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Chapter 4

Chapter 4. Supplemental Material. Salience. The general perceived strength of stimuli It refers to the intensity of the subjective experience of stimuli, not of the objective intensity of the stimuli themselves Salience, as subjective experience, varies b/w individuals and b/w species

breanna-velazquez
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Chapter 4

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  1. Chapter 4 Supplemental Material

  2. Salience • The general perceived strength of stimuli • It refers to the intensity of the subjective experience of stimuli, not of the objective intensity of the stimuli themselves • Salience, as subjective experience, varies b/w individuals and b/w species • It depends on some combination of physical characteristics of stimuli and of the sensory system of the perceiver

  3. Overshadowing • 1st Training2nd TrainingTest US alone CS1-CS2 & US CS1 alone CS2 alone • In this experiment, 1st, the US is presented alone • 2nd, two CSs, CS1 and CS2, are presented together • Lastly, measure the strength of the conditioning to the stimuli presented individually

  4. Results of Overshadowing Experiment • What occurs is that the strength of the conditioning to each CS ends up depending on the intensity of the CS • e.g., if CS1 is a dim light and CS2 is a bright light, then after conditioning to the CS1-CS2 combination, the CR to the bright light is very strong while the dim light produces little or no reaction • The perceived strength of the stimuli is what is referred to as their salience • The more salient stimulus overshadows the less salient stimulus

  5. Blocking Experiment • 1st Training2nd TrainingTest CS1-US CS1-CS2 & US CS1 alone CS2 alone • 1st, present stimulus 1 with the US • 2nd, present stimulus 1 and 2 at the same time with the US • 3rd, measure strength of conditioning to stimulus 1 and stimulus 2 independetly

  6. Results of Blocking Experiment • When the stimuli are tested individually, the animal will show strong conditioning to Stimulus 1 and little or no conditioning to Stimulus 2 • This is because the prior pairing of the first stimulus with the US stops the US (i.e., blocks it) from being associated with other stimuli presented later

  7. Summary • Overshadowing: with no prior pairings of CS1 and CS2, the stimulus with the greatest salience (e.g., the brightest light) will be conditioned to the US • Blocking: Out of two stimuli, the stimulus initially presented with the US will block the second stimulus from being conditioned to that same US

  8. Rescorla & Wagner’s Model of Classical Conditionig • According to Rescorla and Kamin, associations are only learned when a surprising event accompanies a CS • In a normal simple conditioning experiment, the US is surprising the first few times it is experienced so it is associated with salient stimuli which immediately precede it • In a blocking experiment, once the association b/w the CS (CS1) presented in the 1st phase of the procedure and the US has been made the US is no longer surprising (since it is predicted by the CS1)

  9. Rescorla & Wagner Cont. • In the 2nd phase, where both CS1 and CS2 are experienced, since the US is no longer surprising it does not induce any further learning – therefore, no association is made between the US and CS2 • This explanation was presented by Rescorla and Wagner (1972) as a formal model of conditioning which expresses the capacity a CS has to become associated with a US at any given time

  10. Cont. • The associative strength of the US to the CS is referred to by the letter V and the change in this strength which occurs on each trial of conditioning is called dV • The more a CS is associated with a US, the less additional association the US can induce • dV = ab(L – V) • Where a = the salience of the US • b = the salience of the CS • L = the amount of processing given to a completely unpredicted US

  11. Cont. • When the US is first encountered, the CS has no association to it so V = 0 • On the first trial, the CS gains a strength of abL in its association with the US, which is proportional to the saliences of the CS and the US and to the initial amount of processing given to the US • As trial 2 is started, the associative strength V is abL so the change in strength that occurs with the second pairing of the CS and the US is • ab(L – abL)

  12. Cont. • It is smaller than the amount learned on the 1st trial • This reduction in amount that is learned reflects the fact that the CS now has some association with the US, so the US is less surprising • As more trials occur, the equation predicts a gradually decreasing rate of learning

  13. References • The material presented was adapted from a lecture provided by R. W. Kentridge • It can be found on the following website: http://brembs.net/classical

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