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Learning Processes

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What is Learning?

Learning is defined as a relatively permanent change in behavior as a result of experience.

A reflex is an immediate response to some stimulus, over which we have little, if any control.

Sensitization refers to an increase in the frequency or amplitude of some response to a stimulus as a consequence of presentation of either that stimulus or, more frequently, some other stimulus

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Conditioning is the basic type of multiple contingency learning. Assuming that higher mental processes are an assemblage of simple conditioned responses, behaviorists tried to study learning in as controlled an environment as possible. Most of the conditioning experiments were done on animals where better control was possible.

As a result of these experiments, they postulated two basic types of conditioning – classical and instrumental.

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Classical Conditioning

An animal is able to detect a stimulus and then to predict what is likely to happen, simply because it has happened several times before. The animal associates two events, which occur together.

If you have pets and you feed them with canned food, what happens when you hit the can opener? Sure, the animals come running even if you are opening a can of green beans. They have associated the sound of opener with their food.

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Classical conditioning was pioneered by a physiologist in the beginning of the twentieth century – Ivan Pavlov (1849 - 1936).

He was a Russian physiologist who was awarded the Nobel Prize for his investigation of glandular and neural factors of digestion.

Pavlov had developed an apparatus, which made it possible to hold and measure the amount of saliva secreted by a dog under various conditions of feeding. A calibrated glass tube was inserted through the dog’s cheek and he was put in a harness in a relatively isolated room with recording devices outside.

Pavlov’s striking discovery was that the animal gave the salivary response even before the sight of food. E.g. he salivated upon seeing the food dish or at the approach of the attendant.

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Paradigm Of Classical Conditioning

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The most famous experiment by Watson is his conditioning of Little Albert. Albert was a small child who was conditioned to fear rabbits because he was again and again presented a rabbit with a loud bang. Eventually, the fear reaction naturally given to the loud bang was also given to the rabbit. Albert also generalized this reaction to all white furry objects, so much so that he also started fearing his mother’s white fur coat even when his mother was wearing it.

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There are four essential elements of the situation in classical conditioning that need description:

US ,The unconditional stimulus is a natural, innate stimulus that reliably elicits a response without prior training. Experimenters do their best to control the past history of the animal to eliminate or control learning that takes place before coming to the laboratory.

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UR ,The unconditional response is the response elicited by the US. Often it is a highly reflexive response, one that happens quickly and automatically whenever the US occurs.

CS ,The conditional stimulus is the neutral stimulus that comes to evoke a response by being paired with the US. It has two essential qualities. Firstly, it must be within the sensory range of the organism, i.e., it must be hearable, seeable, tastable, and so on. Secondly, at the outset of the experiment, it should not produce a response that resembles the UR.

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CR ,The conditional response is the response that arises due to the pairing of the CS and the US.

CR is a preparatory or anticipatory response, whereas the UR is a consummatory response.

the CR is a thought, whereas a UR is a motor response.

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Phenomena in Classical Conditioning

Acquisition – Repeated pairing of the CS and the US increases the strength of the connection until a point is reached where no further observable gain is produced. If the test phase is introduced, it is seen that the CR is given to the CS alone. There are two important determinants of acquisition:

Pairing schedule – The CS and the US may be paired on each trial in a continuous pairing schedule; or they may be paired only on some of the trials in an intermittent schedule. Ross (1959) doing human eyelid conditioning to a light flash found that intermittent schedule reduced the final level of performance to the CS as compared to a continuous pairing. Also more time is taken for acquisition in the intermittent schedule. However, it also requires a greater time for extinction (Hartman and Grant, 1960).

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Temporal relations or time factor – There is an optimum time between the presentation of the CS and the US. If the time between the bell and food is too long or too short, the subject takes too many trials for acquisition. Usually, an interval of 0.5 seconds is used. But the optimum interval depends in the stimuli and responses involved. Garcia and Erwin (1968) showed that rats could learn taste aversion even when the CS – US interval was several hours. Backward conditioning i.e. presentation of food before the bell, generally does not lead to acquisition.

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Extinction – The presentation of the CS without the US results in a progressive decrease in the response. The dog no longer salivates at the sound of the bell if the bell has been rung a number of times without the food being given. The omission of the US is a necessary and sufficient condition for extinction. However, extinction is not a reversal of the acquisition process, resulting in a simple reduction in the strength of association between the CS and the US or the CS and the CR. Phenomena such as spontaneous recovery, external inhibition, and disinhibition led Pavlov and others to the conclusion that extinction occurred due to an distinct inhibitory process in the nervous system.

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Spontaneous recovery – One source of evidence that extinction is not a simple reversal of prior conditioning is the phenomenon of spontaneous recovery. It refers to the recovery of response strength of the CR that takes place after a rest pause during extinction trials. Pavlov found that a rest period of as little as 20 minutes was enough to restore the salivary response to a considerable extent. The longer the delay following extinction, the greater the amount of spontaneous recovery, up to a maximum of about 50% of the response strength after a day’s rest. Even if total extinction has taken place, it does not mean that CR is totally destroyed. If from the next trial, US is again paired with the CS, the animal takes a lesser number of trials for conditioning as compared to the trials taken initially for learning. This is another type of evidence for spontaneous recovery.

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External inhibition – Pavlov’s students often found that after setting up a CR in a dog, they could not show it to Pavlov. This was because the presence of any extraneous stimulus inhibited the conditioned response. Pavlov, being an external factor in the conditioning situation, disrupted the dog’s CR. This phenomenon is called external inhibition.

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Disinhibition – An extraneous stimulus presented during the extinction of a CR tends to reduce the extent of extinction and to restore to some extent the performance of the CR. Pavlov suggested that both external inhibition and disinhibition have a common underlying mechanism because both have the common action of partially reversing or counteracting the ongoing learning process, whether it is acquisition or extinction. However, the nature or existence of this mechanism is far from clear.

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Conditioned inhibition: This phenomenon is of great interest to many psychologists. Originally demonstrated in Pavlov’s laboratory, in one experiment, an automobile horn served as the CS for a salivary CR. After conditioning to the horn had been established, trials were introduced; in which the horn was accompanied by the ticking of a metronome and the food US was withheld. After a number of such trials, the salivary CR decreased to the compound CR, though, the horn CS alone could still evoke salivation. Thus a conditioned inhibitor prevents the performance of the CR. Pavlov also demonstrated that the conditioned inhibitor will function as an inhibitor of the CR even when it is paired with other CS associated with the same CR though it had never itself been paired with any of these CS. In other words it will inhibit the response in any and all situations.

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Stimulus generalization – In the initial phases of conditioning, the organism responds not only to the exact CS but also to a variety of stimuli similar to the CS. However, the response is greatest to the CS and progressively less to the stimulus which is more and more dissimilar to the actual CS. A plot of the strength of CR as a function of distance of the test CS from the original CS is known as the stimulus generalization gradient.

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Discrimination – As conditioning proceeds, the range of stimuli to which the subject responds becomes progressively reduced. After a while, an animal conditioned for 800 megacycles responds only to the stimulus and not to any other frequency of the bell.

Higher order conditioning – Once a CR has been established, the CS may be used instead of the US and may be paired with another CS for the purpose of higher order conditioning. E.g. When the dog has learnt to salivate to the bell, he can be further trained to salivate to a light which is repeatedly paired with the bell. Generally, higher order conditioning beyond the third or the fourth order is difficult to establish in an experimental situation.

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Summation – Two stimuli that have been conditioned separately to the same response tend to evoke a larger response if they are presented together. E.g. If a dog is conditioned separately to light and to bell and if both light and bell are presented together, they evoke a greater salivary response than the response they evoke when presented alone.

Overshadowing – Sometimes, if two stimuli are presented together, one stimulus overshadows the other stimulus due to innate tendencies of the animal i.e. the animal gives a greater response to one stimulus than the other or he is conditioned more easily to one stimulus and not conditioned to the other stimulus. Pavlov himself felt that the salience due to intensity of the stimuli was responsible for overshadowing. Recent researchers however feel that novelty, predictive value of the stimulus or innate tendencies of the organism determine which stimulus will overshadow the other.

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Blocking – Blocking is learnt overshadowing i.e. one CS becomes more important than the other CS because the organism has been initially trained with the first stimulus. Kamin (1969) was the first to demonstrate blocking in the laboratory, arguing that the other blocked stimulus (CS2) never attains stimulus control because it is redundant or irrelevant to the organism.

Sensory preconditioning: When two stimuli CS1 and CS2 are paired before conditioning with CS1 and US takes place with CS2, it is found that the response given to CS1 is also given to CS2. This is evidence for sensory preconditioning. Rizley and Rescorla (1972) point out that sensory preconditioning is far more successful than first order backward conditioning, and that it seems to be restricted to higher order animals, and cannot be demonstrated with lower vertebrate species such as fish and amphibians.

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Configuring – Configuring implies conditioning with a complex CS so that only the total configuration evokes the CR but a small part of the CS does not evoke the CR. There are two procedures to obtain configuring. The first is differential contrasting that involves pairing the compound CS with the US and presenting each component without the US on other trials. The second is prolonged conditioning of the compound CS to the CR without contrasting. Configuring has been demonstrated for both simultaneously present components and successively presented components, though the latter is more difficult. It is also directly related to size and complexity of the brain, higher animals showing more rapid configuring than lower animals, with the general conclusion that fish and amphibians do not configure (Razran, 1971).

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Counter conditioning – This implies substituting the opposite response for the initial response. This frequently happens in the clinical situations. Perhaps the best example is a pioneering experiment by Watson (1912). Initially, Watson used a loud bang as a US and a rabbit as the CS to condition a child to fear a rabbit. After this, Watson did an experiment of counter conditioning in which the same CS was associated with the opposite response of relaxation. Wolpe (1958) uses counter conditioning in his therapy Systematic Desensitization in which the relaxation response is substituted for the anxiety response to various phobic stimuli or anxiety evoking situations.

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Instrumental Conditioning

Instrumental conditioning is the kind of conditioning that allows the organism to act upon and change the environment. According to Gagne (1977) the term instrumental has two advantages: (1) it emphasizes the precise, skilled nature of the responses involved, as in “using instruments” (2) it implies that the learnt connection is instrumental in satisfying some motive. The response is instrumental in attaining the reinforcement.

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instrumental conditioning occurs because the reinforcement is linked to the response.

Instrumental conditioning is also called stimulus response learning or trial and error learning. Skinner’s term for this kind of conditioning is “operant conditioning” emphasizing the fact that the organism has to operate on the environment to get the reinforcement.

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Instrumental conditioning is the process by which many of us train our pets. A dog is rewarded with a biscuit when he stands on his hind legs, and therefore repeats this behavior. However he is punished with the whack of the newspaper on his snout if he tries to climb the bed.

it was Skinner ((1904 – 1995) who explicitly distinguished between respondent behavior and operant behavior and consequently two kinds of conditioning:

Type S conditioning Type R conditioning

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Examples of instrumental conditioning with negative reinforcers are found in the studies of the Yale psychologists – Miller, Mowrer etc. Mowrer’s experiments in 1940s were done in a special apparatus called the shuttle box.

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A shuttle box has two compartments separated by a door that can be dropped partway through a slot in the floor, creating a hurdle over which the dog can jump from the first compartment to the second. Both compartments have grid floors through which current can be passed. To demonstrate instrumental conditioning, the dog is placed in one compartment. At the same time that the door drops he is given a mild electric shock through the grid floor. To escape the shock, the dog jumps over the hurdle to the safety of the second compartment. The door closes and the dog rests until the experimenter drops the door and turns on the shock in the second compartment. The dog must then jump the hurdle again to reach the first compartment, which is now the safe compartment.

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If an apparatus is arranged so that an organism receives an electric shock until it performs a specified response, it will quickly learn to make that response as soon as it is shocked. Such a procedure is called escape conditioning

the response is learned because it is followed by pain reduction.

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With avoidance conditioning, a signal such as light reliably precedes the onset of an aversive stimulus such as an electric shock

With avoidance conditioning, the organism gradually learns to make the appropriate response when the signal light comes on, thus avoiding the shock altogether.

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Reinforcement

Reinforcement is the most important component of operant conditioning. A reinforcer is anything that leads to an increase in the probability of occurrence of the response.

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On basis of Origin

Primary reinforcer: A primary reinforcer is naturally reinforcing to the organism and is related to survival e.g. Food or water.

Secondary reinforcer: A secondary reinforcer is any neutral stimulus, which is associated with the primary reinforcer and thus acquires reinforcing characteristics. Examples are light, sound etc.

Generalized reinforcer: A generalized reinforcer is a secondary reinforcer, which has been paired with more than one primary reinforcer. Its greatest advantage is that it does not depend upon conditions of deprivation to be effective. E.g. money, awards, praise etc.

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On the basis of Effects

Positive reinforcers: A positive reinforcer is something, which increases the probability of the occurrence of the response when it is added to a situation by a response.

Negative reinforcers: A negative reinforcer is something, which when removed from a situation by a certain response increases the probability of occurrence of that response e.g. If a shock is discontinued when the rat jumps over to another box, the response of jumping to the other box increases.

Thus, reinforcement occurs when the response either adds something to the situation (positive reinforcer) or removes something (negative reinforcer). In each case, the probability of occurrence of the response is increased.

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Schedules of Reinforcement

it was Skinner who thoroughly investigated the topic and wrote a book, ‘Schedules of Reinforcement’ in 1957,

The contingencies that can be designed to couple behavior and reinforcement are collectively known as “schedules of reinforcement”.

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Simple schedules are those in which a single type of reinforcement contingency is in force throughout the experimental session.

Compound schedules are combinations of two or more simple schedules in the same experiment.

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Simple Reinforcement Schedules

Continuous reinforcement schedule: Every correct response is reinforced during acquisition. It is usually the basic schedule used to establish the response because it is difficult to bring about acquisition of any response if partial schedules are used during initial training.

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Partial reinforcement schedule: In this case, the response is not reinforced every time it occurs. The reinforcement is given only in some of the responses, not always. It not only leads to a slower acquisition of response but it also leads to slower extinction. The fact that partial reinforcement leads to slower extinction is known as the partial reinforcement effect or Humphreys’ rule after the researcher Humphreys (1939), who first demonstrated it. There are two dimensions upon which the reinforcement may be made contingent – time and behavior. An interval schedule implies that the reinforcement is set up in terms of the time that has elapsed from the delivery of the last reinforcement. A ratio schedule implies that the reinforcement is based on the number of responses emitted by the organism since the last reinforcement.

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Fixed interval schedule: In this case, the organism is reinforced only after a fixed interval of time e.g. A response is reinforced after every 5 minutes. The organism generally learns to anticipate the reinforcement and gives the response only as the interval is about to end.

Fixed ratio schedule: In this case, the number of responses is important E.g. every fifth response may be reinforced. Theoretically, the organism must respond at a very high rate to get the reinforcement. However, as soon as he gets the reinforcement, there is a slight depression in the rate of responding. This is called the post reinforcement pause. Perhaps, this occurs because the organism learns that the responses immediately following a reinforced response are never reinforced.

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Variable interval schedule: In this case, rather than having a fixed time interval, the organism is reinforced on an average of 3 minutes but actually the reinforcement may be given immediately after prior reinforcement or after 30 seconds or 7 minutes or any other time interval. This schedule produces a steady, moderately high response rate.

Variable ratio schedule: In this case, the organism is reinforced on the average of a particular number of responses. E.g. every time responses on an average of 5 will be reinforced. However, practically, it might receive 2 or 3 reinforcements in a row or it may make 10 to 15 responses without being reinforced. This schedule produces the highest rate of responding among all the four schedules.

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Differential reinforcement of low rate: Based on the rate of the response, in this schedule an inter-response time must be equal to or exceed a certain value to secure the reinforcement. For example, a reinforcement may be given only 10 seconds after the previous response. If a response occurs before 10 seconds, the experimenter “resets the clock” and then counts 10 seconds again before giving the reinforcement. Obviously such schedules lead to a very low response rate.

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Differential reinforcement of high rate: In this case high response rates are reinforced. It teaches an organism to consistently perform at a very high rate.

Differential reinforcement of other behavior: this is a unique schedule because it makes the reinforcement contingent on the failure of the response to occur for some specified period. For example, a rat may be given a pellet of food after every 30 seconds if and only if he has not given a response during that period.

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Compound Schedule

Sequential schedules: In this case two or more schedules run one after the other during the experimental session, but only one is in effect at any one time. Reinforcement may be available after one, both, or only after the last component. Some of them are:› Tandem schedules: Here two or more component schedules

must be completed in sequence, before the reinforcement is given. For example: In tand FI 10 FR 20, the animal must respond only after the first 10 seconds, and then give 20 responses before the reinforcement will be given. Such schedules teach us to give a delayed response.

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› Chained schedules: It is similar to tandem schedules, except that a separate discriminative stimulus is associated with each component. In chain FI 10 FR 20, for example, a light may be present in the initial 10 second interval, but absent after that. This schedule is useful to investigate the properties of secondary reinforcers.

› Mixed schedules: Reinforcement is available to the subject in each component, and each of the components may be presented to the subject in alternating order. For example: In mix FI 10 FR 20, the animal must respond only after the first 10 seconds, get the reinforcement, and then give 20 responses before the reinforcement will be given again.The organism comes to know which schedule is operating after experiencing the reinforcement, and quickly learns to match his responses to the schedule in operation.

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› Multiple schedules: It is similar to the mixed schedule, except that a separate discriminative stimulus is associated with each component. In mult FI 10 FR 20, for example, a light may be present in the initial 10 second interval, and a tone may be present after that for the next phase. Again, this schedule is useful to study the properties of secondary reinforcers.

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Simultaneous Schedules

› Alternative schedules: Two or more components run simultaneously, and reinforcement is given when the organism responds to any one of the components. For example: In alt FI 10 FR 20, the animal will get the reinforcement for a response after 10 seconds or after 20 responses, whichever is earlier.

› Conjunctive schedules: Here all components must be completed before reinforcement occurs. For example: In conj FI 10 FR 20, the animal will get the reinforcement after 20 responses and only if at least one response occurs after 10 seconds.

› Concurrent schedules: The component schedules run at the same time, but they are completely independent of each other. They are useful to study choice behavior in organisms.

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Phenomena

Deprivation – The experimental animal is initially put on a deprivation schedule. E.g. If food is to be used as a reinforcer; the animal is deprived of food for 23 hrs prior to the experiment. Skinner does not say that these procedures motivate the animal or produce a drive state. Deprivation is simply a set of procedures, which is related to better measurable performance.

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Magazine training – It implies that the feeder mechanism (also called the magazine) is triggered periodically making sure that the animal is not near the food cup when this happens. Gradually, the animal associates the click of the magazine with the presence of a food pellet.

Lever pressing – Now the animal can be left in the Skinner box on its own. Eventually, it will press the lever, which would trigger the food magazine producing the click that signals to the animal to go to the food cup where it is reinforced by food. According to operant conditioning principles, the lever press response, having been reinforced, will tend to be repeated and when it is repeated, it is again reinforced further increasing its probability of occurrence and so on.

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Shaping – The process of operant conditioning described above takes a long time. There is another approach that can shorten this time period. This is the process of shaping. In this case, the experimenter gives the reinforcement for responses, which bring the organism closer to the desired response. E.g. Initially, he gives reinforcement if the rat is in the half of the Skinner box, which contains the lever. Gradually, he reinforces organism only as he comes closer to the lever. Next, it puts pressure on the lever and finally, only when the animal is actually pressing the lever. This method is also called the method of successive approximation or differential reinforcement. It refers to the fact that only those responses are reinforced which become increasingly similar to the one which the experimenter wants.

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Discriminative operant – After we have conditioned the animal to press the lever, we can make the situation more complex. E.g. we can arrange it so that the animal receives a pellet of food only when the light in the Skinner box is on but not when it is off. Thus, light becomes the discriminative stimulus. In this case, the animal learns to press the lever when the light is on and not to press it when the light is off. Thus, light becomes a signal for the lever press response. We have developed a discriminative operant whereby an operant response is given in one set of circumstances, but not in the other.

Secondary reinforcement – Any neutral stimulus paired with a primary reinforcer also acquires reinforcing properties. It follows that every secondary reinforcer must also be a discriminative stimulus because it is consistently paired with the primary reinforcement. Once established, a secondary reinforcer is independent of the initial response i.e. it not only strengthens that particular response, but also can condition a new unrelated response.

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Generalization – A generalized reinforcer is a secondary reinforcer that has been paired with more than one primary reinforcer. For example: money is a generalized reinforcer because it is associated with many primary reinforcers like food etc.

Extinction – It implies omitting the reinforcement. Skinner holds that this is necessary and sufficient for extinction.

Spontaneous recovery – After extinction, if the animal is returned to his home cage for a period of time and then brought back to the experimental situation, it will again begin to press the lever for a short period of time without any additional training. This is called spontaneous recovery.

External inhibition – If a strong extraneous stimulus such as a tone or light is presented to a rat that is pressing a lever to get food, the response decreases during the presence of the extraneous stimulus.

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Disinhibition – Similar to classical conditioning, stimuli that can produce external inhibition can also produce disinhibition if they are present during extinction. In fact, the more effective external inhibitor is also the more effective disinhibitor (Brimer, 1972).

Conditioned inhibition – The discriminative stimuli present during extinction trials can inhibit any response, whenever they are present. To establish a conditioned inhibitor, the response is not reinforced when it is present, but it is reinforced when it is absent.

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Superstitious behavior – If the organism is reinforced periodically regardless of what it is doing, it acquires strange ritualistic responses. E.g. It may run in circles, stand up on its back legs or bob his head i.e. it performs the actions, which were reinforced by the experimenter accidentally. This behavior is similar to superstitious behavior in humans.

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Chaining – One response can bring the organism into contact with stimuli that act as a discriminative stimulus for another response, which in turn causes it to experience stimuli that lead to a third response and so on. This process is called chaining. In fact, most behaviors involve some form of chaining. The stimuli in the Skinner box cause the animal to turn towards the lever; the sight of the lever causes him to approach it and then to press it. The firing of the food magazine is an additional stimulus, which elicits the response of going to the food cup. Consuming the food pellet is another stimulus to the animal to return to the lever and again press to it. This sequence of events is a chain held together by the food pellet that is the primary reinforcer. It can be said that the various elements of the chain are held together by secondary reinforcers, but the entire chain depends in the primary reinforcer. If the primary reinforcement is withdrawn, the chain breaks down. It is also important to realize that the chain is developed backwards from the primary reinforcer. Animals have been trained to perform complex responses with the help of this principle. E.g. Skinner trained a rat to climb a staircase, ride a cart, cross a bridge play a note on a toy piano, enter a small elevator, pull a chain, ride the elevator down and press a lever to get the pellets of food.