Chapter 10: Generalization, Discrimination, and Stimulus Control Flashcards
(21 cards)
What is generalization? Why is generalization such an important topic? Describe response generalization and stimulus generalization. (pp. 314–315)
Generalization is the tendency for the effects of a learning experience to spread.
Response generalization is the tendency for changes in one behavior to spread to other behaviors. If a rat receives food after pressing a lever with its right front foot, it might then press the lever with its left front foot, or with its chin. Similarly, if a child is rewarded for expressing a willingness to share a toy, she is then more likely to actually share a toy.
Stimulus generalization is the tendency for changes in behavior in one situation to spread to other situations.
What is a generalization gradient? Provide and recognize original examples of generalization gradients. Describe Guttman and Kalish’s study of stimulus generalization in pigeons. (pp. 315–316)
GENERALIZATION GRADIENT - PLOTTED DATA OF STIMULUS GENERALIZATION
Carl Hovland (1937) studied the generalization of fear conditioning in college students. He began by pairing a tone of a particular pitch with a mild electric shock; the UR was the galvanic skin response, or GSR (a measure of emotional arousal). After 16 pairings of the CS and US, Hovland then presented four tones, including the CS. The results showed that the GSR spread from the original tone to the others; the less a stimulus resembled the CS, the weaker the CR was. When data on stimulus generalization are plotted on a graph, they yield a figure called a generalization gradient.
In a classic study, Norman Guttman and Harry Kalish (1956) trained pigeons to peck a disc of a particular color and later gave them the opportunity to peck the disc when it was various colors, including the color used in training, for 30 seconds each. Pigeons pecked the disc most frequently when it was the color used during training, but they also pecked the disc when it was other colors. As the generalization gradient reveals, the more closely the disc resembled the training disc, the more often the birds pecked it.
Can generalization of the effects of extinction and punishment occur? Describe Honig and Slivka’s (1964) study of inhibitory stimulus generalization. (pp. 316–317)
Studies of generalization usually involve the effects of reinforcement, but changes in behavior produced by extinction also spread beyond the learning situation. For example, R. E. P. Youtz (reported in Skinner, 1938) trained rats to press a horizontal lever for food and then put the behavior on extinction. After this, he tested the rats in a chamber with a vertical lever. He found that the effects of the extinction procedure reduced the rats’ tendency to press the new lever.
The suppression of behavior produced by punishment spreads in much the same way as the effects of reinforcement and extinction. Werner Honig and Robert Slivka (1964) trained pigeons to peck discs of various colors. When the birds were pecking all the colors at the same rate, the experimenters continued reinforcing disc pecks but also punished pecking whenever the disc was a particular color. The tendency to peck the disc when it was that color declined, of course, but so did the tendency to peck when the disc was other colors. The frequency of pecking varied systematically with the similarity of the disc to the punished color.
In what way have researchers identified strategies to increase generalization? (p. 318)
One way is to provide training in a wide variety of settings. If you want a pigeon to peck discs no matter what their color, reinforce disc pecking of a wide variety of colors. A related idea is to provide lots of examples. Another tactic is to vary the consequences. If you are reinforcing a behavior, vary the kind, amount, and schedule of reinforcers. Another tactic is to reinforce generalization when it occurs.
Provide and recognize original examples of cases in which generalization is not helpful. Describe Dweck and Repucci’s (1973) study illustrating this aspect of generalization. (pp. 318–319)
A behavior that is useful in one situation is not always helpful in another. Thorndike (1898) noticed, for example, that a cat that had learned to escape from a box by pulling on a loop would later paw at the same spot—even though the loop had been removed! In the same way, a college student whose off-color jokes get big laughs in the dormitory may find that the same jokes are not appreciated at the family dinner table.
Carol Dweck and Dickon Repucci (1973) showed how generalization can work against a teacher and her students. Teachers first gave students unsolvable problems. Later these teachers gave the students problems that could be solved, but the students failed to solve them. The tendency to give up seems to have generalized from the first situation to the second.
How have therapists improved clients’ behaviour away from clinics? Is this easily achievable? (p. 320)
The problem of generalization is critical for therapists: there is little value in changing behavior in a hospital or clinic if those changes do not carry over to the home and workplace. One way to attack the problem of generalization is to try to alter the natural environment so that appropriate behavior continues to be reinforced at a high rate.
What is discrimination? Provide and recognize original examples of discrimination. Explain how discrimination and generalization are inversely related. (pp. 320–321)
Stimulus discrimination is the tendency for behavior to occur in certain situations but not in others.
You can see that discrimination and generalization are inversely related: The more discrimination, the less generalization, and vice versa.
What are discriminative stimuli? What symbols are used to designate different types of discriminative stimuli? (pp. 321–322)
In operant discrimination training, one stimulus, designated S+ or SD typically indicates that a behavior will have reinforcing con- sequences, and another stimulus, S− or S∆ indicates that the behavior will not have reinforcing consequences. SD and S∆ (ess-dee and ess-delta) are both discriminative stimuli—that is, stimuli that signal different consequences for a behavior.
Define successive and simultaneous forms of stimulus discrimination training. Provide and recognize original examples of each type. (pp. 322–323)
In simultaneous discrimination training, the discriminative stimuli are presented at the same time.
In successive discrimination training, the SD and S∆ alternate, usually randomly. When the SD appears, the behavior is reinforced; when the S∆ appears, the behavior is not reinforced.
What is a matching to sample procedure? Provide and recognize original examples of matching to sample. (p. 323)
In a procedure called matching to sample (MTS), the task is to select from two or more alternatives (called comparison stimuli) the stimulus that matches a standard (the sample). The comparison stimuli include the SD —the stimulus that matches the sample—and one or more S∆.
What is an oddity matching procedure? Provide and recognize original examples of oddity matching. (p. 324)
The example of MTS just given is very simple, but the procedure can be more complicated. For example, a bird may be required to peck a disc that is different from the sample, a variation of MTS called oddity matching or mismatching.
What is errorless discrimination training? Provide and recognize original examples of such training. (pp. 324–325)
Herbert Terrace found that errors can be reduced through errorless discrimination training. In this procedure the S∆ is presented in very weak form and for short periods. For example, in training a pigeon to discriminate between a red disc (the SD) and a green disc (the S∆), Terrace (1963a) presented the red disc at full strength for three minutes at a time, but presented an unlit green disc for only five seconds.
What is the Differential Outcomes Effect (DOE)? Provide and recognize original examples of this effect. (pp. 325–327)
Another way to improve the rate of discrimination learning is to vary the consequences. In an experiment by M. A. Trapold (1970), rats could press either of two levers. When a light came on, pressing the lever on the left was reinforced, but when a tone sounded, pressing the lever on the right paid off. However, in this experiment Trapold provided different consequences for the two responses. The reinforcer for pressing on the left lever was food; the reinforcer for pressing on the right lever was sugar water. The result was that the rats learned to make the appropriate discrimination more quickly and achieved a higher level of accuracy than when reinforcers were the same for each response. This finding—improved performance in discrimination training as a result of different consequences—is called the differential outcomes effect (DOE).
Discuss the important practical applications of the differential outcomes effect (DOE)? (p. 327)
Discrimination learning is not merely an interesting laboratory phenomenon; it has important practical applications. Learning a second language in adulthood can be difficult because of differences in the sounds of the two languages. To the Japanese, for example, the English L sounds like the Japanese R. James McClelland, Julia Fiez, and Bruce McCandliss (2002) provided discrimination training to Japanese adults living in the United States. Training consisted of listening to an audiotape and indicating which of two words, one starting with L, the other with R, they heard. For some participants the two words were rock and lock; for others the words were road and load. Some participants got immediate feedback after each effort; others did not. The training consisted of only three 20-minute sessions, yet the participants showed marked improvement. (Those who did not get feedback showed far less progress.)
Discrimination training has also proved useful in training animals to help humans with a variety of tasks. For a dog to sniff out illegal drugs, for instance, requires discriminating among various fragrances. Animals with a keen sense of smell can also locate landmines.
Define stimulus control. Provide and recognize original examples of stimulus control. (pp. 328–329)
Consider a rat that has learned to press a lever when a light is on but not when the light is off. In a sense, you can control the rat’s lever pressing with the light switch: Turn it on, and the rat presses the lever; turn it off, and the pressing stops. When discrimination training brings behavior under the influence of discriminative stimuli, the behavior is said to be under stimulus control.
Rats are not the only creatures, of course, that have behavior under stimulus control. While you are driving, if you approach an intersection and the traffic light turns red, you move your foot to the brake pedal. When the light turns green, you move your foot to the gas pedal. Your behavior has, as the result of discrimination training, come under the influence of the traffic signal. Similarly, you tend to enter stores that have signs that say “Open” and walk past stores that are marked “Closed.”
When a discrimination has been well established, the behavior is said to be under stimulus control. Generally that means that the behavior is orderly and efficient, that it enables us to obtain desirable consequences and avoid undesirable ones. Stimulus control can work against us, but we can also use it to our advantage.
Describe the research of Reit et al. (1996) on mental rotation. Why does the term mental rotation not explain the participant’s responses in these experiments? (pp. 329–330)
Donna Reit and Brady Phelps (1996) used a computer program to train college students to discriminate between geometric shapes that did and did not match a sample. The items were rotated from the sample position by 0, 60, 120, 180, 240, or 300 degrees. The students received feed- back after each trial. When the researchers plotted the data for reaction times, the results formed a fairly typical generalization gradient.
These data clearly suggest that “mental rotation” data are generalization data.
What is a concept? What does it mean to understand a concept? (p. 331)
The word concept usually refers to any class the members of which share one or more defining features. The defining features allow us to discriminate the members of one class from the members of another.
A concept is not a thing, however, but, as Fred Keller and William Schoenfeld (1950) put it, “only a name for a kind of behavior.” They explain: “Strictly speaking, one does not have a concept, just as one does not have extinction—rather, one demonstrates conceptual behavior by acting in a certain way” (p. 154). Concepts require both generalization and discrimination. One must generalize within the conceptual class and discriminate between that and other classes. So, for example, to understand the concept, spider, one must both recognize a variety of spiders when one sees them, including spiders one has never seen before, and distinguish between spiders and other critters, such as ants and aphids. As Keller and Schoenfeld put it, “Generalization within classes and discrimination between classes—this is the essence of concepts.”
Can animals learn complex concepts through discrimination training? Comment on the research of Herrnstein et al. (1964). (p. 332)
Richard Herrnstein and his colleagues performed a series of brilliant experiments aimed at answering this question. In the first of these, Herrnstein and D. H. Loveland (1964) projected photographic images within a pigeon’s chamber. The images included countryside, cities, bodies of water, lawn, meadow, and so on. About half of the photographs included at least one per- son, while the others did not. If the bird pecked a disc when an image included a person, it received food; if it pecked when there was no person, it received nothing. The people in the photos were sometimes partly hidden by other objects. Sometimes there was one person, sometimes a group of people. Some of the humans were clothed, some partly clothed, some nude. They included males and females, adults and children, and people of different races. Thus, to get food for pecking, the birds had to respond to a wide variety of human images. Any normally functioning adult could easily perform the task, but could a pigeon? The answer was a clear, Yes.
Describe smoking and quitting smoking in terms of stimulus control relationships. How can you use stimulus control principles to make it more likely that someone will quit smoking successfully? (pp. 334–336)
“Drug-associated stimuli” include environmental events that, because they have preceded tobacco use in the past, have acquired some degree of stimulus control over tobacco use. In other words, drug abuse, including smoking, is under stimulus control.
The research on the role of stimulus control in smoking has important implications for those who would like to quit. It would appear that there are two basic approaches to preventing relapse. The former smoker can avoid situations in which he or she often smoked in the past, thereby avoiding the ability of these situations to elicit smoking. Or the smoker can undergo training to reduce the control these situations have over his or her behavior. It is extremely difficult, if not impossible, for a smoker to avoid all situations in which he or she has smoked; therefore, the best bet may be to undergo training that will undermine the power of those situations. This might be done, for example, by gradually exposing the smoker to those situations while preventing him or her from smoking.
Describe the research of Wansinck (2006) that demonstrates the power of environmental cues in eating. (p. 336)
Brian Wansink (2006), a marketing professor at Cornell University, talks about the effects of “hidden persuaders,” environmental cues for eating. He describes an experiment in which people ate soup from a bowl that automatically refilled as they ate. Normally an empty soup bowl is a cue to stop eating, but in this case there was no such cue. People tended to eat more than one bowl of soup, but some people ate much more—in some cases, more than a quart of soup. If an empty bowl or an empty plate is a discriminative stimulus to stop eating, then limiting the amount of food we serve ourselves can help reduce calorie consumption.
Describe the following theories of stimulus discrimination/generalization: (a) Pavlov’s theory, (b) Spence’s Theory, (c) the Lashley-Wade theory. What are the main criticisms of these theories? Has any of these theories won universal support? (pp. 336–341)
Pavlov’s theory is physiological. He believed that discrimination training produces physiological changes in the brain. Specifically, it establishes an area of excitation associated with the CS+ and an area of inhibition associated with the CS−. If a novel stimulus is similar to the CS+, it will excite an area of the brain near the CS+ area. The excitation will irradiate to the CS+ area and elicit the CR. Similarly, if a novel stimulus resembles the CS−, it will excite an area of the brain near the CS− area. The excitation of this area will irradiate to the CS− area and inhibit the CR. Pavlov’s theory provides an intuitively appealing explanation and, wrapped as it is in physiology, it has the smell of science. Unfortunately, the physio- logical events were merely inferred from observed behavior. Pavlov presumed that irradiation of excitation occurred because generalization occurred, but there was no independent validation of its happening. The theory therefore suffered from circularity.
Spence’s theory of generalization and discrimination. CS+ training produces a gradient of excitation; CS– training produces a gradient of inhibition. The tendency to respond to a stimulus near the CS+ is reduced to the extent that it resembles the CS–. The tendency not to respond to a stimulus near the CS– is reduced to the extent that it resembles the CS+. What Spence proposed was that the tendency to respond to a novel stimulus following discrimination training would be equal to the net difference between the excitatory and inhibitory tendencies. In other words, the tendency to respond to a novel stimulus will be reduced by the tendency not to respond to that stimulus. Consider a hypothetical experiment in which a pigeon is trained to peck an orange disc but not a red one. After training, we give the bird the opportunity to peck the disc when it is a variety of colors, from pale yellow to deep red. What color disc will it peck most often? We know that if the bird had merely received food for pecking the orange disc, it would peck that same color most often. But discrimination training, according to Spence, should result in inhibition of the tendency to peck stimuli resembling the S∆. Spence’s theory therefore predicts that the peak of responding will not occur at the SD but at a stimulus further away from the S∆. In other words, the peak of responding will not be on the orange disc but on one that is even less reddish.
Karl Lashley and M. Wade (1946) proposed an approach to generalization and discrimination that differs from those of Pavlov and Spence. These researchers argued that generalization gradients depend on prior experience with stimuli similar to those used in testing. Discrimination training increases the steepness of the generalization gradient because it teaches the animal to tell the difference between the SD and other stimuli. But the generalization gradient is not usually flat even in the absence of training. Why is this so if the gradient depends on training? The answer Lashley and Wade give is that the animal has undergone a kind of discrimination training in the course of its everyday life. A pigeon, for example, learns to discriminate colors long before a researcher trains it to peck a red disc. The more experience a pigeon has had with colors, especially those resembling the SD, the steeper its generalization gradient will be; the less experience the bird has had, the flatter the gradient will be. The theory implies that if an animal is prevented from having any experience with a certain kind of stimulus, such as color, its behavior following training will be affected. If such a color-naïve animal is trained to respond in the presence of a red disc, for example, it will later respond just as frequently to a green disc. In other words, its gradient of generalization will be flat. Not all tests of the Lashley–Wade theory have yielded positive results, but it is now generally acknowledged that the steepness of a generalization gradient depends to some extent on the experience the participant has had with the relevant stimuli before training.
