Interview with Dr. Peter Suedfeld: The Science of Sensory Deprivation Therapy


I am really excited to share with you my first journalistic piece for Discover Magazine's big ideas blog – The Crux.

Contrary to popular belief, sensory deprivation (aka Restricted Environmental Stimulation Therapy, or REST) in a controlled setting is not inherently unpleasant. In fact, according to over three decades of research, a few sessions of REST may boost creativity, alleviate chronic pain and reduce stress and anxiety. These days you can try it yourself: many commercial "float houses" offer flotation REST, where you float in a light- and sound-proof tank with skin temperature salt water to minimize sensation.

Two weeks ago I hopped into a sensory deprivation tank to see what the fuss was about. Along the way, I interviewed Dr. Peter Suedfeld, one of the pioneering researchers looking at REST, and experienced musical hallucinations for the first time in my life. For the full story head over to The Crux and check it out!

There's a lot of interesting material that didn't make it into the article. During my interview with Dr. Suedfeld we talked about the history of REST research and aspects of experimental design (control groups, placebo), which I think is very important when assessing the data critically. Below is the transcript of the interview, slightly edited for clarity.

REST was previously thought to be highly aversive. What prompted you to start studying it's therapeutic potential? Was there any pushback from the psychology research community?

It was considered aversive primarily because of the earliest research results, from McGill University and others, which reported cognitive decrements, hallucinations, mood swings, anxiety attacks, etc. In my own first studies, we found that these were actually due to the anxiety induced in the participants by an experimental artifact: the way in which they were made to feel before they ever entered the environment. Routinely, they were asked to sign a legal release form to hold the researchers immune from lawsuits in case the participant suffered psychological damage; there was a "panic button" if they wanted immediate release; they were not familiarized with the environment before being put into it; and so on. When I replaced those procedures with reassuring information, no release form, no panic button (they could just get off the bed and walk out if they wanted to), and complete tour of the REST chamber, all of those "symptoms" disappeared.   In addition, the original McGill situation and some others used sensory overload -- constant noise and white light -- rather than "deprivation". What they deprived people of was patterned perception, not sensory stimulation. Later studies showed that overstimulation was much more unpleasant than understimulation.

As to the torture allegation, that was due to two misunderstandings. One was the belief that UN prisoners in the Korean War were "brainwashed" with the use of sensory deprivation (as it was then called). This was untrue; when the facts were known, it turned out they were bombarded with overstimulation -- loud group harangues, beatings and other physical tortures, cramped cells where their limbs ached, and so on. And they weren't brainwashed, either.

The second was the use of dark, silent rooms or hoods over the head for suspects by various police agencies. The former was primarily used in dictatorships as an interval between sessions of dazzling light, rapid-fire questioning, and torture or beatings, which were much more effective as a shock technique after a period of silence and relative peace; the latter were used, e.g., in Norther Ireland by the British, to prevent the prisoners from identifying who was pointing them out as IRA terrorists, who was interrogating them, where the next question or blow was coming from and when, and generally disorienting them. In neither case did it have anything to do with REST: in both cases, overstimulation was again the actual situation. Regrettably, many people didn't really think the evidence through and just leaped to the conclusion that reduced stimulation was the source of the problem. The resulting politicized hullabaloo really damaged the progress of research in the field; many researchers dropped their programs after having been publicly criticized, insulted, threatened, and even assaulted.

What prompted you to explore the use of REST for cognitive enhancement? 

Some of the early studies with which I was involved were aimed at exploring rote memory and recall of previously heard material. To our surprise, we found that these processes improved when the participant was in a REST chamber for 24 hrs. between the presentation and the recall test. That got me interested in checking out the effects on other cognitive functions.

It's possible that the reason for the memory gain is similar to that induced by sleep and meditation: i.e., consolidation of memory traces without subsequent input that could interfere with the process. But REST also has positive effects on other cognitive processes, which sleep and meditation usually don't. We did have a Zen master in our flotation tank once. He was there for the usual hour; when he came out, he said that his routine was to meditate for 4-5 hours daily, and the depth of the meditative state he attained in the hour in the tank was such as he only experienced a few times a year when he meditated in his usual room. So it may be that REST induces the same state, but much more quickly and without effort (most people have to learn to meditate, and some people never manage it).

Advances in neuroimaging techniques are allowing us to explore brain circuitry activation during meditative states. Is there a way to see what's happening in the brain during a REST session?

It shouldn't be impossible to do some kind of scan in a REST chamber, and perhaps even in the flotation tank. Some kind of waterproofing in the latter should be feasible to ingenious engineering minds. People have taken EEGs in both REST situations, after all, and I understand NASA is working on an fMRI apparatus that could be used in space. If it's small and portable, it could easily be used in the chamber.

What would you say is the most adequate control for flotation-REST? And why?

Are we talking about research, or about therapeutic applications?
If research, then the answer is: overall, spending the equivalent time in your normal daily activities. To study specific aspects of the float experience, lying down in a dark, quiet environment (controlling for effects of flotation -- water, Epsom salts -- itself); floating with lights on and conversation (controlling for level of stimulation). If you want to compare effects, such as muscle relaxation or brain activity, use the standard situation for such measures: EEG, EMG, and so on, in the usual setting for those measures. If we're talking about therapy, the best control is the best known treatment other than REST for whatever condition you're thinking of applying it to. It's also useful to use placebos: depending on the condition being treated, an inert substance, an expectancy placebo group, an attention placebo group. I've used a number of control conditions myself, including a negative expectancy placebo group for smoking cessation (the participants were told that the chamber REST session was just a preparatory period of relaxation to get them ready for the actual treatment, not a treatment in itself).

What, in your opinion, is an adequate way to control for placebo effects? 

If you're trying for an actual therapeutic effect, use expectation too; whatever works is good, and we know from standard medical practice that expectancy and placebos can either reproduce or at least enhance the success of the actual treatment. For research, that is a problem, but if you have good control conditions, including some placebo group, the difference between those and the REST group tells you the effect of the latter.

Actually, in my first smoking cessation study, the eventual participants didn't know what it was about (no rules about informed consent in those days, but we could have got an exemption anyway). We recruited people for a (then) "sensory deprivation"(SD) study, chamber not flotation, and had volunteers fill out a background information form that asked -- among many other things -- whether they smoked, how often, how much, for how long, etc. We included only long-time, confirmed smokers in the study. The SD group was split in half, with some getting anti-smoking messages and the other getting no stimulation. The control group had the same two conditions.We found that SD had a significant impact on smoking reduction, regardless of the messages, and the control group had no change, again regardless of messages.

So it was pretty clear that a) there was no expectancy artifact accounting for the effect of SD, and b) SD itself did have an effect. When we collected the followup data, we phoned and told the subjects that we were doing a study on smoking behaviour; we didn't refer to the earlier SD study, and didn't mention any connection with it. Also, the people who made the phone calls had not been involved in the SD procedure, so their voices were not familiar to the subjects, and the answers were not confounded by the respondent wanting to please (or frustrate) the SD experimenters. That study led to a whole series of more applied studies, with very consistent results.

Do you think commercial float houses are capable of replicating stringent lab conditions and offer real benefits?

I think many actually offer REST experiences, not just REST-like ones. Some are very carefully designed and operated, pleasant and relaxing situations before going into the tank. I would be careful about going to them for some therapeutic purpose; some make claims that have no solid evidence, so I would check that out by searching the scientific literature (Google Scholar is pretty good on that). But if someone just wants a relaxing, restorative experience, they can be excellent.

Where do you see the REST research field going in the next few years?

There is a resurgence of the research, but so far to a great extent it's replications and extensions of work done in the1980's-'90s. There are labs in Scandinavia and the UK that are moving ahead with this. It's all flotation REST; I don't know of anyone using chambers, which is regrettable. They have very good effects that are different from those of the tank. My theory is that the chamber is more effective for processes under central nervous system control (cognition, habit change) and the tank for autonomic nervous system functions (muscle tension, aches and pains, relaxation, insomnia).