The method of classical conditioning is based on Pavlov's work, which was briefly introduced in Chapter 1. Pavlov himself was usually fairly cautious in his claims, but did make one or two comments to the effect that many forms of action were `nothing but' collections of conditioned reflexes. There is still considerable debate about how far the results obtained by Pavlov apply to everyday life. Some of the issues in this debate are sketched in here, before we look at Pavlov's findings.
Operant conditioning and classical conditioning. One rather theoretical problem is whether or not one may classify different types of conditioning. There is some measure of agreement on the possibility of distinguishing two different laboratory techniques: operant and classical conditioning. Operant conditioning is described in detail in the next two chapters, and some of the distinctions between it and Pavlov's methods will be obvious. The main factor is whether or not striving to achieve a goal is a characteristic of the behaviour which has been conditioned. Although this is a very loose way of talking about conditioning, it is a good rule of thumb for choosing between the technicalities of the two types. If the conditioned behaviour is essentially a rather inflexible and automatic reaction to a particular stimulus or situation, then it is more likely to relate to classical conditioning. But if there is some achieving of goals, avoidance of punishment, or even un
rewarded striving, we are more likely to talk about operant or instrumental conditioning (see Chs. 3 and 4).
Responses that can be classically conditioned. Pavlov's first experiments were with the response of salivary secretion, and by and large classical (or 'Pavlovian') conditioning applies best to involuntary or emotional reactions. Many of these have the distinction of being controlled by a special part of the nervous system, the `autonomic nervous system', which usually deals with digestion, breathing and so onand does not involve much conscious effort. Many responses that we can almost never be directly aware of may easily be conditioned : changes in electrical resistance of the skin, changes in heart rate, blood pressure and various types of electrical brain rhythms. Many of these `autonomic' responses, such as skin resistance and heart rate, are closely connected with emotional states, and it seems inevitable that at least some of our more `reflexive' emotional reactions are coloured by classically-conditioned associations. Visual symbols such as national flags, the swastika, hammer and sickle, or cross usually have a very direct emotional impact, apart from any reasoned considerations that may be added on to it. Words with powerful associations may also elicit direct emotional reactions before we have had time to `think about the words : e.g. fascist; IRA, sex, unemployment. Generally speaking, emotional reactions and individually classically-conditioned responses are involuntary, in that it is very difficult to decide to salivate, or be angry, or in the absence of any appropriate stimulus; it is also very difficult to decide not to salivate or be angry if a strong signal for those reactions occurs. With sufficient training and practice, actors may decide to have any of a range of emotional reactions, and physiological tests have confirmed that expert yogis in India can make voluntary decisions about autonomic responses such as blood pressure and heart rate. But there is a monumental difference in degree between the difficulty of such expert control and the unavoidable simplicity of conditioned emotional associations.
The clearest example of an experiment which shows classical conditioning uncontaminated with other factors is the one
showing that involuntary knee jerks could be conditioned to the sound of a bell, if the bell was always rung before the knee was tapped. The unconditioned stimulus (US or UCS) of the tap on the knee has relatively few effects on the subject apart from the one intended. However, giving food to hungry dogs, as Pavlov did, may have many other psyhcological effects apart from eliciting salivation. The dog may enjoy the experiment far more than one where painful stimuli were used, and wag its tail and strain towards the food bowl when the conditioned stimulus is presented. A popular method of studying classical conditioning in human subjects is that of linking eyeblink responses to sounds or faint lights by making these stimuli signals for a short puff of air to the eye. People who undergo this procedure start by blinking when air is puffed at their eye, but soon begin to blink when a signal which precedes the air puffs is presented. A problem with this method is that blinking occurs every few seconds as a matter of course, and blinking may also be done voluntarily, or nervously, by some subjects.
Notwithstanding these difficulties, a wide range of techniques have been developed with laboratory animals such as
Fig. 3.1 Various phases of classical conditioning. The progress of conditioning is marked by changes in the strength of the CR (con ditioned response) e.g. the number of drops of saliva secreted when a stimulus is presented. In conditioning the CS is always followed by the UCS and then in extinction the CS is given by itself. In discrimination one stimulus is a signal for the UCS but a second stimulus is not.
rats, pigeons and monkeys, and data collected by these methods, together with the data from human subjects, provide a wealth of evidence by which to judge Pavlov's original discoveries. Although new aspects of conditioning have been investigated, and many new theories to explain classical conditioning have been put forward, the great mass of accumulated data confirms facts of conditioning named by Pavlov and his contemporaries.
The Pavlovian experiment
In the conditioning apparatus used by Pavlov a dog is loosely restrained on a stand with a tube running from its cheek to allow very precise measurement of the volume of saliva it secretes. It is hungry, and every five minutes or so a small door opens in front of it and a small amount of food is pushed out. When the dog sees the food it starts to salivate, and this can be measured by the experimenter from recording apparatus in the next room. The experimenter has remote control of buzzer and lights and similar signalling devices, so that a signal can regularly be presented just before the food, or at other times.
Acquisition of the conditioned response. This term is commonly used for what Pavlov called the establishing or development of' the conditioned reflex. It applies to the phase of an experiment in which the CS (conditioned stimulus) begins to provoke responses usually only given to the UCS. In Pavlov's experiments this would be the phase where a dog starts to salivate when the CS, for instance an electric buzzer, sounds, as well as salivating when food is presented.
Figure 3.1 shows how the initial acquisition phase can be plotted as a gradual increase in the strength of the conditioned response (CR) from trial to trial. (Trial is often used in the sense of trial run, to refer to a presentation of the experimental stimuli.) Although it is the changes in response that are measured, Pavlov emphasized that it is the changing function of the stimulus which is theoretically vital. The acquisition of the CR can be interpreted as 'stimulus-substitution', since the CS comes to serve as a substitute for the UCS. We might put it rather loosely this way : in a Pavlovian experiment the dog learns that the CS means food.
Extinction and spontaneous recovery. Suppose that after acquisition,
when the CS was accompanied by food, the CS were to be presented over and over again without any food. Would the dog go on salivating? In some circumstances (see Chs. 4 and 5) a CR may persist for a remarkably long time. However, as a rule in the Pavlovian experiment, the CR diminishes quickly when food is withheld and the CS is given by itself. Why is this? In Pavlov's theorizing, it was suggested that a direct connection between the CS and UCS was formed in the brain during acquisition; it would therefore be simplest to assume that the same connection was gradually destroyed in extinction - the period when the CR slowly disappears. But `spontaneous recovery' of the CR, after a period of rest (as shown in Fig. 3.1) proves that some association between the CS and UCS has remained intact despite the waning of the response in extinction. Pavlov's explanation was that the original association was not broken, but somehow pushed to one side by a process of inhibition. The details of this process are obscure, but the `inhibition' concept has proved useful for dealing with the suppression of conditioned responses in extinction; they are apparently never completely forgotten.
Discrimination and generalization. The inhibition concept also comes in useful for interpreting the effects of stimuli which become signals for `no food'. If a buzzer is used as the signal for food, a dog will salivate for a sound that_ bears almost any resemblance to the buzzer, although the amount of salivation will be less and less for sounds that are more and more unlike the proper signal. This responsiveness to stimuli because of their similarity to a CS is called stimulus generalization. However, dogs can make extremely fine auditory discriminations with the benefit of experience, as is evident from the habit, seen in many household pets, of anticipating the arrival of a familiar person on the basis of footsteps, or even car noises. Obviously when such a fine discrimination has been established, stimulus generalization has been drastically reduced.
Pavlov's experimental study of discrimination was accomplished by presenting positive and negative conditioned stimuli to the same animal. The positive CS signals food, but the negative CS signals `no food'. With enough experience of these circumstances, a dog may become conditioned to salivate to the positive CS, but not to the negative CS. This kind of discrimination may be demonstrated using only two stimuli, such
as a high-pitched and a low-pitched tone : if only the highpitched tone is followed by food, the dog learns to salivate only to the high-pitched tone, and not to the low tone. Pavlov also used some rather complicated combinations and sequences of stimuli to demonstrate the inhibitory properties of a`no food' signal. He gives one example of a dog first trained with three separate positive signals : a flashing light, a tone of C sharp, and a rotating disc. All these were signals for food and made the dog salivate. Then an `inhibitory combination' was formed by sounding a metronome along with the rotating disc, and not giving food with this combination so that the dog learned not to salivate when the metronome tick and rotation occurred together. Now the inhibitory effects of the metronome could be tested by sounding it along with the other positive signals of the tone or the flashing light. When this was done the usual salivation produced by the positive signals was virtually eliminated. Having taken the precaution of showing that the metronome would not suppress salivation before it was used as a 'no-food' signal, Pavlov felt justified in concluding that the metronome had become a conditioned inhibitor. In other words, some stimuli which do not provoke a conditioned response are not neutral, but. are signals for suppressing the response. This notion is common in theories of discrimination learning, which are discussed in more detail in Chapter 8.
Conditioning and the biological clock. Although very definite stimuli such as-buzzers and light flashes are used for most experimental purposes, conditioning may take place with much more subtle signal sources. One internal signal source which is very indefinite, but seems to work accurately, is the `biological clock' - a name given to some mechanism which is presumed to allow judgement of time without external clocks. Dogs fed on the hour every hour will salivate `on time' if a feeding is missed out, and time intervals are involved in the delay- and traceconditioning forms of the Pavlovian procedure. In delay-conditioning the CS starts several minutes before the food is due, instead of the usual few seconds, and continues until the UCS (food) is delivered. Trace-conditioning is similar except that the CS is turned off some time before the UCS appears. In both cases sufficient training results in the `timing' of the CR so that most salivation occurs just before food is due. This suggests
that the conditioned stimuli may initiate timing processes which in turn produce the conditioned responses.
Conditioned conditioned stimuli. A very strong CS, that is, one which reliably leads to much salivation, can be used instead of food to induce salivation in response to a new cue, which therefore is never actually paired with food. This is not very easily done, but Pavlov quotes a successful case where salivation was first conditioned to a buzzer. A black square was then held in front of the dog for ten seconds and followed after a break by the buzzer. After ten of these pairings the dog salivated a small but significant amount at the sight of the black square. Since food was never given in conjunction with the black square, steps had to be taken to prevent it becoming a`no-food' signal and that is the reason for the break between the square and the buzzer. This type of higher-order conditioning has rarely been extended beyond the second order, but a long sequence of individual stimuli may be established, if there is always a reliable UCS at the end of it. Dogs given unpleasant injections very soon react at the sight of the syringe (Pavlov, 1927) and, equally, human activities which are advance preparations for going out for walks or providing food are not lost on dogs interested in the usual outcome of the preparations.
Backward conditioning. It is virtually impossible to obtain conditioned responses to a CS which begins after the onset of the UCS : if a dog is already eating, buzzers and lights tend to be ignored, and may not make the dog salivate if they are turned on without the food, even if they have accompanied eating and the after-eating period many times. It is hard to imagine why backward conditioning should be so difficult with stimuli which condition very easily if they are used as advance signals for food in the normal Pavlovian way. It may have something to do with the `blocking' of attention to less important events once the more important UCS has started (see Ch. 8). Whatever the explanation, practically all experiments which have compared backward conditioning with the normal forward conditioning procedure have found backward conditioning much less effective for both animal and human subjects.
Words as signals. `Speech provides stimuli which exceed in richness and many-sidedness any of the others, allowing comparison
neither qualitatively or quantitatively with any conditioned stimuli which are possible in animals'. (Pavlov, 1927, p. 407.) Language is said to provide us with a second signalling system in which words can serve as substitutes for things (see Ch. 9). There are many different ways in which words can be interpreted as conditioned stimuli but Pavlov and Russian psychologists influenced by him have been particularly interested in the way in which words in the form of instructions can directly elicit human actions. An extreme case of this is seen in hypnotic suggestion, which interested Pavlov, but Luria (1961) has considerably refined the concept of speech as a method of eliciting behaviour by showing how susceptibility to instruction, and later the use of self-instruction, develops in young children. (See other volumes in this series for further information about cognitive development and language.)
Conditioning processes and personality. Pavlov rapidly came to the conclusion that the dogs which took part in his experiments could be classified into personality types. At first he chose dogs that were very lively and friendly, only to find that these animals went to sleep during the experiments at the first hint of monotony. When dogs who were generally shy, nervous and quiet were tested, they turned out to be more convenient, in so far as they stayed awake during even the most tedious experimental routines, and made very reliable and precise conditioned responses. It looked as though there were two definite personality types: `The first needs a continuous and novel succession of stimuli, which may indeed be absent in the natural surroundings; the other, on the contrary, needs extremely uniform conditions of life.' (Pavlov, 1927, p. 287.)
These categories correspond to the classical sanguine or phlegmatic types, or the modern distinction between extrovert and introvert, which is to some extent based on Pavlov's ideas (Eysenck, 1973).
Another dimension of personality is resistance to stress, or stability, versus neuroticism. A kind of neurotic breakdown in general behaviour can be observed in animals in two kinds of situation : first if they are exposed to extremely intense or unpleasant stimuli, and second if they are in a situation of unresolvable conflict between alternative responses. Examples of these two stresses given by Pavlov were the major flood in Leningrad in 1924 which had traumatic effects on the 'inhibitable'
dogs, and an experimental procedure which produced conflict by using a circle as a correct signal and an ellipse as an incorrect signal, with the ellipse being made rounder and rounder until it was extremely difficult to distinguish the ellipse from the circle. Some dogs were able to cope with stresses of these kinds, but others became over-excitable, with excessive barking, and biting of leads (these would be the neurotic extrovert type); still others became very withdrawn and unresponsive and lost weight (the 'inhibitable' or neurotic introvert type). Modern research is directed towards the question of how far characterization of human personality, based on questionnaire answers or clinical description, can be related to variables such as arousal level (see Ch. 2) and conditionability.
For a recent conditioning experiment, young men in Australia were asked to watch a travelogue film about London. They must have been well aware that the film might be slightly unusual, since they had agreed to have measuring devices attached to their penises while it was being shown to them. They were not disappointed in this expectation, since the travel film was interrupted every minute or so and replaced by ten seconds of a film showing an attractive and naked lady. It was intended that the lady should be associated not with views of London, but with an arbitrary conditioned stimulus, a red circle, which signalled the brief episodes in which she appeared. The exact form taken by interruptions of the travel film was that the red circle appeared for ten seconds and was immediately followed by ten seconds of the nude female figure.
The results of this experiment (Barr and McConaghy, 1972) clearly showed the classical conditioning of sexual arousal. First of all there was an unconditioned response (UCR) : practically all the subjects had some degree of penile erection during the nude scenes (even small changes in the state of the penis can be accurately recorded with appropriate measuring devices). But by the time the red circle had preceded the nude scene on five or six occasions penile erection also occurred during the red circle presentations. In Pavlovian terms the red circle was now a conditioned stimulus for sexual arousal.
In a similar experiment an artificial fascination with foot-
wear was induced in male volunteers by showing slides of black knee-length boots just before slides of nude females. Apart from acquiring physiological responses to pictures of the boots, the subjects reported that the boots aroused sexual ideas and feelings, which generalized to other kinds of boots, black shoes, and in one case even to sandals (Rachman and Hodgson, 1968).
Such results add support to the suggestion that many human emotional states become identified with triggering situations through processes akin to classical conditioning. Other factors are undoubtedly involved in normal (and abnormal) emotional development, but the classical conditioning procedure supplies a relatively straightforward technique for attempting to alter emotional attitudes to particular stimuli in the course of therapy.
Aversion therapy is a method used in attempts to establish a negative emotional reaction to stimuli judged to have too strong a positive attraction - mainly in cases of alcoholism or homosexuality. It consists of the Pavlovian procedure of pairing unpleasant events, usually electric shocks or druginduced nausea, with the target situation, though opinions vary as to whether additional elaborations of the basic pairing are necessary. A method like this is hardly a satisfactory solution to the problems that may be raised by alcoholism or homosexuality, and could be made unnecessary by alternative approaches to treatment. But it has provided some respite from unwanted impulses for people who desired it, and continues to be used occasionally for this reason. For instance, Marks, et al. (1970) reported that a reduction in the unwanted activities and fantasies of male transvestites, fetishists and sadomasochists, produced by an aversion treatment, lasted throughout the followup period of two years. The treatment had relied on pairing electric shocks with both overt behaviours (e.g. dressing in women's clothes) and fantasies during a two-week stay in hospital. They also reported however that similar treatment had no long-term effect on patients who wished to change their sex.
A more indirect way of altering sexual impulses involves using slides or films as conditioned stimuli, as in the experiments above. A considerable amount of data suggests that the attractiveness of homosexual activities can be reduced by this means. The procedure is to use slides of men, which are initially sexually arousing to the patient, as signals for electric shocks. It is not surprising, perhaps, that the slides lose their
attractiveness, but it is rather unexpected that the process generalizes to homosexual fantasies and activities outside treatment sessions, so that these too may become less attractive.
Aversion therapy has been used more frequently with alcoholics than with any other category of patient. In follow-up studies to evaluate the effects of aversion treatments for alcoholics, it is generally found that about half of those treated abstain from drinking for at least a year afterwards. That does not sound very promising, but this relapse rate compares favourably with other forms of treatment. With no treatment at all it is very rare for alcoholics to give up drinking or return to normal drinking (Meyer and Chesser, 1970).
Counter-conditioning to remove anxiety. It is widely believed that anxieties and fears may result from previous unpleasant or tragic experiences, which is consistent with explanations in terms of conditioning. A well-known experiment by Watson and Rayner (1920) demonstrated the conditioning of a fear in `Little Albert', an eleven-month placid child who initially showed a fondness for white rats. This fondness was quickly replaced by fear after the sight of the white rat had been followed on six occasions by the loud crash of a steel bar being hammered. The fear was still apparent when Albert was tested five days later, and generalized without further conditioning trials to a white rabbit and a seal-skin coat which had previously caused no alarm. But if fears and anxieties have been conditioned-in, can they be conditioned-out? The finding of spontaneous recovery after extinction, referred to earlier, suggests that some remnant of any conditioning experience persists even if the conditioned response lapses. However, I have already described in the last chapter how some forms of behaviour therapy manage to reduce anxiety simply by exposing patients to the anxiety-provoking stimulus in an altered form; either progressive changes in a tolerable version of the stimulus (desensitization) or confrontation with an extreme form (flooding). More often than not, though, in these kinds of therapy, an attempt is made actively to condition-in a new response to replace and counteract anxiety. There are many physical and emotional responses which serve as distractions or comforts in the face of worry or agitation : whistling, singing, talking, smoking, eating, drinking, pacing up and down. But of course the effect of these is usually temporary, and in many cases excessive
eating, drinking or smoking related to anxiety constitutes a problem in itself.
Deep muscular relaxation on the other hand has few unwanted side effects and is used almost universally when an anxiety-reducing response is needed in desensitization therapy. Patients are usually trained to relax by practice in alternately tensing and relaxing different muscle groups, although hypnosis or tranquillizers are sometimes included to assist training, and occasionally as a substitute for voluntary relaxation. Once a reliable procedure for relaxation has been established, the goal is to make relaxation the CR to stimuli that formerly caused anxiety and tension. In theory, this requires that the anxiety-provoking stimulus is used as a CS which signals a state of relaxation. In practice, it is found sufficient that patients maintain a state of relaxation while imagining progressively `worse' situations, and it seems as though the relaxation allows the patient to get used to, or habituate to, the feared stimulus. As with most methods of therapy, there is some disagreement about exactly why desensitization works, and there are probably several reasons for its success. The 'counter-conditioning' principle is more directly visible in therapy where a more active response is trained to replace anxiety. In assertion training and some forms of, sex therapy it is more obvious that assertive behaviours are being used to replace anxiety associated with shyness, or sexual behaviours used to replace anxiety to do with sex.
Conclusion and summary The laws of classical conditioning were established by measuring the secretion of dogs' salivary glands and can be seen to apply best with similar responses, that is responses which are involuntary or controlled by the autonomic nervous system. In particular this includes aspects of emotional reactions. In a wide sense, classical conditioning means that stimuli paired together in time become associated, responses given to one being also given to the other. Experimentally, one of the stimuli usually precedes the other, when they are paired, and the major effect is then that responses given to the second come to be made, in anticipation, to the first stimulus. If, subsequently, the leading stimulus occurs repeatedly by itself, the conditioned response dies away (extinction), but there is a residual effect which allows for spontaneous recovery. Speculation, supported by experi-
ments with human subjects, suggests that previouslyexperienced associations govern human emotional reactions. Modifications to emotional reactions may be brought about in the course of therapy by using classical conditioning procedures, either by associating withdrawal from painful stimuli with impulses to be suppressed, or by associating relaxation with stimuli which evoke undue anxiety.