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Lecture 5

Lecture 5 - end of Philosophical and Theoretical Background

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University of Toronto St. George

February 14, 2011  Final exam will include material from the entire course, but will focus more on everything after the first test Continuation of Philosophical and Theoretical Background Last two psychological frameworks are environmental/learning framework and evolutionary framework Environmental/learning framework  Inspired by John Locke  Basic mechanism to explain how development works  Learning drive by principles of association (Watson, Pavlov [classical conditioning], Skinner [operant])  Organism learns by principles of association (similarity, contrast, contiguity, frequency)  How do the criticisms of John Locke and his principles of association transfer into and become the criticisms of the environmental framework and classical and/or operant conditioning?  Even classical and operant conditioning are more sophisticated than previously thought  Pavlov o Alive during Russian Revolution o Criticized Stalin o Initially interested in studying digestion and salivation as part of the process of digestion o Performed surgery on dogs that allowed him to drain off and measure how much saliva they were producing under various conditions  Contrary to popular belief, he was very concerned about minimizing the animal’s suffering o Started to notice that salivation was elicited by “psychic factors”  Pavlov’s use of the word “psychic” = psychological o Sight of food can cause salivation, different foods causing different amounts of salivation – wow! o Put meat powder in dog’s mouths, along with sand. Why? Saliva is used for digestion AND to flush non-food particles out of your mouth. Very thick saliva is produced for digestion, thin watery saliva is produced to flush out things like sand. o Pavlov noticed that eventually the sight of meat powder or sand produced two different types of saliva. Dog’s behaviour was becoming conditioned by the sight of the food and the type of info the stimulus contained o Changed his line of research from physiology to psychology o Around 1907, starts to set up his conditioning experiment. Three stages:  Pre conditioning stage  Food elicits saliva. This aspect is not learned, doesn’t have to be taught. Unconditioned stimulus (US), unconditioned response (UR).  Also as part of preconditioning is a neutral stimulus (NS). Be careful – neutral doesn’t mean produces no reaction, it just means it doesn’t produce a response that is anything related to salivation. For example, metronome ticking. Dog can hear it, of course, but it doesn’t produce salivation.  Conditioning stage  Pair neutral stimulus with unconditioned stimulus. This pairing results in unconditioned response. Food and metronome together produce salivation. Contiguity, frequency, similarity, and contrast of the NS and the US determine strength of unconditioned response.  AFTER CONDITIONING  Neutral stimulus – Conditioned Stimulus = Conditioned response, NOT unconditioned response. They are NOT the same. At best, they are similar. Sometimes, they can be diametrically opposite. o When a rabbit sees a predator, first it freezes so it won’t be noticed anymore. This is the unconditioned response. o Pair a bell with the arrival of predator. Bell means there is a predator coming. So now when the rabbit hears the bell, it runs like hell. Unconditioned response is freezing, conditioned response is running like hell. Here is a case where the CR and the UR are hugely different.  What kind of properties of conditioning facilitate a neutral stimulus becoming a conditioned stimulus? o Frequency – more often Neutral Stimulus and Unconditioned stimulus are together, turns Neutral Stimulus into Conditioned Stimulus  This is the way the textbook presents things. Not accurate. We need to differentiate between appetitive and aversive conditioning.  Appetitive = US is pleasant, UR is seeking-out response  Aversive = US is unpleasant, UR is aversion  Aversive conditioning happens much more rapidly. Often only one or two pairings of NS and aversive stimulus will powerfully trigger a CR. o Signal detection theory: trying to get signal from the environment (information that is relevant to you). Signal is often polluted with noise (irrelevant information) zone when you can’t tell if signal is signal or just noise (uncertain, set a criterion of decision)  Mistakes:  Miss: very costly – gazelle hears a cheetah but thinks it’s just a noise, so it doesn’t run and it dies.  False alarm: much less costly – gazelle hears a noise and thinks it’s a cheetah when it isn’t, so it runs unnecessarily  No optimal way to always gamble  Aversive stimuli: much more likely for a miss  Negative situation: you don’t want to miss, lots of false alarms, set criterion really high – nature isn’t wiring you to be accurate, it just wants you to survive – sacrifice a lot of accuracy in order to increase chance of living  Something that indicates a predator once will become a powerful indicator. This is why gazelles (or other prey animals) are very skittish  The “cool” gazelle that won’t run ‘til its eye to eye with a cheetah will always be the dead one  Evidence that frequency does not drive association, internal constraints that bias the learning system o Contiguity = closeness in time and space o Temporal arrangement of stimuli  1. Delayed conditioning = NS terminated before the US  2. Trace conditioning = temporal gap between NS and US  3. Simultaneous conditioning = NS and US at the same time  4. Backward conditioning = US precedes NS. Allows no anticipation. Make NS biologically relevant. Shock + then ring a bell (rat example, shock than shadow of a snake, no natural
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