Types of Suggestion

To recap, a hypnotic induction produces a 'hypnotic trance' or a 'state of hypnosis', but most of the interesting things that happen in hypnosis are a result of suggestion.

Suggestions can be:

Deliberate vs. Unintentional

A deliberate suggestion might be something like "as you sit there you might notice that your arm is starting to feel lighter" (a suggestion for altered subjective experience).

Unintentional suggestions happen all the time. A well-known phenomenon in psychological reasearch is the Hawthorn Effect. This is the idea that people behave differently when they know they are being observed. "Observing people or making them feel special can be suggestive" (Michael, Garry & Kirsch, 2012). The placebo effect might also be thought of as an unintentional suggestion (although it is sometimes deliberate) - for example a patient might feel better if they take antibiotics for a viral infection, partly because they feel like something is being done for their illness.

Hypnotic vs. Non-hypnotic

A suggestion is hypnotic if it is delivered in the context of hypnosis. For example if it is delivered after a hypnotic induction, or if given at a time when the participant believes that they are hypnotised.

The same suggestions can also be delivered outside of hypnosis, to unhypnotised participants. In this context they are called non-hypnotic suggestions or imaginative suggestions. There is considerable research showing that hypnotic suggestions are only marginally more effective than imaginative suggestions.

Verbal vs. Non-verbal

Hypnosis and suggestion are classically thought of as verbal but there is a lot of research to show that suggestions can be delivered without words. In psychological research is is well known that the expectations of the experimenter can bias the result of a study (demand characteristics): this is why high-quality medical trials are 'double-blind' in order to try and minimise the effects of the expectations of the researchers and volunteers. There is also evidence that non-verbal, unintentional suggestions operate in different areas too. For example, in a study in which mock jurors were given instructions by a judge, their verdicts matched the private expectations of the judge (Hart, 1995).

Suggestion has impacts on many different domains

Suggestion operates in a wide range of areas, including:

Sensation & Perception

Suggestions can be given to affect what a participant sees, hears, or feels. For example, a suggestion might be be given to "hear the voice of a friend speaking to you", to "see a cat in your lap", to "feel the warmth of the sun on your hand", or to "feel like your arm is so heavy that you cannot lift it from your lap".

In one study participants were given a suggestion to see a greyscale picture in colour, or to see a colour picture in shades of grey.  Activity in the participant's visual cortex indicated that they really saw colour, even when it was not present in the real pictures (Mazzoni et al, 2009).

In another study participants had a heat-pad strapped to their hand. It was suggested that it would heat up to a painfully hot temperature when in fact it was turned off. Participants reported expeirencing pain, and this was accompanied by activity in 'pain areas' of their brain (Derbyshire, Whalley, Stenger & Oakley, 2004).

Implicit learning

In a study where the participant's task was to find a target amongst distractors (where the distractors subtly predicted the location of targets on some trials), participant's performance was affected by sniffing a scented pad. If participants were told the scented pad would improve their performance they performed faster, and they performed slower if given the opposite suggestion (Colaguiri, Livesey, & Harris, 2010).

Memory

Participants given a non-alcoholic drink and told it was vodka were more susceptible to misleading information. Participants given a placebo drink and told it was a performance-enhancing drug were less susceptible to the misleading information (Assefi & Harry, 2003; Clifasefi et al, 2007).

The effects of hypnotic suggestions upon memory have been widely investigated. A typical finding is that the quality of memory recall is not improved, but that the quantity or certainty of recall is increased.

Habitual or automatic responses

A well-validated finding in psychological research is that participants can name the ink colour in which a word is printed more quickly when it matches the colour named by the word (Stroop, 1935). This effect is thought to be automatic, and outside of conscious control. However, when highly suggestible participants are given a suggestion that to 'see clearly, but the words are gobbledegook (meaningless symbols)' then the Stroop effect is diminished (Raz & Campbell, 2009).

The effectiveness of medicines

In a study where participants were given a dose of muscle relaxant, they reported feeling relaxed if they were told it was a relaxant, and tense if they were told it was a stimulant (Flaten, Simonsen, & Olsen, 1999). 

In another study one group of hospital patients were administered the benzodiazepine diazepam without their knowledge, and another group were administered the drug and told that it was a powerful anti-aniety drug. Only the group who were told about the drug reported any reduction in anxiety (Benedetti et al, 2003).

A genuine response to suggestion

Faking

It is not possible to prove whether someone is genuinely hypnotised, or is genuinely responding to suggestion. For example, if a participant is given a suggestion that their hand is becoming lighter and is raising up in the air, then they might raise their hand because it genuinely feels lighter, or because they are faking. Similarly, if they are given a suggestion for pain relief they might report less pain because they feel less pain, or because they are trying to please. So how can we tell if a response to suggestion is genuine?

One way has been to perform tests that are difficult to fake. Raz and his colleagues used the Stroop test to show that responses to some suggestions take over automatic processes. Other ways include post-test debriefings where participants are given the opportunity to rate how 'genuine' or 'effortless' their responses were.

Involuntariness

One key characteristic of hypnotic responding is involuntariness. This has been called the "classic suggestion effect" (Weitzenhoffer, 1980). As a hypnotic suggestion is carried out by a subject, Weitzenhoffer argues that subjective experience should be that the behavior is happening all by itself, involuntarily. For example, if the suggestion is that the subject's arm is rigid like a bar of iron, the true hypnotic experience is that one's arm has really become rigid, on its own: the participant should not feel that they are deliberately holding their arm stiffly. Note that this involuntariness characteristic only applies to behaviours.

'Realness'

Tellegen (1978/1979) argued that a key criteria of a hypnotic response is how 'real' feels. For example, if a suggestion is given to experience being on a beach, then what matters is not how vivid the experiece is, but how real it feels - it must be experienced 'as real'.

 

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