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The aim of this paper is to acquaint the reader with current scientific knowledge and understanding of the nature of hypnosis.


Go into any large bookshop nowadays and you will most likely find that their shelves are liberally stocked with books about hypnosis and its numerous applications. Pick out any such book at random, open it anywhere and look anywhere on the page. The chances are that what you are reading is plainly wrong, is misleading, is questionable, has little support, or requires significant qualification for it to be accepted as a valid statement.

There are several reasons for this that have a great deal to do with the history of hypnosis as well as the personal agendas of those who earn a living from practising and writing about hypnosis. Let us not be detained by this now, but note that one reason people may give for this state of affairs is that hypnosis is a phenomenon that is not very well understood and therefore there is bound to be a variety of equally tentative ideas and claims, with much argument and disagreement as to their relative merits.

This is an easy option and one that I do not accept. The time has passed for the 'all shall have prizes' attitude that prevails amongst those who use hypnosis clinically (I acquit most experimentalists of this offence): the rigorous application of scientific discipline (with Occam's razor ever close to hand) is now the order of the day. If such were a requirement of all aspiring authors of books on the subject, the space occupied by their efforts in our bookstores would be much less than it is at present.

The reality is that most of what is observed and experienced when hypnosis is said to be taking place (in the clinic, in the laboratory, on stage, on training courses, and so on) is not really so mysterious and can be satisfactorily explained provided we ground our explanations in a modern scientific understanding of the human mind, namely mainstream psychology and its related disciplines. Yet many writers have neither the knowledge nor the inclination to do this. I have lost count of the number of books I have seen which, on their covers, announce that their authors 'at long last divest hypnosis of the mystery that has surrounded it' while between the covers they do the exact opposite, often by appealing to some magical entity called 'the unconscious mind', pop psychology, and oversimplified notions of the human brain.

Historical antecedents of hypnosis

Mesmer and mesmerism

Although it is possible to compare therapeutic hypnosis with certain healing practices carried out in ancient Egypt and Greece, modern hypnosis, as most people are aware, may be traced back to the ideas and practices of the Austrian physician Franz Anton Mesmer (1734-1815).

Mesmer, in his dissertation in 1766, proposed the existence of a universal fluid that he eventually called 'animal magnetism'. Illness was associated with disturbances in the natural flow of animal magnetism in the body and Mesmer had the ability to restore this and thus heal the patient. He first used magnets but later found that his hands were just as effective and he would make slow passes over the patient's body from the head to the toe.

In 1768 he moved from Vienna to Paris where he set up group healing salons. There would be several large 'baquets' - tubs filled with water and iron filings, 'magnetised' by Mesmer. Rods protruded from each and the patients sat around and applied them to their afflicted parts. Some of the patients would have 'a crisis'; they would faint and go into convulsions, shaking, crying, laughing hysterically, and so on. Finally they would appear to enter some kind of stupor with a glazed look in their eyes. The scene must have been extraordinary!

A modern definition of hypnosis

Let's now move forward 240 years and compare what I have just described with a modern definition of hypnosis. Here is the first part:

Hypnosis is a process in which one person, designated the hypnotist, offers suggestions to another person, designated the subject, for imaginative experiences entailing alterations in perception, memory and action (J.F. Kihlström, page 21).

Let me give some examples of suggestions.

So far the definition only describes the activity of the hypnotist, but how different from that of Mesmer! Now consider the response of the hypnotic subject:

(T)hese experiences are associated with a degree of subjective conviction bordering on delusion, and an experienced involuntariness bordering on compulsion (op. cit.).

That is, the subject's experience is characterised by a sense of involuntariness (e.g. in the case of suggestions of movement or inhibition of movement) and reality, in the case of suggested perceptual experiences. But no histrionics, no falling about, no stupor.

How the practice of hypnosis today and the theories that try to explain it evolved from the methodology and theory of mesmerism is a fascinating and instructive story. This evolution is summarised in an overview of the history of hypnosis in Heap & Kirsch (2006), xxiv-xxv:

'This overview reveals stages in the evolution of modern hypnosis that reflect the cultural and scientific attitudes and practices that prevailed at various times.

'Firstly, we have its origins as a healing practice, namely mesmerism, rather than a normal psychological process or phenomenon. The setting for this is eighteenth century France in the Age of Enlightenment and, although Mesmer explained his procedures by reference to an imaginary entity, namely an invisible fluid that he called 'animal magnetism', he endeavoured to relate this to ideas and discoveries from the natural sciences of that time.

'Next we see the application of more critical thinking and the shedding of superfluous practices such as mesmeric passes and crises. Along with this we have the development of psychological, rather than physical, explanations for the observed phenomena. Hypnosis then emerges not primarily as a treatment but as a psychological phenomenon for scientific study in the laboratory with normal individuals. Theorising accordingly becomes grounded in existing mainstream psychology and its related disciplines. Correspondingly, we have the more systematic investigation of the therapeutic effectiveness of hypnosis in the form of controlled clinical trials rather than anecdotal evidence.

'This process continues to evolve with, for example, the application of theories and research grounded in current neurocognitive approaches, and neurophysiological models that are investigated by brain imaging techniques.'

The four fundamentals: the traditional model

To understand modern hypnosis it is essential to escape from the agenda set by its historical roots as a form of treatment and to leave out any consideration of its practical applications in medicine and psychology. Specifically we need to get to grips with four fundamental concepts.

The four concepts are suggestion, suggestibility, induction and trance (or 'the hypnotic state'). It is important to be able to define all four as objectively as possible, to examine their properties, to be able to measure these properties in reliable and standard ways, and to elucidate the relationships between all four.

This describes much of the experimental research that has been undertaken on hypnosis over the last 50 years and more, and which continues. The research is largely written up in learned journals and textbooks. In my experience, people calling themselves 'hypnotherapists' (and, for that matter, stage hypnotists) have little awareness of this literature. This is probably because most of them do not have a background in academic psychology. It is also likely that, because their methods are based on ideas about hypnosis that are incompatible with the results of this research, it is not really relevant to their trade.

Although much has been learned from this research, it has been very slow in clarifying even the most basic theoretical issues such as those summarised above. There are a number of reasons for this; I shall not go into these except to say that for many years a fundamental controversy has raged that has polarised opinion amongst the scientific hypnosis community, to the extent that the most eminent authorities on hypnosis, including distinguished professors of psychology and psychiatry, are often identified according to which side of the controversy they support.

To understand this controversy it is necessary for us to remind ourselves of the traditional or classical model of hypnosis. Firstly, we have a hypnotist and a subject (or it could be a group of subjects). The hypnotist performs a hypnotic induction on the subject and places him or her in a trance. One of the properties of this trance is that the subject becomes very responsive to suggestion. There are, however, inherent differences between people in their level of suggestibility, some being highly suggestible, some being very resistant to suggestion, and most lying somewhere in between.

The hypnotic trance is considered to be a special altered state of consciousness into which the hypnotist places the subject. Moreover, hyper-suggestibility is not the only property that has been traditionally claimed for the hypnotic trance. Other alleged properties have included hyper-obedience or automatism, profound insensibility to pain, ability to perform superhuman or even supernatural feats, hypermnesia (the ability to remember accurate details of even remote events in one's life), extreme literalism, and access to 'the unconscious mind'.

Traditionally, trance is endowed with the property of depth: subjects enter a light, medium or deep trance. It is claimed that the properties listed above, and others, are enhanced with increasing depth of trance. For example, subjects are alleged to become responsive to more profound suggestions as they enter a deeper trance. So, to respond to a suggestion of arm lightness and levitation, one only need be in a 'light trance', but to respond to a suggestion of a complete or near absence of the sense of pain or of a visual hallucination requires a 'deep trance'. One indication of the depth of trance therefore is the subject's responsiveness to different suggestions. A minority of individuals are only capable of entering a light trance; another minority can achieve a deep trance; and most lie somewhere in between. This characteristic is regarded as being stable for any given individual and is often treated as being equivalent to suggestibility.

Trance is induced by means of a hypnotic induction: typically the hypnotist encourages the subject to narrow his or her attention onto just one stimulus, image or idea, and repeats in a monotonous voice suggestions that he or she is becoming relaxed, tired, drowsy and sleepy. Later stages of the induction are known as 'deepening' procedures for obvious reasons and, whereas the initial stages of the induction often use an external stimulus for fixation (e.g. a spot on the ceiling), deepening procedures usually have an internal focus of attention such as a relaxing fantasy.

Hence the pivotal concept in this account of hypnosis is the trance. It is pivotal because it is used to explainthe various phenomena that are observed or claimed to arise during hypnosis (i.e. following a hypnotic induction) as listed earlier. Thus the subject, in response to the hypnotist's instructions, moves an arm without conscious effort or is unable to move it; sees, hears and smells things that are not there; feels no pain when pricked with a needle; forgets things he or she has just been told; thinks he or she is a child again, and so on because he or she is in a trance and not through acting or pretence.

This way of conceiving hypnosis is reflected in the language that is still used to describe how a session of hypnosis is conducted. That is, we say that hypnosis is 'induced', that subjects 'enter hypnosis', are 'hypnotised', are 'in hypnosis' or 'under hypnosis', and are 'dehypnotised or 'brought out of hypnosis'.

The four fundamentals: modern ideas

The traditional model of hypnosis, as just described, remains the one to which most people - hypnotherapists, writers, journalists, protagonists of alternative medicine, and the public in general - seem to subscribe. And yet, modern research, mainly conducted in psychology laboratories at universities, has indicated that virtually everything that has just been said is wrong or unsubstantiated!

The weak link in the model is the notion of trance and, in particular, its use as an explanatory concept. This issue is at the core of the battle that has raged in academic circles for the last 60 years (although the controversy can be traced much further back than this). Only in recent times has the dust settled and some kind of consensus is now emerging.

The 'battle' I am referring to has involved those who believe that the idea of hypnosis as a 'special state' of the mind (and brain) remains central to an understanding of hypnotic phenomena and those who consider that it is unnecessary and unsupported by any convincing evidence. The former are know as 'special state' or 'special process' theorists and the latter as 'non-state' or 'socio-cognitive' theorists. The term 'socio-cognitive' acknowledges that these theorists believe that all the phenomena associated with hypnosis can be explained by processes known to social psychologists and cognitive psychologists and do not involve any altered state of the mind. Increasingly in the last 50 years, non-state theorists have amassed a great deal of laboratory evidence to support their position. This evidence is vital to an understanding of hypnosis even though there are several different non-state theories, and even if you still maintain a special-state position.

For the purposes of this article I am not going to discuss in any depth the various non-state theories but I shall fast-forward to what I believe the accumulated evidence is currently telling us about the nature of hypnosis. I do not believe that mine is a controversial position and it does not rule out the contribution of any of the current major theories, state or non-state.

Firstly, it seems clear that compared to former times, there is now much less emphasis on the concepts of hypnotic induction and hypnotic state or trance and much more on suggestion and suggestibility. Let us therefore start by considering what we mean by 'suggestion'.

In various writings (e.g. Heap & Aravind, 2002) I have defined a suggestion as follows:

'A communication, conveyed verbally by the hypnotist, that directs the subject's imagination in such a way as to elicit intended alterations in sensations, perceptions, feelings, thoughts and behaviour.'

So, responding to a suggestion means that you go along with the words and ideas of the hypnotist and the images that he or she describes, and have some of the responses and experiences that you would have if the suggested ideas were happening in reality. In fact, suggestion occurs in everyday life: for example if I suggest to you that right now you are chewing a very sour lemon, you might react accordingly, say by experiencing a sour taste in your mouth and even producing some extra saliva.

As with the first part of the earlier definition of hypnosis, so far we have only described the behaviour and intentions of the hypnotist. What should we say about the responses of the subject?

'Suggestions differ from everyday kinds of instructions in that they imply that a "successful" response is experienced by the subject as having a quality of involuntariness or effortlessness.'

(Please note that the terms 'involuntariness ' or 'effortlessness' are psychologically not the same as automatism or hyper-obedience.)

There is another way of viewing this and that is to use the term 'counter-expectational'. For example, normally if I said to you that your arm is going to float up in the air, it would come as a complete surprise to you if it did so without any apparent effort on your part. If I pinch the back of your hand you would expect to feel it, even if I said that you wouldn't. You don't normally experience a disgusting smell in your nostrils unless there is something actually present to produce that smell. Likewise, you wouldn't expect not to see these words in front of you, or fail to hear a clearly audible sound when you are listening for it, or immediately forget something that you have just heard me tell you, or be unable to stand up, just because I said you can't do any of these things. Yet all of these things appear to happen when some people respond to suggestion.

People differ in the degree to which they respond to suggestions. This quality we call here suggestibility but unfortunately writers also use the terms 'hypnotic suggestibility', 'hypnotic susceptibility', 'hypnotic responsiveness' and 'hypnotic responsivity', often interchangeably. Just for present purposes let us stick to the term suggestibility.

Several scales have been developed to measure suggestibility. These scales have a high degree of reliability. Each consists of a number of different types of suggestion that the investigator reads out, and the subject's response to each is assessed subjectively and/or objectively. The scores are summed to yield a total score that is the person's suggestibility as measured by that scale. Suggestibility scores in the general population bear a rough approximation to a bell-shaped distribution.

It is also important to note that these scales have high internal consistency. That is, scores for any one item correlate significantly with the total score for the remaining items. There is one, and indeed more than one factor linking the items - in fact possibly three major factors.

Most scales incorporate a hypnotic induction procedure but not all of them do and I shall take up this point again in a moment. I also need to make clear that in psychology there are a number of different types of 'suggestibility' and not all of these have any connection to suggestibility as it relates to hypnosis. So in other contexts, when you hear someone referred to as being 'very suggestible' it does not necessarily mean they are suggestible in the sense that we are presently considering the term.

People's scores on suggestibility scales are very constant (subjects have been followed up for as long as 25 years) and there is evidence from studies on twins that suggestibility is partly inherited. (In my opinion the stability of suggestibility and the reliability of individual difference are key factors in establishing the scientific credentials of hypnosis as a psychological phenomenon.) Non-state theorists, however, have often disputed whether suggestibility is indeed a fixed characteristic of a person in the same way as, say, certain personality characteristics or intelligence. Some, for example, have claimed that low scorers on suggestibility scales simply have the wrong attitude and approach to responding to suggestions and they can therefore be trained to increase their suggestibility. However, I believe that the weight of evidence is now strongly in favour of the position that suggestibility is determined by characteristics and aptitudes that are inherited or determined at an early age. I shall later refer to neurophysiological and neuropsychological evidence in support of this.

More on the nature of suggestion and suggestibility

So hypnosis is about suggestible people responding to suggestion in a way that they experience as involuntary and realistic. One problem with this description is that it clearly depends on the subjective experience of the person and we cannot observe this.

For example, if I am the subject and you suggest that my arm is becoming light and rising in the air I might simply lift it up voluntarily. If you suggest that I cannot feel anything when you pinch my arm I might say 'No' but I am lying. Likewise if you say, 'You can now smell your favourite perfume' I may say I can just to please you. In other words, people who seem to respond to these kinds of suggestions are merely being compliant. Deliberately so.

There is no reason to believe that this does not happen. However, there is no evidence that compliant individuals are more suggestible than those who aren't. And these days compliance is not regarded an essential feature of suggestibility.

Another possibility is that I am deliberately employing a strategy to try to achieve the suggested effect. Distraction is often considered as one explanation for effects such as suggested amnesia and analgesia. For example, if I suggest to you that you will not remember a list of words you have just learnt, the moment I test your memory you may direct your attention to other thoughts. When I test you to see if you have responded to my suggestion of analgesia, again you may distract yourself so your pain is not as noticeable.

In fact very suggestible people do not do as well in responding to a suggestion of analgesia when they are explicitly instructed to use strategies such as relaxation and distraction as when they are responding to suggestion. Also, being asked to keep attending to the area receiving the painful stimulus does not seem to have a great effect on the analgesia, whereas it does so in those people using explicit strategies (Eastwood, Gaskovski & Bowers, 1998).

It is however acknowledged that strategies such as these can indeed be a part of the explanation of hypnotic responding.

Could it be that suggested hallucinatory experiences are simply imagination? I suggest that your best friend is standing in front of you, or that you can vividly hear your favourite music being played or that you can smell your favourite perfume. Are highly suggestible people simply imagining these things, nothing more?

It is acknowledged that imagination is an important component in hypnotic responding. However the ability to imagine vividly (in the visual modality) is only weakly related to suggestibility. Also the suggestible subject reports that the experience in response to suggestion is much more 'real' than under instructions simply to imagine the experience.

So, what is it specifically about the way highly suggestible people respond to suggestion? What are they doing that is different from what less suggestible people do so that their experiences seem to be so involuntary and realistic?

The status of the induction

Let's put that question to one side for a moment because we have to consider now what the latest research has to say about the two remaining fundamentals of hypnosis, namely the induction and the trance.

First let us consider what laboratory research has taught us about the role of the hypnotic induction. The bad news is that there is little evidence that following a standard hypnotic induction people typically display the changes listed earlier - hyper-obedience, profound insensibility to pain, ability to perform superhuman or even supernatural feats, and so on. But what about hyper-suggestibility? The good news for the traditionalists is that, following an induction, on average there is an increase in suggestibility as measured by standard suggestibility scales. The rest of the news is not good at all. It seems that the increase is on the whole rather modest and does not occur for everyone, some individuals even being less suggestible following an induction (perhaps because they are averse to the idea of hypnosis). For example, Kirsch & Braffman (1999) found that after a hypnotic induction:

Hence the gains in suggestibility are modest. But why do these gains occur at all? The traditional answer is that they are due to the person being put into a trance.

However, most revealing of all is the finding that the hypnotist is at liberty to substitute the traditional 'focused concentration and sleep' (or relaxation) induction with a whole range of different scripts and, provided that the subjects' motivation and commitment remain the same, the increase in suggestibility will still occur.

For example, suppose, prior to administering a suggestibility scale (without an induction) we give subjects a series of instructions to the effect that we are shortly going to ask them to bring to mind certain ideas and situations and it is most important that they concentrate and use the full powers of their imagination to create the suggested images, the feelings, and the experiences, as vividly as possible. This procedure usually leads to increases in suggestibility scores equivalent to those when a classic induction procedure is used.

Now let's do 'an induction' that is the complete opposite of the traditional procedure. Instead of telling the subjects they are feeling more relaxed, tell them they are feeling more energetic! Say that, instead of narrowing their attention on their inner experiences, they are becoming more aware of everything that is happening around them, as though their mind is 'expanding'. In place of a comfortable chair or couch, provide them with an exercise bicycle and have them pedal constantly as you administer your 'alert induction' as it is called. Under such conditions suggestibility scores increase overall by the same margin as when a traditional induction procedure is used.

Laboratory experiments have even obtained the same results using 'sham' inductions such as inhalation of a gas (actually air) 'that has a powerful effect on suggestibility' or a pill with 'hypnosis' stamped on it!

What does all this mean? It seems that the effect of the induction on suggestibility is to prepare subjects to respond to the suggestions to follow, that is to enhance their commitment, motivation, expectation, and so on. You can do this with a traditional sleep or relaxation procedure, but you could choose any of the others described above, or even invent your own.

From this standpoint then, we may define an induction as any preliminary procedure that is intended to enhance a person's response to suggestion. Hence we can, for example, investigate different kinds of induction and ascertain which are the most effective for different kinds of individuals.

The status of the hypnotic trance

We have now got some idea of the modern, non-state or socio-cognitive approach to hypnosis and how it contrasts with the classical or traditional approach. But where does the former leave the concept of trance or hypnotic state?

It looks as though we can dispense with this notion altogether and some authorities are quite happy to do this. However many are not so disposed. There is in fact a reluctance to abandon the idea that during hypnosis a subject, whatever suggestions he or she is responding to, is in some special state of mind. (When it was discovered that subjects were just as suggestible after an 'active-alert' induction as a traditional induction, the investigators invented a new state of mind called 'the alert trance'!)

If the traditional view of hypnosis as an altered state is correct, can this state be reliably detected by any objective means? Some writers have cited observable behavioural and physiological signs as evidence that the subject is 'in trance' - relaxation of the facial musculature, facial pallor, suppression of the swallowing reflex, etc. However, it is difficult to distinguish these from those associated with a general state of relaxation. Also, what do we say when, during hypnosis, the subject is reliving an exciting or distressing memory and these signs will obviously be absent? Is he or she no longer 'hypnotised'?)

A reliable physiological indication of the trance state might be called the Holy Grail of hypnosis research. Let's look at this statement more deeply to understand why. (Incidentally, ignore any statements in the popular hypnosis literature to the effect that hypnosis is an 'alpha state' or a 'theta state' or that the right hemisphere is put into one of these states, or that the hypnotist directs suggestions to the unconscious mind in the right hemisphere by sitting on the subject's left side, or that the hypnotist matches the frequency of his voice with that of the subject's brainwaves, etc., etc.)

First consider other altered states of consciousness that have a physiological basis, such as sleep, concussion or alcoholic intoxication. Let's just take sleep as an example, specifically dream sleep. Suppose I do an experiment to see if people sweat more when they are in dream sleep than when they are in non-dream sleep. I use the same participants in both conditions and compare measures of sweating in each one.

Now, how do I know which condition the participants are in? The answer is that I could check their EEG patterns (brain waves) or observe their eye movements. (During dream sleep the eyes oscillate from side to side and this is observable even though the eyes are closed.) The experiment thus seems quite straightforward.

Now suppose that I do an experiment to see if people are better able to recall remote autobiographical events during hypnosis than outside of hypnosis. I test people's memory under two conditions, once when they are 'hypnotised' and again when they are 'not hypnotised'. Let's assume that I find no difference between the two conditions. 'Well', you might say, 'that may be because your participants weren't really hypnotised (or weren't properly hypnotised) when they were supposed to be' or even 'Your participants were actually hypnotised when they weren't supposed to be'.

But how do I know that the participants are 'properly hypnotised' in the hypnosis condition and 'not hypnotised' in the non-hypnosis condition? It would be ideal if I could check this, as with the experiment on dream sleep, with a reliable test for the presence or absence of hypnosis, say an EEG pattern or some other scan of brain activity while the participants are doing the memory test. We may call this a 'signature' of hypnosis (in this case a neurophysiological one). Currently no such signature is known. I shall return to this later.

One obvious answer to the question 'How do you know your "hypnotised" subjects were really hypnotised' is that they underwent a hypnotic induction, whereas the non-hypnotised group did not. This is probably the best answer we can come up with at the moment but in the context of the present discussion there are two problems. First is the question 'Can we be sure that the induction worked for some or even all of the participants?' For some reason in my experiment the participants may have resisted the induction or I might not have administered it properly. Second is the question 'How do you know it was a hypnotic induction?' There has to be some agreement that the procedure I used constituted a hypnotic induction but what are the defining characteristics that inform us that it was?

The latter problem is compounded by the fact that when some experimenters are comparing hypnotic and non-hypnotic conditions, in the latter they substitute the hypnotic induction with a time-filling exercise such as reading or listening to music. But what decides that these activities do not constitute a hypnotic induction? (In some experiments in which 'highly hypnotisable' participants have been used, it has been argued that during these substitute activities the participants may 'slip into' hypnosis and this may account for any lack of difference between the conditions described as 'hypnotic' and 'non-hypnotic'.)

From the standpoint of conducting scientific research this is all very unsatisfactory, yet little attention is ever paid to these difficulties in accounts of experimental research or how they can be addressed. Some people argue, however, that research using brain scanning methods has now shown that subjects are in a special state when they are hypnotised. So let us consider this evidence.

Neurophysiological evidence

In recent years there has been a growing number of laboratory studies that have examined the brain activity of people who are responding to hypnotic suggestions - for example suggestions for increasing or reducing the experience of pain, positive and negative hallucinations, and 'challenge' suggestions such as arm immobility. Areas of the brain have been identified that are most active when participants are responding to these suggestions. Significantly, high and low susceptible subjects have been compared and differences in the distribution of brain activity have been found, even when the participants are 'not hypnotised'. These findings are important as, for one thing, they refute the idea that hypnotic phenomena are not for real and that participants are, say, 'just acting'.

However, and this goes for brain scan studies in other areas of cognitive psychology, it is easy to be beguiled by this kind of research and to credit the findings with the same degree of sophistication as the technology used to achieve them. To play the Devil's Advocate for the moment, I could ask whether we would think much of an experiment that demonstrated that when a person is speaking there is evidence of an increase in activity (say measured by blood flow) in the articulatory muscles.

Well, that might be a little unfair. But there are a numerous difficulties with brain scan studies, partly because there are considerable individual differences in the patterns of activity observed, and the findings are usually presented in the form of averages of group data (and differences between groups). Because of this and other reasons I suspect that there is a danger that neurophysiological evidence will raise at least as many questions as it answers.

However, where I really part company with some of those who are conducting this research is their claim that at long last it has been proved that there is such a thing as 'a hypnotic state'. My counter-argument goes as follows.

Suppose we find that 'highly hypnotisable' subjects have a particular distribution of brain activity when responding to a suggestion of analgesia that is absent in 'low hypnotisable' subjects. Does this mean that their brain is in a special state at the time and that this explains their reported reduction in pain experience? Well, let's make a comparison with an everyday cognitive activity, namely performing mental arithmetic. During this task we can demonstrate that there is increased blood flow and metabolic activity in specific areas of the cerebral cortex, perhaps the left parietal and left frontal areas; increased neuromuscular activity in the articulatory apparatus associated with subvocal speech; more sweating on the palms of the hands; and increased heart rate. (Perhaps we can even demonstrate that mathematical virtuosos have a different pattern of activity from a person of average ability.) Do we say that this distribution of physiological activity constitutes a 'state'? Is the person is in a 'state of calculation', and this accounts for his or her experience? Surely not!

Moreover, to demonstrate that a specific neurological state underpins the subject's responses to any kind of suggestion implies that there is a unique signature that is present whatever hypnotic suggestion the subject is responding to (imagining sunbathing on a beach, reliving a traumatic experience, forgetting that the number 6 exists, experiencing profound amnesia, hallucinating an unpleasant smell, being a jockey in a horse race, etc.). These experiences are associated with vastly different patterns of brain activity that also differ considerably amongst individual subjects. It is a tall order indeed to think that, for all of these conditions and individuals, a constant neurological signature is present in the brains of each subject that defines 'a state of hypnosis', and that this is clearly absent when subjects respond to the same suggestions without hypnosis under the same pressures, demands and expectation and with the same degree of commitment.

The lure of reductionism

The idea that there are demonstrable alterations in brain activity during hypnosis and differences in such activity (as well as certain biochemical indices) between high and low susceptible subjects has persuaded some people that hypnotic phenomena can all be explained in physiological terms. This kind of thinking is known as 'reductionism'. It is a common tendency amongst those who study the human mind and behaviour nowadays to try to explain what is observed by reference to physical structures and processes (e.g. neuroanatomy, neurophysiology and, more recently, genetic constitution). There is an implicit assumption that those researchers who engage in this kind of work are the ones who are delivering the authentic account of the phenomena under investigation. Great kudos is now attached to scientific papers containing colourful brain-scan images that show bits of the brain lighting up under certain conditions or differences between groups of subjects performing the same mental task; likewise we are beguiled by announcements that scientists have discovered the gene that is responsible for some perceived human frailty or aberration such as dyslexia, criminality or homosexuality.

Such discoveries can be truly 'groundbreaking'; but many simply convey only the illusion of progress. Claiming that the differences between 'hypnotised' and 'non-hypnotised' people can be explained by neurophysiological processes belies the rich social psychological complexity of the hypnotist-subject relationship. The importance of expectation, demands, perceived role requirements and context in determining the behaviour and experience of the subject, and his or her own understanding of what happens, cannot be underestimated.

To illustrate this, there follows an extract from Heap (2000) in a paper on the supposed 'dangers' of stage hypnosis. At this point in my paper I am discussing why people tend to assume that participants in a stage hypnosis show have been put into a particularly 'deep trance'

'It is not difficult to understand why such assumptions are made. Typically the participants in a stage hypnosis show respond immediately and vividly to the suggestions given, as though they are indeed under the complete control of the hypnotist. Some of the stunts appear to call for quite unusual imagined experiences as, for example, when a young man is told that he has fallen in love with a broomstick, or when all participants are told that someone in the audience has stolen their 'belly buttons' and they must find out who it is. At other times, when they are not required to be active, participants may appear to have entered some kind of stuporous state as they sit slumped in their chairs. Sometimes an individual, noted for his or her calm and reticent demeanour, appears to undergo a personality change once he or she is up on the stage and has been 'induced'.

There is, in fact, no reason to believe that people will not behave exactly like the 'genuine' stage hypnosis participant if they are given enough incentive, such as money. However, the participants do not normally receive any material reward for their efforts. Nevertheless, some onlookers will simply interpret these activities as indicating that they are 'just acting'. Others, however, believe that they would only behave in the way they do if they were in some special mental state. This difference in interpretation is also evident amongst the participants themselves, some ascribing their outlandish behaviour to the fact that they were merely co-operating with the hypnotist, others having no ready and obvious explanation of why they responded in the manner they did, hence the explanation that the hypnotist puts them into a 'trance' and they are thus somehow under his or her power. Indeed the fact that the stage hypnotist usually carries out a 'trance-inducing' ceremony at the beginning of the act, and a 'trance-terminating' ritual at the end, serves to confirm this explanation. Moreover, because their behaviours and experiences are apparently so immediate and dramatic, people are inclined to believe that participants in stage hypnosis must be in especially deep trances or must be very deeply hypnotised.

'Despite this, the evidence from the hypnosis literature indicates that under equivalent contextual demands and expectations, and possessing the same cognitive skills, commitment and involvement, 'non-hypnotised' participants are indistinguishable from participants who have been ceremonially 'put into a trance'………

'This is actually implied in manuals of stage hypnosis …… and some stage hypnotists dispense with the 'trance-inducing' rituals altogether yet conduct their act in the same way ………

'One can therefore state with confidence that the salient determining factors in the behaviour and experiences of the participants at a stage hypnosis show are their own skills, attributes, and commitment to the task, the very definite expectations concerning how they should respond, the effect of audience pressure, the stage hypnotist's demands, and the effects of being amongst a group of participants ……….

'One manifestation of this is the difference in the quality of the responses of stage participants and that of patients undergoing hypnosis treatment. For example, a patient responding to the suggestion of imagining being a child again will generally remain relatively unchanged in his or her demeanour, though occasionally he or she may speak in a soft voice, more child-like than usual; stage participants on the other hand fidget, giggle, jump off their chairs and run around, fight with one another, and so on. When told that they are riding a horse (perhaps in order to re-create feelings associated with their favourite pastime) patients may again show little change in their behaviour except perhaps for slight rhythmical movements of the body; contrariwise, stage participants respond wildly, jumping up and down in their chairs, slapping their thighs, and so on. When given suggestions that they are feeling tired and sleepy, relatively little outward change is noted in the responses of patients, whereas stage participants slump in their chairs, drape themselves over one another, and even slide to the floor as though in a stupor. These differences in behaviour do not arise because the stage participants are 'in a deeper trance' or are 'more deeply hypnotised' than their counterparts in the clinic; in all three of the foregoing scenarios, patients in the clinic, despite minimal overt change, may report having profound and vivid experiences of the imagined or suggested effects. Clearly the differences arise because the demands on the stage participants are that they must be immediately responsive and give a highly visible and flamboyant performance for the entertainment of the audience. Such is decidedly not the case in the clinic'.

A possible meaning for 'trance'

Have I said all there needs to be said on the subject of trance? Not quite. We have seen that it is difficult to substantiate the traditional notion that the induction places the subject in an altered state of consciousness or trance or that it uniquely has the property of enhancing the subjects' suggestibility. However, there is a weaker version of the trance concept that many clinicians feel comfortable with. Some call this the 'naturalistic' trance because it is similar to how we use the term in everyday life. When we say, for example, 'Look at John. He's in a trance' or 'I must have been in a trance when I did that' we are referring to a absorption to use the terminology of cognitive psychology. We are so deeply engrossed in something that everything else 'goes into the background'. (Perhaps this is similar or identical to certain meditative states.) I should like to suggest one possible implication of this discussion for clinical practice.

Despite all that I have said about the weakness of the concepts of induction and trance, I do not advocate dispensing with the induction altogether, particularly when using hypnosis for clinical purposes. With each application of hypnosis it pays practitioners to consider what are the aims of the induction and deepening procedures in that particular case. With this in mind, along with the accumulated evidence on hypnosis, I have elsewhere (see below) proposed two definitions of hypnotic induction. One is that it is a series of suggestions that is intended to enhance the subject's responsiveness to the suggestions to follow; the second is that it is a series of suggestions that is intended to encourage a trance as understood by the term 'absorption'. The traditional induction and deepening methods, which emphasise mental and physical relaxation and pleasant imagery, tend to be more suitable for the latter purpose, while alert methods and inductions that enhance motivation and expectancy, and those that incorporate ideomotor suggestions such as arm levitation, are perhaps more suitable for the former purpose. For a discussion of the different applications of these two approaches to hypnotic induction, have a look in Heap & Aravind (2002).

Having said all this, I believe that it may still be the case that a minority of hypnotic subjects experience something that can be described as an altered state of consciousness (qualitatively different from a state of absorption) following a traditional hypnotic induction. However, these may not even be typical of highly hypnotisable individuals. This is not a theme on which I wish to elaborate here but recommend T.X. Barber (1999).

Some popular myths about hypnosis

As I stated at the beginning, for various reasons hypnosis has struggled to establish itself as a psychological phenomenon worthy of scientific consideration, and sceptics have often dismissed hypnosis in one short sentence: 'It doesn't exist' or 'There's no such thing'. When pressed to justify this, those who have bothered to read any of the scientific literature will usually cite the results of one or two experiments conducted by non-state or socio-cognitive theorists. But these studies are not concerned with determining whether hypnosis 'exists' or not. They are usually designed to test the idea that an altered state of consciousness is required to explain the responses and experiences of individuals undergoing hypnotic procedures. So hypnosis itself is not 'a myth'. There are however some very unusual and sensational claims that are often made about hypnosis and at this point I'd like to list some of those that have not been confirmed.

Hypnosis itself does not have the property to cause people to do things against their will - that is to make people hyper-obedient. The evidence indicates that in the situations in which hypnosis is undertaken (e.g. scientific experiment, treatment, stage act, etc.) the subject is already very compliant because of the demands and expectations of the context. And the hypnotist (as experimenter, therapist, entertainer, etc.) is usually in a position of authority or dominance with respect to the subject. For example, participants in experiments in the psychological laboratory often show a willingness to behave in a seemingly strange, dangerous or antisocial ways but hypnosis does not make them more willing in this respect.

Hypnosis does not improve people's ability to remember events or information any better by any similar procedures that involve relaxation and imagination. Indeed hypnosis on its own does not automatically improve ones abilities and skills other than enhancement due to increased motivation and expectation.

Hypnotic subjects are not compelled to tell the truth. They are able to lie just the same as they can without hypnosis.

There is little evidence to support the popular claim that hypnosis acts on, or allows access to, 'the unconscious mind' and little theoretical justification for this.

What a theory of hypnosis must do

As a prelude to answering the above question I would like to make explicit the approach that I consider to be most useful and least likely to set us off in the wrong direction. Responding to hypnotic suggestions, including those that make up the induction and deepening procedure, is something the subject does. This simple idea does away with expressions such as 'entering hypnosis', being 'in hypnosis' or 'under hypnosis', being 'hypnotised', 'coming out of hypnosis', and so on that impede a true understanding of hypnotic phenomena.

When you administer a hypnotic suggestion to a person, you are, in a way, setting him or her a problem, namely how to have the experience that you are describing. For example you suggest to subjects that their hand has become numb and insensitive and then you apply a slightly painful stimulus. Different subjects attempt to solve the problem you have set them in different ways - e.g. by using a relaxation method, or distracting themselves by counting, or concentrating on the suggested idea of numbness in the hand, or just waiting for the effect to happen. Only with some of your subjects will their response correspond with what you, the hypnotist, have in mind - that is a genuine experience of local anaesthesia that has an 'automatic' quality to it.

As we have noted, while responding to the suggestion, highly suggestible individuals tend as a group to have patterns of brain activity that are less characteristic of those low in suggestibility. What these difference in brain activity reveals is that, to achieve the suggested response, highly suggestible people are able to deploy certain skills in which low suggestible people are lacking. I believe that these skills are rather fundamental - that is they are inherited or acquired at a very early developmental stage - hence the consistency of suggestibility over time.

One consequence of this line of reasoning is that the various theories of hypnosis reveal the different ways - the different skills that may be deployed - whereby subjects may achieve, if they are able to, the suggested effects - compliance, relaxation, strategic enactment, role enactment, expectancy, dissociation, etc. However, it is those subjects who are able to experience the intended effects as realistic and as involuntary who are most likely to be the ones traditionally regarded as being 'good hypnotic subjects'.

There appears to be a consensus amongst academic psychologists who study hypnosis that any theory of hypnosis must account for the subjective experiences of involuntariness and realism that the suggestible subject finds so powerful.

One line of approach that is now popular is to consider that when responding to suggestion, the highly suggestible person is able to exclude from conscious awareness elements of the experience that would normally be available to consciousness. For example, when I raise my arm I am conscious of my arm lifting up and my intention to lift my arm. If however I am able to exclude from conscious representation my intention to lift my arm, it will seem to me that my arm is 'lifting on its own', i.e. involuntarily.

Similarly, if I am given the suggestion that my best friend is standing in front of me, I may make the effort to imagine him, to think of his voice, to imagine my feelings on seeing him, and so on. If I can remove from consciousness awareness the effort and intention that I make in creating this experience, then it will seem more like my friend is really there. To develop these ideas we can - and indeed must - use models and theories from mainstream cognitive psychology and neuroscience.

Let me now describe three experiments and challenge you to think about the possible explanations in terms similar to those I have just described.

Hypnotically suggestible subjects when given the suggestion that they cannot see a chair in front of them may report convincingly that they cannot see anything. Yet when asked to walk across to the other side of the room they walk around the chair. People who are told that they must only 'pretend to be hypnotised' usually bump into the chair (Orne, 1962).

Secondly we suggest to some very suggestible subjects that they can no longer hear their own voices. In the case of those who respond to this suggestion we then ask them to speak into a microphone that is connected to an amplifier and a pair of headphones that the subject wears. The amplifier causes a delay of say half a second in the subject's speech that he hears through the headphones. This is called 'delayed auditory feedback' and it is very difficult for people to speak coherently when at the same time they are hearing their voices delayed for a fraction of a second

What happens to those subjects who insist that they cannot hear their voice? With delayed auditory feedback their speech is disrupted as under normal conditions (Barber & Calverley, 1964)!

Finally, subjects learn a list of words and are then told that they cannot remember any of these words until a signal is given. Some very suggestible subjects may report complete or almost complete amnesia for the words. However they still show a characteristic electroencephalographic response when presented with words that appeared on the list Allen, Iacono, Laravuso, & Dunn, 1995; Schnyer & Allen, 1995) and this material still interferes with the subjects' recall of another list of words that was not included in the amnesia suggestion (Coe, Basden, Basden & Graham, 1976).

Some people think that the results of these experiments indicate that these very suggestible subjects are simply pretending. With no other evidence this is the best explanation. However, the further evidence that has accumulated has led most researchers to reject this explanation, although it is still entirely possible that some subjects may be pretending.

What seems to be happening in each of these experiments is that very suggestible subjects have the ability to exclude from consciousness awareness the explicit representation of the stimulus - hearing their voice, seeing the chair, or recalling the list of words. However, these stimuli are still implicitly registered in their behaviour and thinking in the usual way - their speech is affected by delayed auditory feedback, they avoid bumping into the chair, and the 'forgotten' material still interferes with new learning. This is a plausible way of understanding what is happening.

Hypnosis as a treatment

I am not intending to say much about hypnotherapy but will summarise my own perspective.

The traditional concept of hypnosis is associated with a range of treatment methods for medical and psychological problems. Some of these methods are based on a very simplistic view of the unconscious mind and, whether they are effective or not it, it is questionable whether they involve hypnosis as I have described it here in terms of suggestion and suggestibility.

Other methods are more directly based on suggestion. The therapist uses suggestions to bring about beneficial changes in the way the patient is behaving, thinking and feeling.

(Concerning the last point, it's worth mentioning that now and again the media run sensational stories about patients undergoing major surgery using self-hypnosis with no anaesthetic. There are various ways of using hypnosis to alleviate or manage pain but I am not altogether sure that hypnosis is the medium through which these dramatic cases of anaesthesia are effected. There have similar reports of the use of other methods (e.g. 'noesitherapy' due to the Spanish surgeon Dr. Angel Escudero) that do not seem to involve hypnosis or direct suggestion. It appears that certain people in certain situations are able to 'decide' that they are not going to feel any pain and they don't. It is unclear if this involves suggestion in the way it is understood here.)


Let us now sum up the main points of this paper.

  1. The term 'hypnosis' denotes an interaction between one person, the 'hypnotist', and another person or people, the 'subject' or 'subjects'. In this interaction the hypnotist attempts to influence the subjects' perceptions, feelings, thinking and behaviour by asking them to concentrate on ideas and images that may evoke the intended effects.

  2. The subject's experience and response are intended to have a realistic` and an automatic or effortless quality.

  3. Despite this, it is best to think of hypnosis as something that the subject does. Different subjects may employ different skills at their disposal in their endeavours to achieve the effects suggested by the hypnotist. However, it is those individuals who are able to experience the intended effects as realistic and involuntary who are traditionally regarded as being 'good hypnotic subjects'.

  4. People vary in their degree of suggestibility, which can be reliably measured by suggestibility scales. A person's suggestibility score is a very consistent over the course of his or her lifetime.

  5. It is customary when administering hypnotic suggestions to first carry out hypnotic induction and deepening procedures. Traditionally these consist of suggestions that encourage the subject to narrow his or her attention onto just one stimulus, image or idea, and to become relaxed, tired, drowsy and sleepy.

  6. The role of the induction has traditionally been conceived of as placing the subjects in an altered state of consciousness of 'trance', one property of which is enhanced suggestibility. However, research has shown that, for the majority of subjects at least, there is no convincing evidence of a unique trance state. Gains in suggestibility are observed following a hypnotic induction for a proportion of subjects but these appear to be due to enhanced commitment, motivation and expectation. Any induction method that achieves this can be used, even without reference to mental and physical relaxation.

  7. The concept of trance however may be retained to denote, as in the everyday use of the term, a state of inner absorption. It may be desirable for a patient to experience this in some clinical applications and the traditional induction methods may be usefully applied in such cases.

  8. Because of certain unusual characteristics, it may be that a small number of subjects do experience an altered state of consciousness, at least when undergoing traditional hypnotic induction procedures.

  9. EEG, brain-imaging procedures, and neuropsychological testing have revealed differences between groups of individuals of high, medium and low suggestibility while they are responding to suggestions or performing other tasks both during and outside of hypnosis. This evidence indicates that the responsive subjects are having genuine experiences and are not merely complying or pretending.

  10. It is not the case that these studies indicate that subjects are in a unique state of consciousness when undergoing hypnotic procedures. Also, despite these findings, it remains the case that the expectations and demands generated by the context in which hypnosis is undertaken are major determinants of the subjects' experiences and behaviour and the way they interpret them.

  11. A plausible explanation of how responsive subjects are able to experience the suggested effects as involuntary and realistic is that they are able to exclude from awareness elements of their response that would normally be represented in consciousness. With some suggestions this may be the explicit representation of a stimulus itself, though the stimulus may still implicitly register behaviourally, cognitively and emotionally in the usual way.

  12. Hypnosis does not have the property to cause people to do things against their will. It does not improve people's ability to remember events or information any better than similar procedures that involve relaxation and imagination. Other than the general effects of increased motivation and expectation, of itself it does not improve one's abilities and skills. Hypnotic subjects are not compelled to tell the truth. There is little evidence to support the claim that hypnosis acts on, or allows access to, 'the unconscious mind'.

  13. Clinical trials of hypnotic treatments include many of poor quality but the outcome is often superior to no treatment or placebo. Treatment is often very similar to 'non-hypnotic' procedures using relaxation, imagery etc. and often includes other procedures that are not part of hypnosis. Except in the case of pain relief and in certain physical conditions, a successful outcome is often unrelated to the patient's suggestibility, indicating that the beneficial changes may not arise primarily through the medium of hypnotic suggestion.


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