When I think of hypnotism, I conjure up the image of some sleazy magician in a black tuxedo holding up a watch in front of someones face for a while and gaining "control" over them (or in the above image, shooting some sort of magic beams at a sleeping woman from the 1800's). The magician then goes on to make suggestions for silly actions for the participant to do and the participant, (faking) of course, plays along.
However hypnotism isn't just a fake parlor trick. It's a real thing, a part of our natural sleep cycle, people actually can be hypnotized and really are more responsive to suggestions. [1] It's a technique which is effectively employed to help people deal with things like drug addiction, depression and pain. Hypnosis has even been shown to be useful in helping people deal with the side effects of cancer treatments.
However a new article published in the journal Nature: Scientific Reports titled "The Power of mind: Blocking visual perception by hypnosis" caught my eye. Blocking visual perception? With hypnosis?
Seriously? I had to read more.
The authors begin in their introduction discussing a few of the published examples of hypnotic phenomenon, one which they discuss is particularly interesting. It has been shown that participants can be hypnotized to have a color in their vision replaced with grey. (say instead of seeing red, when ever they are shown red they will see grey instead). [5]
Which means that the way your brain processes information can actually be affected by suggestions made while in the sleep/hypnotic state. Mind..Blown!
Here they wanted to take things a step further and try to see if they could remove peoples perceptions of Something altogether. Not only that, they wanted to monitor their brains directly while they did it (this is science after all, and what scientist doesn't love a good brain monitoring session!).
Well... they hypnotized some participants (and some they didn't, the non hypnotized were the control participants) and then suggested that they see a wooden board in front of them, which blocks their view of a computer monitor. Participants were first grouped into three categories based on how susceptible they were to being hypnotized using the "Harvard Group Scale For Hypnotic Susceptibility." [8] These groups were just called low, medium and high based on that susceptibility rating.
Then the participants were hypnotized (or not) as discussed above. During the next part of the experiment the participants were required to keep their eyes open and watch for some "stimuli" to flash up on the computer monitor. They were tasked with keeping count of how many times a circle or square flashed on the screen among a whole bunch of triangles flashing on the screen (IE they were trying to pick out how many times a rare visual was there.. and remember they were hypnotized to think they have a board in front of their face.. which would make this difficult).
During this process the participants were having their brains monitored by electroencephalogram (EEG) so the researchers could see if there were differences between the hypnotized and the control participants. They also tallied up the participants answers as to how many of the rare shapes they saw.
The article begins with a plot showing how well the participants did at seeing the shapes correctly:
This figure is looking at people who were not hypnotized (control) divided into the three groupings as to how susceptible they were to being hypnotized (even though they were not), and we can see they all did pretty well.
To the right we see the hypnotized group did a bit worse for those who were classified as low and medium susceptible to being hypnotized, while the group which was most susceptible did pretty bad only seeing 60% of the shapes (that damn board was in the way I swear!!). The difficulty that this highly susceptible group was statistically significant (p < 0.001), and indicates that they were truly having difficulties seeing as a result of the hypnotic board.
If you recall, the authors were also monitoring the participants brain activity EEG during the test. What we are looking at here is a map of the average of either control participants or hypnotized participants, where the authors have plotted the size of the electrical impulses of their brains in response to the shapes they were looking for on the screens. What you can see is that the hypnotized group had much smaller sized electrical responses in their brains when looking for the shapes. They report that this decrease is also statistically significantly related to the difficulties in counting the shapes for the hypnosis group (p < 0.001)
I think this is pretty wild!
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