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Lecture 4+5 Classical Conditioning.docx

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McMaster University
Joe Kim

Psychology Lecture 4/5: Classical Conditioning Bernard Ho September 25, 2010 Orienting Responses, Habituation and Sensitization  Orienting responses are important for focusing your attention to evaluate unfamiliar stimuli which may potentially signal danger or unexpected opportunity  However, if you responded equally to every stimuli in the environment, you would become overwhelmed and your divided attention may cause you to miss out on critical information  Habituation o A simple form of learning shown by a decrease in response to a stimuli or event as it becomes familiar o Functions to limit an orienting response and to ignore inputs that have become familiar and found to be inconsequential o In some situations, the opposite effect to habituation is just as important o Two processes can lead to an increase in responsiveness to a stimulus or event o Dishabituation is an increase in responding that follows a change in the stimulus that has become familiar  Is important because a change in stimulation of a familiar stimulus can indicate important information  The other process is sensitization o Increase in response to repeated presentation o Can be an adaptive behaviour because it prompts you to engage in behaviours appropriate to escaping a potentially harmful stimulus  Key difference between the two processes is that dishabituation involves the recovery of the original response, while sensitization produces a response stronger than the original one  Whether a particular stimulus leads to habituation or sensitization depends on factors such as intensity of the stimulus o More intense stimulus tend to lead to sensitization and modestly intense stimuli tend to lead to habituation Learning  Refers to a relatively enduring change in an organism’s behaviour, capabilities or knowledge due to experience  Two types o Classical conditioning  Allows us to associate two related events  The learning of a contingency between a particular signal and a later event that are paired in time/space  Cue (signal) + event  reaction  Cue (signal)  reaction  Ivan Pavlov  Sound of a metronome signalled to a dog that food was about to be delivered  Prior to training, sound of metronome had no observable effect on dog’s behaviour  After training, a dog would begin to salivate in response to sound of metronome alone  New behaviour was called conditional reflex  Pavlov was technically studying a contigent relationship, presentation of one stimulus reliably leads to the presentation of another  Ex. Flash of lightning before crash of thunder  When an organism learns the association between a signal and an event, a contingency has formed between the two stimuli  Learning these contingencies is the essence of classical conditioning  Conditional response can promote survival o Instrumental conditioning  Allows us to associate actions and consequences Terminology  Unconditional stimulus o One that unconditionally, naturally and automatically triggers a response in the absence of learning o Food placed in dog’s mouth  Unconditional response o Specific response that unconditional stimulus naturally triggers o Biologically determined reflex that is elicited in the absence of prior learning o When US occurs, UR always follows without any need for training o Salivation after food placed in dog’s mouth  Conditional stimulus o Previously neutral stimulus, that after becoming associated with the US, eventually triggers a response of its own o Sound of metronome with food placed in dog’s mouth o Typically appears before the US  Conditional response o Following pairing with US, CS elicits a conditioned response o Often CR is very much like UR o CS of sound of metronome will eventually elicit a CR of salivation  Acquisition o Process by which a contingency between a CS and US is learned o Pavlov characterized the process of acquisition as following a negatively accelerating curve o Most learning happens in early trials o During each additional trial, there is some learning, but never as much as in the earlier trials o Taste aversion  Ex. When rats eat something bad for them, they won’t eat anything else similar to it  Atypical because happens after one trial Extinction  Lasting effects o In theory, as long as the CS continues to be a reliable cue for the US, contingency will be maintained o However, if conditions change such that the CS is no longer a reliable cue for the US, the CR will eventually fade  Extinction is the process in which a CR can be made to fade o Involves presenting the CS alone (without US) repeatedly over many trials o At first, CS will elicit the CR, but eventually CR will become weaker and weaker, until it fades  Learning perspective o Two hypotheses  Is previous contingency unlearned?  If so, retraining between CS and US would lead to acquisition of the CR at same rate as original training  Old learned contingency remains and competes with new inhibitory response that is learned to the CS?  If so, retraining between CS and US would occur at a faster rate compared to original training  Spontaneous recovery o Suggests that extinction involves a new inhibitory learned response o Following an extinction period in which CS is presented repeatedly in absence of US, CR gradually fades o However, following a rest period, the CS is presented again and it elicits the CR o Suggests that extinction seems to promote a learned inhibitory response that competes with original learned contingency o One possible explanation is the phenomenon of renewal  If a response is extinguished in a different environment than where it was acquired, the fully expressed CR is observed if the animal is returned to the environment in which acquisition took place  Furthermore, reconditioning proceeds faster than initial acquisition o In other words, relearning is faster than the original rate of learning o Even following extinction in which the CR is no longer observed the subject still retains some memory of the learning Higher Order Conditioning  In higher order conditioning, the established CS is now paired with a new stimulus, creating another CS capable of eliciting a CR  Typically, the CR elicited in HOC is weaker and more vulnerable to extinction compared to the original CR  Despite these limitations, HOC greatly expands the power and influence of associative learning  Ex. Children have a fear of being injected with a needle at the doctor’s office  Just the sight of the needle (CS) causes them to experience fear  In time, many associated stimuli (sight of doctor’s office, the word “doctor”) can elicit the fear response Generalization and Discrimination  Stimulus generalization o Process where classical conditioning of learned responses to a variety of different stimuli occurs o During training, one specific CS may be paired with a US to produce a contingency o However, stimuli similar to the CS will often also produce a CR  Generalization Gradient o In a fear conditioning experiment, a 500 Hz tone CS is paired with a mild electric shock o As training proceeds, eventually the presentation of the 500 Hz tone CS alone will lead to a fear conditioned response o Once contingency between tone CS and shock US has been established, we can test for stimulus generalization by presenting various tones and measuring the fear CR o As the fear response CR is plotted against various tones, a normal distribution appears, called a generalization gradient o Strongest CR is elicited by the original 500 Hz CS o Tones similar to the CS elicit similar fear levels o However, as you test with higher or lower frequency, progressively less and less fear is elicited  In this way, stimulus generalization adds flexibility and efficiency to classical conditioning o If a US is potentially harmful, you will not require separate conditioning experiences to learn that relationship instead, you will generalize your learning to avoid similar CSs that cue potential danger  During extinction training, subject is exposed to the training CS in the absence of the US  Now, if we test a variety of CSs to construct a generalization gradient, our data fits a separate gradient as the one before the training  In the new gradient, the strength of the CR is flattened along the original gradient  Largest loss in strength of CR is for the original CS  However, generalized CR for non-training stimuli is also diminished  Discrimination Training o While stimulus generalization allows a variety of CSs to elicit a CR to some degree, stimulus discrimination does the opposite o It restricts the range of CSs that can elicit a CR o Suppose as a child, a black Doberman bit you o
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