Pavlov also found that the dog that had been conditioned to salivate to the sound of the tone would also salivate to a similar sound such as a metronome or buzzer. It seemed that any stimulus similar in characteristics to the conditioned stimulus would also elicit the conditioned response; this phenomenon is known as stimulus generalization. A general rule of this phenomenon is the bigger the difference between the new stimulus and the original CS, the weaker the CR will be. This can be beneficial to animals, as it is useful for us to have the ability to transfer our learning from one situation to another, so we do not spend all our time learning. Although it could be dangerous for us to generalise all that we learn, for example if we did not learn to discriminate between the red and green lights at traffic lights the consequences could be fatal (Lang & Teahan 2001). We must therefore learn to discriminate which involves learning to make one response to a stimulus and no response or a different response, to a different but similar stimulus. The phenomenon of discrimination was shown quite clearly in Pavlov’s dog experiments, even though to begin with the dogs salivated in response to similar sounds to the tone (generalisation) they soon learned to discriminate between them and only salivated in response to the conditioned stimulus which the food was paired with.
Pavlov also demonstrated that a conditioned response can be undone using a very similar technique as the one used to establish it to begin with. He found that if the conditioned stimulus (CS) continued to be presented but now alone without the unconditioned stimulus, then the conditioned response would gradually weaken and finally would disappear. This phenomenon Pavlov called extinction. If the tone was not sounded as the food was presented for several trials the dog soon learned not to salivate simply to the sound of the tone. This may resemble forgetting but actually enables an animal to adapt and respond to changes in its environment, however after extinction the animal will never return to its ‘original’ naive state it will always retain the memory of what it has learnt. This is demonstrated by a phenomenon called spontaneous recovery, which supports the idea that extinction is not forgetting. When an animal has undergone extinction, therefore has stopped responding to the CS, and is then given a rest interval away from the experimental situation, but is then returned to it and the CS is presented again it will often elicit the CR, which had been fully extinguished. In the case of Pavlov’s dogs salivation to the tone had been completely extinguished (extinction), however after a rest period they would salivate in response to the conditioned stimulus (CS). The response seemed to have recovered spontaneously without any need for further pairing of the CS and UCS.
It is thought that the animal remembers that the tone had been informative in the past, so when it is placed back in the experimental situation it checks to see if the tone will again be informative, this produced the phenomenon known as spontaneous recovery (Robbins, 1990 citied in Gleitman 1999).
The other main behaviourist approach is instrumental or operant conditioning, this also involves many of the main phenomena of learning that are present in classical conditioning. Instrumental conditioning focuses more on the consequences of behaviour, an animal’s actions has consequences, and it is these consequences that determine how likely that response is to be repeated. Thorndike (1913) found that learning may occur without any associations between two stimuli (Cardwell et al 2001). He developed a series of experiments in which hungry cats had to find their way out of puzzle boxes. He described the process involved as trial and error learning where the responses that are reinforced are ‘stamped in’ by the positive result and are likely to be repeated. The cats could only escape by pressing a lever, before learning the correct strategy the cats tried other behaviours such as scratching, biting and howling, all of which were unsuccessful. However when the cat accidentally presses the lever whilst exploring its environment it is then able to escape. This reinforces the action of pressing the lever because it is followed by a beneficial consequence. When the cat is placed back in the box it took less and less time for it to produce the response that unlocked the door (pressing lever) eventually pressing the lever becomes the main focus of the cat’s behaviour. (Cardwell et al 2001). This period when learning takes place is again called the acquisition period as in classical conditioning.
Although Thorndike began the experimental study into instrumental conditioning B. F. Skinner is the name most widely linked to the subject. Skinner referred to instrumental conditioning as operant conditioning because animals operate on their environment to bring about change that leads to rewards. Skinner supported Thorndike’s idea of ‘the law of effect’, which states that the consequence of a behaviour will act as to either strengthen or weaken that behaviour (Gleitman et al 2001). Skinner developed an experiment where an instrumental response could be performed continuously and rapidly, he designed an experimental chamber known as the ‘Skinner box’. The Skinner box contained a lever which a rat can press or a lighted disc at which a pigeon could peck. It also contained a food tray into which a pellet of food could be delivered as reinforcement for pressing the lever or pecking the light. Pecking the light for the pigeons and pressing the lever for the rats are the learned responses: the operant responses. If the stimulus is continued to be presented and the animal shows the desired behaviour but does not receive the beneficial consequence or reinforcement extinction will eventually occur. The rate at which extinction occurs in operant conditioning depends upon the schedule of reinforcement, if the animal is only partially reinforced extinction takes longer to occur (Staddon & Ettinger 1989). As in classical conditioning spontaneous recovery is also present when the stimulus is presented again after the animal has had a rest period.
Generalization and discrimination also function quite similarly in classical and instrumental conditioning. Pigeons were originally reinforced when they pecked at a yellow light. When the pigeons were tested with lights of varying colours they showed a standard generalization gradient. This meant they pecked more often at the colours that were most similar to original stimulus yellow, such as orange and green rather than colours such as blue and purple (Gleitman et al 1999). The pigeons however soon learned to discriminate between the similar colours when they did not receive a reward (food) for pecking when the orange and green lights were shown.
It is clear that there are central phenomena of learning that are common to both classical and instrumental conditioning. Both types of learning are based on association and reinforcement, but they do differ in some aspects. In classical conditioning the reinforcement comes before the conditioned response, and in instrumental conditioning the animal must first show the conditioned response before they receive the reward.
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REFERENCES
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Cardwell, M., Clark, L. & Meldrum, C. (2001) Psychology for A2 Level. London. HarperCollins Publishers Ltd.
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Gleitman, H., Fridlund, A.J., Reisberg, D. (1999). Psychology. New York. W.W.Norton & Company.
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Lang, G. & Teahan, R. (2001). Perspectives in psychology: support material. NEAB GCE A and AS Psychology.
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Staddon, J.E.R. & Ettinger, R.H. (1989). Learning – An introduction to the principles of adaptive behaviour. New York. Harcourt Brace Jovanovich, Inc.
