Head Hacking – Free Your Mind Part 2 – Here Comes The Science

This is the second part of the Free Your Mind article about our work at Head Hacking Research. In the first part, I introduced some definitions of hypnosis, and we looked at some of the most popular models of hypnosis that working hypnotists ascribe to.

In this part, I will describe some of the important scientific discoveries about hypnosis by looking at some of the more popular academic models of how hypnosis works. Please read part 1 first to understand the context in which this article was written; it also provides a reference to The Oxford Handbook of Hypnosis that you should consider looking into.

Hypnosis Scales

Many hypnotists have heard of the Standford Hypnotic Susceptibility Scale Form C (SHSS:C – Weitzenhoffer and Hilgard original, Kihlstrom modified version) but I doubt few, outside of academia, have spent time understanding what it is and how it is used.

It has often been referred to as the ‘gold standard’ of hypnosis scales, with high reliability across the population and over time; subjects have been retested after 25 years and their scores were found to be reliably consistent with their original scores (Piccione, Hilgard and Zimbardo, 1989).

The SHSS:C was designed as a means of measuring the hypnotisability of a subject; it consists of an eye-closure induction, followed by deepening and 12 scoring tests ranging from easy (arm drop) to difficult (hallucinated voice). Subjects score 1 point for each test passed and these are totaled to provide their overall score.

While it is commonplace to refer to an arm drop suggestion as ‘easy’ and a hallucinated voice suggestion as ‘difficult’, in reality these could easily be described as ‘common’ and ‘rare’ instead; there is little to suggest that the hallucinated voice suggestion is at all difficult for a subject capable of it, but capable subjects do seem to be relatively rare.

Instead, the notion of suggestions being easy or difficult rides with the hypnotist rather than the subject, with the perceived ease of achieving responses to them being determined by how often they achieve them. i.e. suggestions that are only responded to on rare occasions are considered more difficult by the hypnotist than suggestions that get responses most of the time, but this has nothing to do with the difficulty that the subject experiences when taking the suggestion.

Importantly, the rarer suggestions are in fact no more difficult for the hypnotist; it’s just that subjects capable of them are less common. It is literally just as easy to suggest “I am invisible” as it is to suggest “Your arm is heavy”; if you haven’t tried it, do it. You might be suggesting it to a capable subject, and the results will be amazing.

Back to the SHSS:C. If you were to take a random sample of the population and deliver the SHSS:C to them individually as prescribed, then you would be very likely to obtain results that followed the normal distribution, otherwise known as a bell curve. This is a curve on a graph where a small number of people achieve low scores, the majority score somewhere around the middle, and a few score high scores.

The reason you would expect the normal distribution is because multiple experiments using the SHSS:C around the world have resulted in just that with sufficiently high consistency between them to suggest that the general population would respond with a very similar normal distribution to these.

If your group is a random sample then it is reasonable to assume that this group would also follow the normal distribution too (in fact it is more than reasonable, the range of deviation of each sampled group from the most average group also follows the normal distribution, allowing us to know how different our group would need to be for us to think that something had affected the results. See Experiment, Design and Statistics in Psychology by Robson for more information on normal distributions and standard deviations).

The results for the SHSS:C show that approximately 10% of the population achieve low scores in the range of 0 to 2; 80% achieve medium scores in the range of 3 to 8; and 10% achieve high scores of 9 to 12.

As a general rule of thumb, subjects who score low only achieve ideomotor suggestions; subjects who score in the medium range achieve ideomotor and challenge suggestions with some achieving some cognitive suggestions; and subjects who score high tend to be able to achieve the majority of the phenomena. A range of other scales also exist with similar items, some being shorter and others being designed for group situations. All of the scales in use have produced results consistent with the SHSS:C.

A range of clinical scales of ‘depth’ also exist which are generally given during clinical settings rather than laboratory settings; these too are consistent with the academic scales. It is fair to say that the various academic approaches to testing the capabilities of subjects are at least consistent.

If they are wrong, in that they are incorrectly measuring hypnotic capabilities, then the majority of hypnosis academics in the various laboratories have not spotted the error and given that a number of these also provide clinical hypnosis as part of a therapy programme, it would be unfair to claim that the academics approach hypnosis differently to hypnotherapists as many of them are also hypnotherapists too.

I hope that all hypnotherapists care about ‘what works’ – I think the difference is that the academics want to use reliable data and statistical methods to determine ‘what works consistently’ and I think they are right to do so.

There is a problem with the SHSS:C however. By title, it measures hypnotic susceptibility, which has long been assumed to be a synonym for hypnotisability. Since the early days of hypnosis, it was assumed that an induction was necessary to create a hypnotic state in which suggestions could be given. Waking hypnosis (i.e. without an established hypnotic state) was generally seen as producing only the ideomotor phenomena and that a hypnotic state was required to produce challenge or cognitive phenomena.

We know from Hypnosis Without Trance and our own Permanosis that the full range of suggestions can be given without an induction, but this wasn’t the prevailing view when the scales were developed in the 1950s and 1960s.

The problem was that by assuming that an induction was necessary, no one had tested to see if the subjects would take the suggestions anyway. Kirsch reports on experiments where the SHSS:C scoring suggestions were given to subjects who had not been hypnotized (Kirsch, 2008) and shows that the induction makes very little difference to the scores. He suggests that such scales should be referred to as measures of response to suggestion rather than measures of hypnotic susceptibility or hypnotisability.

There has been debate about whether subjects respond in the same way when given suggestions without an induction as they do when hypnotized (following an induction). A paper by Raz et al (Raz et al, 2006) shows that ‘highs’ (subjects that score 9-12 on SHSS:C) can act on a suggestion that suppresses the Stroop effect without an induction.

An example of the Stroop effect can be seen when naming the ink color that a word has been printed in; ‘color’ words (‘red’, ‘blue’, etc) printed in the same ink color as the word can be identified quicker than neutral words (‘work’, ‘drive’, etc), and these can be identified quicker than ‘color’ words printed in mismatching colored inks. Suppressing the Stroop effect means to decrease performance on congruently colored words (‘red’ printed in red ink) and to increase performance on incongruently colored words (‘red’ printed in blue ink).

Due to the nature of the tests, it is believed that the subjects cannot fake response to this suggestion, or in any way otherwise willingly improve their incongruent word performance, and that they are therefore (at least functionally) acting upon the suggestion in the same way as the hypnotized subjects (as both must be responding to the suggestion and not simply complying). We could assume that suggestions given without an induction can be taken just as readily and in the same manner as suggestions given following an induction.

There is another problem with the SHSS:C and that is that it only records behavioral responses, or the overt actions of the subjects. As I outlined in Part 1, only the subject knows whether they were responding to the suggestions or whether they were acting.

The underlying assumption was that behavioral responses correlate with the subjective sensations, that if a subject raises their hand in response to a suggestion then this must have occurred non-volitionally. Spanos et al (Spanos et al, 1983) demonstrated that this was not the case with a study involving the Carleton University Responsiveness to Suggestion Scale (CURSS).

The CURSS scores responses to suggestions on three dimensions: the objective score (CURSS:O) that records a point for each suggestion for which the subject makes the appropriate behavioral response; the subjective score (CURSS:S) that records between 0 and 3 points for each suggestion, depending on how much the subject experienced the appropriate sensations, from “Not at all” to “A great deal”; and the objective-involuntariness score (CURSS:OI) that records between 0 and 3 points for each suggestion that was experienced as involuntary to some degree, ignoring those suggestions that did not elicit a behavioral response or a sense of involuntariness.

Spanos et al showed that behavioral scores were substantially higher than objective-involuntariness scores, implying that scales that only measure the behavioral response, such as the SHSS:C, systematically over-estimate the response to suggestion.

Hypnosis scales are important in academia but are probably irrelevant to the work of the average hypnotist. What we can take from them are the expected results from hypnotizing random members of the public.

For example, Kirsch et al (Kirsch et al, 1995) showed that approximately 25% of college students achieved suggested amnesia; this is quite useful if we plan to use hypnotic amnesia as part of a performance as we could assume that for every 4 people that we test, only one will achieve the amnesia suggestions.

We can also benefit by incorporating their evolved pre-talk or introduction. A handful can be obtained from http://www.hypnosisandsuggestion.org/scales.html and from John Kihlstrom’s website, http://socrates.berkeley.edu/~kihlstrm/hypnosis_research.htm – they are worth reading as they have been tuned to make subjects as cooperative and at ease as possible.

Neodissociation Theories

Ernest Hilgard developed neodissociation theory (Lynn and Rhue, 1994) which is based on the concept that hypnosis causes consciousness to be divided into parallel streams of processing that are separated by an amnesic barrier; a ‘hidden observer’ would remain present which could later be interrogated to reveal information that the subject has post-hypnotic amnesia for.

Hilgard’s descriptions of neodissociation theory had sufficient latitude for Kenneth Bowers to define an alternative version of neodissociation theory, known as dissociated control theory (Woody and Sadler, 2008). More recently, Erik Woody and Pamela Sadler (2008) have integrated the two theories into a framework that could support either one exclusively or a combination of both theories.

Hilgard’s neodissociation theory suggests that when subjects take a simple suggestion, their stream of consciousness is divided into two streams of consciousness. One stream of consciousness produces the behavior required by the suggestion knowingly and the other stream of consciousness, that is on the other side of an amnesic barrier, observes the effect as happening involuntarily, with no knowledge that the other stream is actually producing the behavior.

The stream of consciousness that produces the behavior is aware that it has done so and can be quizzed by a hypnotist by simply suggesting that the ‘hidden observer’ will answer. Hilgard produced evidence for the existence of the hidden observer, and used this to support his theory of multiple streams of consciousness, separated by amnesic barriers.

Nicholas Spanos attacked the hidden observer and concluded (Spanos and Coe, 1991, quoted in Kirsch and Lynn, 1998) that “reports of experiencing a hidden part and ratings of hidden pain reflect the construals that people develop from the instructions used in hidden-observer experiments.” This means that the existence and character of the hidden observer could be dictated in the instructions given to subjects in the pre-talk.

Over a series of experiments, Spanos demonstrated that the hidden observer’s presence depended on the instructions given by the hypnotist – give one set of instructions and a hidden observer is present. Give a different set and there isn’t one.

He also showed that the hidden observer’s reports could be influenced by the instructions given – tell them the hidden observer sees a mirrored view of the world (due to brain-vision cross-wiring), show them the number 81, give them amnesia for it, ask the hidden observer what they saw and they will report the number 18.

Further he showed that he could create multiple hidden observers (each amnesic of each other), and therefore supposedly multiple streams of consciousness and multiple amnesic barriers, through variations in the instructions.

The simple conclusion is that the hidden observer is the result of suggestion and is therefore not part of the mechanism of hypnosis, but part of the effect.

Kenneth Bowers attacked the amnesic barriers by pointing out that suggested amnesia was a relatively rare occurrence (25% of subjects achieving it), yet it was being used implicitly to provide the mechanism that allowed the more common ideomotor and challenge suggestions to be achieved.

Instead he favoured his model of dissociated control that claimed that in hypnosis, suggestions can be accepted by subsystems of control below that of executive control without the awareness of this executive. It implies that suggestions bypass the executive control (the central decision making entity) and act directly on the parts of the brain that cause things to happen (the subsystems of control) by dissociation between the executive control and these subsystems.

What Bowers’ theory fails to explain is the physiological mechanism that permits the dissociation and also the granularity of selection in how the dissociation manifests. For example, some suggestions are taken and others are not and differences can be seen within the same subject on different occasions – why are there these differences in which dissociation’s are possible on different occasions?

Another example would be selective amnesia; a subject can be amnesic for very selective information (their name, for instance) but have access to other memories as normal. A mechanism of dissociated control would need to be flexible enough to cope with very specific dissociation on some occasions and very broad ones on others.

In addition to these questions, Kirsch and Lynn do a thorough job (Kirsch and Lynn, 1998) concluding, “The evidence supporting either version of dissociation theory is slim, and both are beset with serious conceptual difficulties.”

Woody and Sadler (Woody and Sadler, 2008) propose an integrated framework that supports dissociated control theory and a revised version of neodissociation theory, known as dissociated experience theory. Dissociated experience theory suggests a dissociation between the executive control and the executive monitor, which is the part that observes the current situation. In this version of the theory, the executive control acts out the suggestion but the executive monitor is unaware that it is doing so, thereby causing the subject to experience the effect as involuntary.

While this simplified version of neodissociation theory (lacking the amnesic barriers, hidden observers and streams of consciousness) stands up to much of the previous criticism, it doesn’t provide a mechanism for causing the dissociation and therefore does not explain why some suggestions are taken and others are not.

It also still suggests a form of amnesia as the effect of the dissociation, falling to Bowers’ original criticism of neodissociation theory, that explaining the occurrence of common suggestions (ideomotor and challenge suggestions) through the use of a rarely displayed occurrence (suggested amnesia) is contradictory.

Social Cognitive Theories

If neodissociation theories don’t stand up or tell the whole story, then what are the alternatives? The main ones are social cognitive theories; these are theories of hypnosis that assume that hypnotic behavior is, in fact, normal behavior that is interpreted as being hypnotic, due to the social context and the resultant, elicited cognitive strategies.

The social cognitive arena is quite broad and represents a number of viewpoints, but it can often be too easily (and wrongly) generalized to represent only “social compliance” theories of hypnosis, the over-simplification that the subject is only ever playing along and is always entirely in control of their own behavior. By generalizing in this way and dismissing the “social compliance” answer, it is possible to (wrongly) dismiss the whole social cognitive arena and miss out on the fascinating evidence and insights that it has to offer.

Graham Wagstaff proposed that subjects enlist cognitive strategies in an attempt to achieve the suggested phenomena with the sense of hypnotic involuntariness, and in some cases succeed, but when they fail they would often fall back on simply complying with the suggestion without the hypnotic sensations, in order to meet the demands of the social context.

There are two key ideas: the first is that successful hypnotic responding involves cognitive strategies and only accounts for the highly hypnotisable subjects; the second is that the majority of the moderate and low hypnotisable subjects (and potentially a proportion of the highly hypnotisable subjects) are playing along, pretending to be hypnotized and pretending to accept the suggestions.

There is an argument that is often levied (wrongly) at stage hypnosis by some hypnotherapists, often as part of their marketing literature, that subjects on stage in a hypnosis show are natural show-offs that want to act in outrageous ways. The equal and opposite argument is also often made, that the shy person who ends up on stage actually secretly wants to do outrageous things and that stage hypnosis provides the acceptable context within which to do so, without having to take responsibility for their actions.

These could both be true, accounting for different subjects with different natural personalities and different responses to the context, but for the fact that no one can act as well as a hypnotized subject, especially without acting lessons or any acting experience. Hardly any subjects that appear on stage at hypnosis shows have any acting abilities in their normal life, but somehow they magically manage to instantly turn out excellent performances when vague, improvised scenarios are sprung upon them.

What we should take away from Wagstaff is that the people on stage are probably the highly hypnotisable subjects who naturally manage to experience the suggestions in an involuntary way, because if they were not, then their acting abilities would let them down as they attempted to comply in order to show-off. With these subjects, the suggested scenarios are perceived as real and their behavior is not an act, but their natural response to what they perceive to be reality.

Unfortunately, if we are to accept the social compliance argument then we have to accept that most of the people who visit a hypnotherapist will end up complying, or pretending, rather than actually being hypnotized and acting upon the suggestions in an automatic fashion.

There are other social cognitive views, however, and they provide more hopeful and promising evidence. Donald Gorassini and Nicholas Spanos (Gorassini and Spanos, 1986) proposed that successful response to suggestion was due to a skill and that the skill could be acquired.

They developed a 75 minute training course, the Carleton Skills Training Package (CSTP), that involved three key components: the first was being given information aimed at removing misconceptions and improving attitudes to hypnosis; the second was watching a video of a highly hypnotisable subject being hypnotized and successfully acting upon suggestions – the subject narrated their thoughts during the hypnosis session and was interviewed about it afterwards; the third was practicing acting like a highly hypnotisable subject in pretend hypnosis sessions.

Gorassini and Spanos randomly allocated low and medium responding subjects to four groups. All subjects were scaled for response with the CURSS. One group was then given the CSTP hypnosis training, two groups were given different partial versions of the CSTP training, and the final group, the control, was given a personality questionnaire to fill in (to consume the same amount of time). All groups were then scaled with the CURSS again and a version of the SHSS:C, modified to include subjective and objective-involuntariness scores.

In the group that was given the full CSTP, half of the originally low responding subjects and 80% of the original moderates, responded as highly hypnotisable subjects when rescaled after the hypnotic training. The control group showed no change and the partial groups showed partial improvements. In 75 minutes, Gorassini and Spanos had changed how the subjects responded to hypnosis; not only that, but the subjects retained their new scores when retested later and the effect appeared to be permanent.

Gorassini went on to develop a shorter hypnotic training course (Gorassini, 2003) that took only 4 minutes. It actually involved a 2 minute script: the subject was given a transcript to read while listening to it being read on tape; they were then given a further 2 minutes to read the transcript again, totalling 4 minutes. Still, with only 4 minutes of training, subjects improved their response as measured on a standard scale.

Modification of response to suggestion has been criticized, however, for only causing behavioral responses without the sense of involuntariness (Bates and Brigham, 1990); in other words, the subjects learn to act like good subjects but do not actually become good subjects.

Still, other studies have confirmed that the subjects significantly improve on their subjective ratings of involuntariness, even if the effects are not as pronounced as Gorassini and Spanos originally reported (Gearan, Schoenberger and Kirsch, 1995; Cangas and Pérez, 1998).

Modification techniques have extended to working successfully with subjects with zero response to suggestion (Cangas Díaz and Pérez Alvarez, 1998). A study testing a ten minute brief training, however, failed to find any significant improvements in response to suggestion and specifically for the effect of analgesia (Milling, Kirsch and Burgess, 1999).

Overall, the evidence suggests that response to suggestion is modifiable through training, even if it is not fully understood what the training needs to include and how it needs to be delivered. The fact it works, however, has ramifications for all hypnotists. If it is possible to condense the training into something that approximates a pre-talk or introduction, then we could improve all of our subjects before we even attempt to hypnotize them, thus significantly raising our success rates.

More importantly, however, it indicates that what the subjects do when they are given a suggestion matters; if they engage in the right cognitive strategies then they are more likely to succeed at taking suggestions. These cognitive strategies appear to result in subjects experiencing the effects of the suggestions with the sensation of involuntariness.

At this point, it is worth remembering that response to suggestion is not dependent on an induction and that a trance may be the effect of the induction suggestion, rather than a special state or process. The social cognitive theories have resulted in brief training courses that modify subjects’ abilities to respond to suggestion in a manner that feels involuntary.

The evidence points towards cognitive strategies being the mechanism of hypnosis, with the experience or appearance of dissociation being an effect rather than a cause. With that in mind we approach a key social cognitive theory from our heroes, Irving Kirsch and Stephen Jay Lynn.

Response Set Theory

Remember back in Part 1, I told you that we had no free will. Well that actually has further implications for models of hypnosis. If we do indeed have no free will, as the neuroscience suggests, then everything we do is automatic and therefore involuntary. Response to suggestion is no different, it is just as automatic and involuntary as all of our other normal actions. The difference, as I highlighted in Part 1, is that response to suggestion is accompanied with a sense of involuntariness.

If everything we do is involuntary, then normally we must (automatically) ascribe an illusion of intention to our actions; this causes us to believe that we intended to cause our actions, supporting our illusion of free will. Response to suggestion, on the other hand, removes this illusion of intention and leaves us with the reality; we become aware of the true, involuntary nature of the behavior associated with acting on the suggestion, while preserving the illusion for all our other behavior.

That’s probably worth reiterating: in normal life our actions are automatic but we perceive them as being voluntary and intentional; when we respond to suggestions, this perception is removed for the associated behavior and we get to observe it without the artificial sense of intention we would normally feel if we perceived that we were acting ordinarily and voluntarily.

This viewpoint was suggested by Irving Kirsch and Stephen Jay Lynn (Kirsch and Lynn, 1997) as part of their Response Set Theory. The theory suggests that in all waking moments, we elicit appropriate behavior (response sets) in response to stimuli, then act, and then ascribe intention to our actions.

For subjects that respond to suggestion, the hypnotic context provides the stimulus for the hypnotic response set; this includes acting on the suggestions and experiencing the effects as happening automatically. For subjects that do not respond to suggestion, the elicited response sets do not result in a hypnotic experience.

Kirsch and Lynn’s approach to researching response set theory could be characterized as the search for the personality traits or cognitive strategies that are associated with good subjects and therefore good response sets for hypnosis. They have identified that the subjects’ expectation of their response to suggestion, particularly after they have been given a suggestion and had a chance to act upon it, is correlated with their actual response.

Experiments where the researchers gave suggestions that the subjects’ vision would slowly change color, while also (secretly) simultaneously slowly changing the color of the room lighting in sympathy (providing the effect that the subject was experiencing the effects of the suggestion automatically), had the effect of increasing the subjects’ expectations of responding to suggestions and therefore also increasing their actual response to suggestion (discussed in Kirsch, 1985).

It has been shown that the personality traits of absorption, fantasy proneness and dissociation are not indicators of response to suggestion, while expectation and attitudes towards hypnosis are to a degree (Kirsch, Comey and Reed, 1995).

Response set theory, while embracing the illusion of free will, fails to fully explain what leads to good response sets for responding to suggestion and how those response sets remove the veil of ascribed intention to lay the automatic processes bare for us to become aware of. It does, however, provide a simple and grounded model from which to explore and answer these questions.

Summary of The Science

Hypnotic scales are reliable and consistent although not directly applicable to working hypnotists. They can, however, be a useful source of data and the pre-talks are good. Dissociation theories suggest that one bit of our brain become less aware of another bit when acting upon suggestion; these theories generally suffer from conceptual problems.

Social cognitive theories suggest that cognitive processes are key to successful response to suggestion but suffer from failing to fully identify what those processes actually are. Response set theory highlights that response to suggestion removes the illusion of intention over our actions rather than adding the illusion of involuntariness, but fails to fully specify how this occurs.

In part 1, I discussed popular models of hypnosis and in part 3, I’ll introduce The Automatic Imagination Model.

Please have a look at our free videos at youtube.com/theheadhacker and youtube.com/how2hypnotisetwitter.com/headhackinglive

In addition, don’t forgot to also check out the contest we’re currently throwing right here on Whats On My Brain! All you have to do is click the following link to find out how to enter: The Ultimate Head Hacking Contest/Giveaway

Kev Sheldrake, Hypnotist
Head Hacking

References

Hypnosis scales – http://socrates.berkeley.edu/~kihlstrm/hypnosis_research.htm
1983, Nicholas Spanos, H. Lorraine Radtke, David C. Hodgins, Lorne D. Bertrand, Hernerikus J. Stam & Debora L. Dubreuil, The Carleton University Responsiveness to Suggestion Scale: Stability, Reliability, and Relationships with Expectancy and “Hypnotic Experiences”
1985, Irving Kirsch, Response expectancy as a determinant of experience and behavior
1986, Donald Gorassini and Nicholas Spanos, A Social-Cognitive Skills Approach to the Successful Modification of Hypnotic Susceptibility
1989, Carlo Piccione, Ernest R. Hilgard, Philip G. Zimbardo, On the Degree of Stability of Measured Hypnotizability Over a 25-Year Period
1990, Brad L. Bates and Thomas A. Brigham, Modifying hypnotizability with the carleton skills training program: A partial replication and analysis of components
1991, Nicholas Spanos and William Coe, A social-psychological approach to hypnosis
1994, Stephen Jay Lynn and Judith W. Rhue, Dissociation: Clinical, theoretical and research perspectives
1995, Paul Gearan, Nancy E. Schoenberger and Irving Kirsch, Modifying Hypnotizability: A New Component Analysis
1995, Irving Kirsch, Christopher E. Silva, Gail Comey and Steven Reed, A spectral analysis of cognitive and personality variables in hypnosis: Empirical disconfirmation of the two-factor model of hypnotic responding
1997, Irving Kirsch and Stephen Jay Lynn, Hypnotic involuntariness and the automaticity of everyday life
1998, Adolfo J. Cangas and Marino Pérez, The effect of two procedures on hypnotic susceptibility modification
1998, Adolfo Cangas Díaz & Marino Pérez Alvarez, Transformation of instructions into suggestions using operant procedures
1998, Irving Kirsch and Stephen Jay Lynn, Dissociation Theories of Hypnosis
1999, Leonard S. Milling, Irving Kirsch and Cheryl A. Burgess, Brief modification of suggestibility and hypnotic analgesia: Too good to be true?
2003, Donald Gorassini, Brief Hypnotic Suggestibility Training
2006, Amir Raz, Irving Kirsch, Jessica Pollard, and Yael Nitkin-Kaner, Suggestion Reduces the Stroop Effect
2008, Prof Irving Kirsch, Suggestibility or Hypnosis – What do our Scales Really Measure?
2008, Erik Z. Woody and Pamela Sadler, Dissociation theories of hypnosis (in Nash and Barnier, Oxford Handbook of Hypnosis)