacy effect was due to long-term, highcapacity, semantic store More recent memory models elaborate this type of analysis Functional analysis is a fundamental tool in cognitive science Functional analysis is also the Cognitivist s Achilles heel In doing functional analysis, we take one functional term and decompose it into a set of other functional terms Philosopher Gilbert Ryle argued that this approach was doomed to fail, because it leads to an infinite proliferation of unexplained terms. This is known as Ryle s regress, or sometimes as the homunculus problem Gilbert Ryle Dawson s mental imagery system trapped in the homunculus problem Escaping Ryle s Regress Cummins Program How does a cognitive scientist, committed to functional analysis, extract himself or herself from Ryle s infinite regress? There must be some level of analysis which does not permit any further decomposition into mental state terms! Philosopher Robert Cummins has provided a detailed account of functional analysis which aims to escape Ryle s regress Define the function Analyze the function Subsume the function Robert Cummins Define the function being computed by the system Decompose this function into a system of subfunctions. Repeat as necessary to the subfunctions. Stop the decomposition when the subfunctions are so simple that they can be carried out by simple machines Functional Architecture When subfunctions are subsumed, they are said to be primitive They cannot be decomposed (functionally) any further These primitive subfunctions define a mental programming g language g This is called the functional architecture of cognition The special level at which functional decomposition stops The set of primitive processing operations The biologically fixed part of cognition The bridge between algorithm and implementation The set of functions for which behaviorism is true Can psychology subsume its functional theories? Yes! One example of a successfully subsumed theory in psychology comes from the study of color perception An Example 3

4 Maxwell s Proof Trichromatic Theory Maxwell used Newton s barocentric circle to prove that any color could be expressed as the sum of three other colors This was a computational analysis of color vision Maxwell s proof James Clerk Maxwell ( ) Helmholtz used the results of psychophysical experiments to come up with an algorithm for color vision This trichromatic theory was predictive, but was functional, not physical It must be confessed that both in men and in quadrupeds we have at present no anatomical basis for this theory of colors (1873) Hermann von Helmholtz ( ) Subsumption Comparative Cognitive Science The trichromatic theory was not subsumed until the 1960s Retinal pigments were isolated at this time, with different pigments corresponding to the different fibres Photons caused the pigments to change shape, resulting in the transduction of color signals Three types of photopigment Photons cause pigments to change shape The functional architecture must be identified and validated for a functional analysis to be considered an explanation The notion of functional architecture lets us now consider how models of cognition can be either strong or weak This is done by considering cognitive science as a comparative discipline Machine Intelligence? Turing proved the in principle power of information processing The power of the UTM made the notion of machine intelligence worthy of consideration How will we know if we have built an intelligent machine? Turing provided a behavioristic answer to this question in 1950 The Turing Test For 1 hour, the judge can communicate about anything to both participants. Then the judge must decide which participant is the program. If this cannot be done, then the programmed computer is deemed to be intelligent 4

5 ELIZA And The Turing Test The Weakness Of ELIZA Men are all alike. In what ways? They re always bugging us about something or other. Can you think of a specific example? Well, my boyfriend made me come here. Your boyfriend made you come here. He says I m depressed much of the time. I m sorry to hear that you are depressed. I need some help, that much seems certain. What would it mean to you if you got some help? Perhaps I could learn to get along with my mother. Tell me more about your family..what else comes to mind when you think of your father? Bullies. Does that have anything to do with the fact that your boyfriend made you come here? Joseph Weizenbaum ELIZA generates the right output for the wrong reasons It was a demonstration of how successful one could be in creating an apparently intelligent interactive system with relatively simple rules Two Equivalences Weak Equivalence Two systems are said to be weakly equivalent if they solve the same problem, but do so in different ways Eliza is a weakly equivalent system Two systems are said to be strongly equivalent if they solve the same problem, but do so in the same way Zenon Pylyshyn Equivalence Strong Equivalence Weak equivalence is sometimes called Turing equivalence Cognitive science requires a stronger equivalence Strong equivalence -- do the right things for the right reasons Strong equivalence -- run the same algorithm on the same architecture Cognitive science therefore needs to identify the functional architecture in order to subsume functional analyses, and to establish strong equivalence Zenon Pylyshyn 5

6 Discussion Topic Dawson hypothesizes that his pocket calculator is a strongly equivalent model of mental arithmetic What kind of evidence would refute this position? What kind of experiments could be conducted to collect this evidence? What kind of researcher would conduct these experiments? Evidence For Equivalence Error Evidence Does the model make the same kinds of errors as the subject? Relative Complexity Evidence Are different problems of the same relative difficulty for model and subject? Intermediate States Evidence Do the model and subject go through the same intermediate information processing steps? 6