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PSYC 2210 (13)
Chapter 8

Learning Chapter 8

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York University
PSYC 2210
Anthony Nield

Chapter 8: Stimulus Control of Behaviour → As I pointed out earlier, both Thorndike and Skinner recognized that instrumental responses and reinforcers occur in the presence of particular stimuli. The stimulus control of instrumental behaviour is evident in many aspects of life. Studying, for example, is under strong control of school-related stimuli. The stimulus control of behaviour is an important aspect of how organisms adjust to their environment. The survival of animals (including human animals) depends on their ability to perform responses that are appropriate to their circumstances. Identification And Measurement of Stimulus Control - How can a researcher tell that an instrumental response has come under the control of certain stimuli? Differential Responding and Stimulus Discrimination → Let us look at an experiment by Reynolds, where two pigeons were reinforced on a VI schedule for pecking a circular response key. Reinforcement for pecking was available whenever the response key was illuminated by a visual pattern consisting of a white triangle on a red background. Thus the stimulus on the key had two components: the white triangle and the red color of the background. Reynolds was interested in which of these stimulus components gained control over the pecking behavior. The results showed that one of the pigeons pecked a great deal more when the response key was illuminated with the red light than when it was illuminated with the white triangle. This outcome shows that its pecking behaviour was much more strongly controlled by the red color than by the white triangle. By contrast, the other pigeon pecked a great deal more when the white triangle was projected on the response key than when the key was illuminated by the red light. Thus, for the second bird, the pecking behaviour was more strongly controlled by the triangle. This experiment illustrates several important ideas. First, it shows how to experimentally determine whether instrumental behaviour has come under the control of a particular stimulus The stimulus control of instrumental behaviour is demonstrated by variations in responding (differential responding) related to variation in stimuli. If an organism responds one way in the presence of one stimulus and in a different way in the presence of another stimulus, its behaviour has come under control of those stimuli. Such differential responding was evident in the behaviour of both pigeons Reynolds tested. Differential responding to two stimuli also indicates that the pigeons were treating each stimulus as different from the other. This is called stimulus discrimination. An organism is said to exhibit stimulus discrimination if it responds differently to two or more stimuli. Stimulus discrimination and stimulus control are two ways of considering the same phenomenon. One cannot have one without the other. If an organism does not discriminate between two stimuli, its behaviour is not under control of those cues.Another interestingAspect of reynolds experiment was that pecking behaviour of each bird came under the control of a different stimulus. Reynolds did not direct attention to one of the stimuli at the expense of the other. Therefore, it is not surprising that each bird came to respond to a different aspect of the situation. The experiment is comparable to showing a group of children a picture of a cowboy grooming a horse. Some of the children may focus on the cowboy; others may find the hose more interesting. Stimulus Generalization. → Numerous factors are involved in the identification and differentiation of stimuli. Experimental analysis of the problem have depended mainly on the phenomenon of stimulus generalization. In a sense, stimulus generalization is the opposite of differential responding, or stimulus discrimination. An organism is said to show stimulus generalization if it responds in a similar fashion to two or more stimuli. The phenomenon of stimulus generalization was first observed by Pavlov. He found that after one stimulus was used as a CS, his dogs would also make the conditioned response to other, similar stimuli.Alandmark study of stimulus generalization in instrumental conditioning was by Guttman and Kalish whom first reinforced pigeons on a variable-interval schedule for pecking a response key illuminated by a yellowish- orange light with a wavelength of 580 nanometers (nm). The results showed that the highest rate of pecking occurred in response to the original 580-nm color. But, the birds also made substantial numbers of pecks when lights of 570-nm and 590-nm wavelengths were tested. This indicates that responding generalized to 570 and 590 stimuli. However, as the color of the test stimuli became increasingly different from the color of the original training stimuli, progressively different from the color of the original training stimulus, progressively fewer responses occurred. The results showed a gradient of responding as a as a function of how similar each test stimulus was to the original training stimulus. This is an example of a stimulus generalization. Stimulus Generalization Gradients as Measures of Stimulus Control → With the use of stimulus generalization gradients, investigators can determine exactly how much a stimulus has to be changed to produce a change in behaviour. The wavelength of the 580nm training stimulus had to be changed by more than 10nm before a decrement in performance was observed. This aspect of the stimulus generalization gradient provides precise information about how large a variation in the stimulus is required for the pigeons to respond to the variation. How do you suppose the pigeons would have responded if they had been color blind? In that case they could not have distinguished lights on the basis of color or wavelength. Therefore, they would have responded in much the same way regardless of what color was projected on the response key. Thus, the stimulus generalization gradient would have been flat.A comparison of the results obtained by Guttman and Kalish and our hypothetical experiment with color-blind pigeons indicates that the steepness of a stimulus generalization gradient provides a precise measure of the degree of stimulus control.Asteep generalization gradient indicates good control of behaviour by the stimulus dimension that is tested. In contrast, a flat generalization gradient indicates poor stimulus control. Page 263: Generalization of Treatment Outcomes (Stimulus generalization & behavioural therapy) StimulusAnd Response Factors In Stimulus Control → The central issue in the analysis of the stimulus control is what determines which of the numerous features of a stimulus situation gains control over the instrumental behaviour. In the present section we will consider stimulus and response factors that determine which cues come to control behaviour. Sensory CapacityAnd Orientation → The most obvious variable that determines whether a particular stimulus feature comes to control responding is the organism’s sensory capacity and orientation. Sensory capacity and orientation determine which stimuli are included in an organism’s sensory world. Limitations on the stimuli that can come to control behaviour are also set by whether the individual comes in contact with the stimulus. Consider, for example, a child’s crib. Parents often place mobiles and other decorations on and around the crib to provide interesting stimuli for the child to look at. The mobile consists of several animal figures (a giraffe, a seal, and a lion) made of thin needlework. Which aspects of the mobile in the crib can potentially control the child’s behaviour? To answer this question, one first has to consider what the child sees about the mobile rather than what the mobile looks like to us. From the child’s vantage point under the mobile, only the bottom edges of the animal figures are visible. The shapes of the animals and their surface decorations cannot be seen from below. Therefore, these other features are not likely to gain control of the child’s looking behaviour. Relative Ease of Conditioning Various Stimuli → Having the necessary sense organs and the appropriate sensory orientation does not
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