A Hypnotic Suggestion Can Generate True Hallucinations

13.08.2013

A group of researchers from the University of Turku, the University of Helsinki and the University of Skövde, Sweden has found evidence that hypnotic suggestion can modify the processing of a targeted stimulus before it reaches consciousness. In the experiments, they managed to hypnotically modulate the perception of colours of the subjects.

​The nature of hypnotically suggested changes in perception has been one of the main topics of controversy during the history of hypnosis. The major current theories of hypnosis hold that we always actively use our own imagination to bring about the effects of a suggestion. For example, the occurrence of visual hallucinations always requires the active use of goal directed imagery and can be experienced both with and without hypnosis.

- Our results challenge the previous theories since they indicate that all hypnotic responding can no longer be regarded merely as a goal directed mental imagery. We know that color experience is a highly automatic feature of perception, tells Docent Sakari Kallio from the University of Turku.

- In the research, we were able to create, with the help of hypnosis, a strong memory trace that activated before the participant was even aware of the shown sign.

Squares Are Always Red

One of the group's studies was done with two very highly hypnotizable participants. The researchers measured their brain’s oscillatory activity from the EEG in response to briefly displayed series of red or blue shapes (squares, triangles or circles). The participants were hypnotized and given a suggestion that certain shapes always have a certain color (e.g. all squares are always red).

One participant reported constantly experiencing a change in color immediately when a suggested shape appeared on the screen. This experience was accompanied with enhanced high-frequency brain activity (22 Hz) already 1/10 second (70-120ms) after the stimulus appeared and it was only seen in response to the shapes mentioned in the suggestion. The second participant did not experience the color change or the enhanced 22 Hz activity. However, she reported a peculiar feeling when a suggestion-relevant shape was presented.

- Sometimes I saw a shape that was red but my brain told me it had a different color.

This enhanced oscillatory brain activity is proposed to reflect an automatic comparison of input to memory representations.

- In this case, the hypnotic suggestion “all squares are red” led to a memory trace that was automatically activated when a square was presented. The matching must have occurred preconsciously because of the early timing of the effect and the immediacy of the color change, Kallio says.

Suggestion Has an Effect in the Waking Stage

For some, the hypnosis has an effect that makes them stiff and making conversation with them can be difficult.

- Importantly, our experiments were done by using a posthypnotic suggestion. The effect was suggested during hypnosis but the experience was suggested to occur after hypnosis. Thus all the experiments were carried out while participants were in their normal state of consciousness. They were also given a suggestion for not to remember the suggestions given to them, when they wake up, Kallio explains.

The research and results have important implications in psychology and cognitive neuroscience especially when studying visual perception, memory and consciousness.

The results are presented in two articles published in PLoS ONE and International Journal of Clinical and Experimental Hypnosis, 61(4): 1-17, 2013 (forthcoming).

HB
Photograph: Rachel Cobcroft

 

Created 13.08.2013 | Updated 13.08.2013