Transcript quail Buy
What makes effective Conditioned and Unconditioned Stimuli? • Classical conditioning procedures do not always result in learning • Just pairing two stimuli together does not necessarily result in information being stored in the brain, depends on: – timing of stimuli – characteristics of the CS – characteristics of the US Initial responses to the stimuli • Based on Pavlov’s definitions – CS – does not elicit the CR initially (usually biologically weak) – US – elicits the target response without any special training (usually biologically strong) – Need to evaluate responses to determine biological strength • However, a particular stimulus “food” can be a CS or as a US – Food is a special case because • it has several sensory cues, visual, odor, taste • as well as biological consequences, nutrition, toxins and so on – Sucrose food pellets – a tasty treat that rats like • Sucrose food pellets can serve as the CS in a taste-aversion experiment where illness is the US • The same sucrose food pellets could serve as the US in sign tracking – light ---> Sucrose food pellets pairings in a sign tracking procedure – The animal would approach the light The Novelty of Conditioned and Unconditioned Stimuli • The behavioral impact of a stimulus depends on its novelty • Familiar stimuli do not elicit as vigorous a response as do novel stimuli (i.e., Habituation) • Stimulus novelty is also important for classical conditioning • If the CS and/or the US are familiar, conditioning proceeds more slowly than if they were novel (note: can still get conditioning) • Testing the role of stimulus novelty involves 2 phases: – (1) preexposure of the stimulus only – (2) conditioning of CS – US CS-Preexposure effect or Latent Inhibition • Phase 1: Preexposure - Subjects are given repeated presentations of the CS alone – is similar to habituation because the repeated preexposure to the CS limits the processing of, or attention to the stimulus – is due to a stimulus-specific decline of attention – more processing of new inputs and less processing of older unimportant ones – helps preserve limited attentional resources • Phase 2: Conditioning - Subjects are given pairings of the CS with the US – Preexposore of the CS retards learning called “Latent Inhibition” • Recent models of latent inhibition are based on retrieval competition concepts CS-preexposure effect “Latent Inhibition” • Evidence That latent inhibition Is Modulated by Attentional Processes • modulation of latent inhibition by attentional processes that are governed by attentional variables • latent inhibition is reduced by manipulations that maintain or restore attention – a second, neutral, stimulus is paired with the target stimulus on each of its preexposure presentations (masking task) – salience of the stimulus Latent Inhibition Models of Schizophrenia • Latent inhibition measures for Schizophrenia – latent inhibition effects on attentional processes – selective attention disorder, as represented by high distractibility, is central to schizophrenia – nonmedicated acute schizophrenia patients show reduced latent inhibition compared to normal subjects • Nature of Attentional Dysfunction in Schizophrenia – healthy subjects show latent inhibition during the early stages of conditioning – schizophrenics have perseveration of latent inhibition – due to a failure to shift from controlled to automatic processing US-preexposure effect • Experiments on the importance of US novelty are designed in a similar way to CS novelty • Phase 1: Preexposure - Subjects are given repeated presentations of the US alone • Phase 2: Conditioning - Subjects are given pairings of the CS with the US • The initial preexposure to the US usually retards subsequent Conditioning • This may be due to conditioning of background cues during the preexposure phase • Pre-exposure effects have two explanations – Associative Interference - stimuli are less able to form associations – Memory Interference - memory of preexposure interferes with memory of conditioning The Principles of Learning and Behavior, 7e by Michael Domjan Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved. CS and US Intensity and Salience • Stimulus salience – refers to the significance or noticeability of the stimulus – Within limits Learning occurs more rapidly with more salient, or more noticeable stimuli – Intensity increases salience due to greater noticeability – Stimuli relevant to the biological needs of the animal • can increase the salience of a salt taste by depriving the animal of salt • CS Salience – A more intense CS also results in better conditioning • This makes sense from an ecological point of view • a more intense CS will be more salient than the background and will command more attention • With CTA, a stronger concentration of flavor results in bigger taste aversions – using a CS similar to stimuli animals might encounter in the natural environment such as realistic quail models, • see figure 4.2 The Principles of Learning and Behavior, 7e by Michael Domjan Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved. CS-US Relevance, or Belongingness • Rate of Classical Conditioning is also affected by the extent to which the CS is relevant to or belongs with the US – The importance of stimulus relevance was demonstrated in an experiment by Garcia & Koelling (1966) see figure 4.3 and figure 4.4 • They compared learning about peripheral pain (footshock) and learning about nausea type of illness • In nature, rats are likely to get sick after eating poisonous food, but experience peripheral pain after an encounter with a predator • Rats that got poisoned decreased saccharin consumption • Rats that got shocked decreased consumption of the ‘bright and noisy’ water • This experiment suggests that tastes are more readily associated with sickness than with shock (peripheral pain) and that audiovisual cues (LN) are more readily associated with pain/shock than with sickness • We see evidence of this selectivity of association in other species – For example • certain birds locate food by its visual characteristics, rather than by its taste • rats find food mostly by odor • foxes use auditory information The Principles of Learning and Behavior, 7e by Michael Domjan Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved. The Principles of Learning and Behavior, 7e by Michael Domjan Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved. Learning without an Unconditioned Stimulus • In the early research on classical conditioning the US - UR relationship was seen as essential for learning – Some sort of physiological reflex or response system that could be conditioned with a sensory cue the CS – This is OK for many basic examples such as salivary reflex, eyeblink or even nausea from eating bad food • However there are applied situations that are more complex then this where identifying a US - UR relationship may not be possible – Cues in the environment, such as sounds, odors or visual stimuli can be associated with each other. – Wolves may detect an odor, hear a sound and see some movement while searching for food before actually getting contact with the food. Higher-order Conditioning • Historical background – Initially, the CS is weaker than the US – But after conditioning, the CS is strong and elicits a vigorous response – Could the strong CS now serve as a US? • Procedure : See figure 4.5 – A stimulus (CS) that has become strongly conditioned may serve as a US – CS1(tone) - US(food); CS1(tone) -> CR (first-order) – CS2(light) - CS1(tone); CS2(light) -> CR (second-order) – CS3(buzzer) - CS2(light); CS3(buzzer) -> CR (third-order) • Examples – Money is a powerful CS for humans although money is not always closely paired with a US • buy some food and then eat the food later – Crowds can be a powerful fear stimulus (CS) for some people without ever being paired with an aversive US. The Principles of Learning and Behavior, 7e by Michael Domjan Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved. Sensory Preconditioning • Both stimuli elicit weak biological responses before conditioning See figure 4.6 – – – – 1. CS2(light) -> CS1(tone) sequential pairing 2. CS1(tone) -> US(food) -> CR Test: CS2(light) -> CR Note: the Domjan book example of vanilla - cinnamon in food is a confusing example because food can be a US and the flavors are presented simultaneously. • This challenges the concept of differential biological strength • Biological Strength as a facilitator of performance rather than learning • In sensory preconditioning, the initial CS2->CS1 association is “mute” does not produce a response • Making the CS1 biologically strong, allows expression of the association with CS2 • Not all associations are directly evident in behavior CS2 The Principles of Learning and Behavior, 7e by Michael Domjan Copyright © 2015 Wadsworth Publishing, a division of Cengage Learning. All rights reserved.