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Lecture 6

Lecture 6+7 Instrumental Conditioning.docx

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Department
Psychology
Course
PSYCH 1X03
Professor
Joe Kim
Semester
Fall

Description
Psychology Lecture 6/7: Instrumental Conditioning Bernard Ho October 2, 2010 Instrumental Conditioning  Definition o Learning the contingency between behaviours and consequences  Thorndike’s Experiment o Put a cat in a box with a rope attached to the door o Food was placed outside the box o Thorndike recorded behaviours and escape times of cat  Hypothesis was that at first, the cat would show random behaviours in figuring how to escape the box  By accident, the cat would find the rope that opened the door during one trial  After that one trial, the cat would learn the contingency between the rope and the door  Estimated that in the initial trials, the time taken to escape was long, but as more trials progressed, the cat would take a few seconds to locate the rope and escape  Not exactly what happened  Thorndike found that the frequency of random behaviours gradually decreased over time  Over several trials, the behaviours that did not lead to escape would occur less frequently, leaving only the correct target behaviour in place  Suggested that animals follow a simple stimulus-type process with little credit for consciousness  Cat seemed to work from a long trial-and-error process of discovery  Thorndike hypothesized a process called Stamping In and Stamping Out o Behaviours like rope pulling were “stamped in” because they lead to rewards o Behaviours like running around in circles were “stamped out” because they led to nothing o Eventually, the general process led to refinement and the cat learned the contingency between the specific behaviour of rope pulling and the specific consequence of food reward  Findings would lead to Law of Effect o Stated that behaviours that produced a satisfying or pleasant state would be stamped in and produced more frequently o Behaviours that produced an annoying or unpleasant effect will be stamped out and performed less frequently Types of Instrumental Conditioning  Four consequences o Presentation of a positive reinforcer (reward) following a response is reward training that increases the behaviour o Presentation of a negative reinforcer (punishment) following a response is punishment training that decreases the behaviour o Omission training  Removing a positive reinforcer following a response, which leads to a decrease in the behaviour being reinforced  Billy is watching TV and teasing his sister  Billy’s mom wants to remove the teasing behaviour, but wants to avoid punishment and its side effects  She turns off the TV every time he teases his sister  Access to the TV show is a positive reinforcer and removing it will likely cause Billy to stop his teasing behaviour o Escape training  Removing a negative reinforcer following a response, which leads to an increase in behaviour  Floor on side of a cage delivers an electric shock every time it is touched  It can be avoided if the rat moves to the opposite side of the cage o Punishment and omission training, although leading to the same decrease in behaviour, are totally different  Four different types of instrumental conditioning differ in whether a positive or negative reinforcer is either presented or removed  An important point for any instrumental conditioning is that it proceeds best when the consequence immediately follows the response Acquisition and Shaping  In instrumental conditioning, process of acquisition leads to learning contingencies between a response and its consequences  Psychologists are often interested in measuring the rate of response of the new behaviour  Autoshaping o Ex. A pigeon is placed in a special cage with a keyhole o If the pigeon pecks at the keyhole, a grain of seed is released o Initially, the pigeon will be unaware of the contingency, but over time the pigeon will peck the keyhole and learn the contingency between the behaviour and the consequence o Can be learned without explicit training by the researched o Simply placing the pigeon in a cage can cause the pigeon to learn the contingency  Shaping by successive approximation o Not all behaviours can be autoshaped o Some are too complex for a subject to discover on their own o Complex behaviour can be organized into smaller steps that gradually build up to the full response we hope to condition o Each of these steps can be reinforced through reward training o Over time, the successive approximation leads to the final complex behaviour o Famous example by behaviourist BF Skinner  Trained two pigeons to play table tennis  Pigeons first learned to peck at the ping pong table to receive food  Once established, the pigeons had to peck at a stationary ball, then a moving ball, then finally peck a ball all the way across a table  As pigeons progressed through these stages, the criteria for rewards became stricter  Chaining o Another procedure used to develop a sequence (chain) of responses to build even more complex behaviours o In chaining, a response is reinforced with the opportunity to perform the next response o Ex. A rat is initially trained to press a lever for a food pellet as the last step in a chain of responses o The next challenge for the rat is an overhanging string placed nearby, the rat must pull the string to gain access to the lever o The response of pulling the string is reinforced by the opportunity to make the original lever press response that leads to food o Step by step, a chain of responses can be built leading to a final sequence of behaviours that can appear to be quite complex Generalization and Discrimination  Discriminative Stimulus o Signals when a contingency between a particular response and reinforcement is “on” o Ex. Whenever a child eats his vegetables in his parents’ house, he is rewarded with dessert o Response (eating vegetables)  reinforcement (dessert) o At his parents’ house, there is a discriminative stimulus (SD) or (S+)  SD  Response  Reinforcement o The environment of his parents’ home becomes an SD for the response of vegetable eating behaviour, which is rewarded with access to dessert o SD  contingency between response and reinforcement is on o However, the child may eat his vegetables at his grandparents’ house and be surprised that he is not rewarded with dessert  This is the Sδ o Sδ is a cue that indicates when the contingent relationship between response and reinforcement is not valid o The environment of the grandparents’ home becomes an Sδ for the response of vegetable eating o The child learns that under these conditions, eating vegetables will not lead to a dessert reward o This behaviour can also be capture on a Generalization Gradient  Recall that not only does a CR happen when a CS is present, it can also happen with similar CS o The child may also expect dessert in environments similar to his parents’ house  Generalization o Consider an example where a girl has learned the contingency between polite behaviour and reward o The presence of the parents is the SD o If she behaves politely when her parents are in the room, she will be rewarded with praise and attention o Little girl might also be polite in front of other adults and authority figures o However, her polite behaviour may not be quite as strong as when her parents are around o As the present figure becomes more different from the original SD, the response of polite behaviour correspondingly decreases  Discrimination and Extinction o Extinction  Let’s say Sarah’s polite behaviour has been diligently rewarded by her parents with praise and attention  During a busy time, they have suddenly stopped paying attention to Sarah and her polite behaviour  This will effectively create an extinction process, which may lead Sarah to stop responding with her polite behaviour o Discrimination  One summer, Sarah is sent on a trip to visit her relatives by herself  Her relatives have never had children and take Sarah’s politeness for granted, without rewarding her  This specific extinction process may lead Sarah to restrict her polite behaviour responses to the presence of the original SD, her parents  SD vs. CS o Classic
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