Dr Peter Lush University of Sussex, UK

Dr Lush is a psychologist working on the role of hypnotic suggestion & people's experience & expectatations in studies of consciousness  

Dr Peter Lush had some ☕ at the error bar in episode 10 #fake #hand #RHI #body #hypnosis #suggestion

our discussion

welcome to the error bar. would you like to introduce yourself?

yeah, i'm Pete Lush. i'm a postdoc at the University of Sussex

great, welcome! it's great to have you here. can i get you a drink?

cup of tea

cup of tea! perfect

and a biscuit

biscuit for sure. so what brings you to the error bar?

um, you invited me!

that's a good point, because I, because I've overheard some lively discussions in the bar about the, the rubber hand illusion. maybe you can tell me a bit more about what that is?

yeah, sure, so the rubber hand illusion is an effect that was first written about 20 years ago now. you're sitting at a, at a desk, there's a box in front of you that you put your hand inside, so that you can't see it. you put your right hand inside there. there is a fake hand - a rubber hand - that would be placed away from where your hand is. you can't see your own hand, you can see a fake hand. the experimenter then takes two brushes and begins to stroke the fingers of your hand and the rubber hand, at the same time. this is usually referred to as the synchronous condition

so what you're seeing on the rubber hand is matching what you're feeling on your own hand. this is talked of as a multisensory illusion, and by multisensory it just means that there's two signals going on: you've got er vision - you can see the hand, the rubber hand - and you've got this tactile, this, this sense of touch - you can feel the stroking of the brush on the other hand

after this procedure people will then report an experience of touch felt on the rubber hand, rather than on their own hand, and an experience of ownership of the rubber hand. that's your, your basic set up. there is a control condition where the brushstrokes happen at different times. this is usually called the asynchronous condition

if it's going to be about this, this experience of ownership and touch transferred or referred to the fake hand, we need to ask people what their experience is, and the way that that's typically done is to give a set of statements that describe experience of the illusion. for the referral of touch this would be something like 'i felt the touch of the paintbrush on the rubber hand', and for ownership it would be the, er this, 'i felt as if the rubber hand were my hand'

there are other measures. the most popular of those is 'proprioceptive drift' - a measure of where participants perceive their own hidden hand to be before and after the rubber hand stroking. you might typically set up a ruler in front of you and ask you to point or to, to say where on this ruler you felt your hand was positioned before they start doing the rubber hand illusion procedure, and then afterwards they ask you again. and you'd see typically a shift in the direction of the rubber hand, a shift in the reported perception of the position of your own hand towards that of the rubber hand

and do different scientists agree on the best measurement of all these, or is there something that trumps the others?

i think it ultimately comes down to, if we're going to be measuring experience, everyone accepts that it has to be tied to report at some stage, the report of where you feel like your hand is. all this has built into a huge body of literature which claims to show us, i think it's seen as, it's been very very popular. there's this, this idea that this experience of body ownership, ownership of our bodies is so fundamental, the idea that it can be disrupted in this way, just through a very simple multisensory stimulus, for a very brief period of time, is really surprising, because it seems to tell us a lot about how our experience of body ownership comes about

it's exciting because it's an illusion and it's like you're gaining another body part or swapping someone else's body with yours?

yeah, but i think, i think that the key thing is that it's really exciting because, because it's really surprising right? it might be somewhat maladaptive to be so easily mistaken

because you can fall asleep on your hand, and wake up, and your hand's gone numb, you've had a temporary anaesthesia and it feels rubbery, dead, and it kind of feels like you've lost your hand a little bit. gaining another hand is, stranger

yeah, or if you imagine a situation, if we imagine a sort of, real life situation, you're sort of, you know, you're at a bar or something. the person standing next to you at the bar, their hand happens to be touched in the same way as yours at the time when you are standing there, you don't, i mean maybe people do - it's an interesting question - hang on, i mean is that my hand or is that my hand?

and do you feel the rubber hand illusion, have you had it?

erm, no. to be honest i'm not sure what the ownership question really means, i'm not sure how to interpret it, erm so i don't know if i've experienced that. the referred touch, the feeling of touch on the hand, that hasn't happened to me spontaneously, but i feel that with a sort of, effort of imagination, i could imagine as though the touch was on the rubber hand. i think i get some insight into the experience then, perhaps

i remember, back in my phd - a long time ago - i remember feeling it, and then not feeling it later on, and i've tried many times to get back in there, in the illusion, and it doesn't really work for me. so yeah, what is it that explains different people's susceptibility?

let's take a segue into, into another area of psychological research, and this is the history of, er, imaginative suggestion. it's been primarily studied within the context of hypnosis. the way that hypnosis is usually measured in the, in the laboratory is through scales, these standardised hypnotisability scales. these would typically be preceded by a hypnotic induction which can take virtually any form. usually in these scales it will be some sort of relaxation procedure, counting down, and being told that you're in a state of hypnosis. um, but a hypnotic induction can also be riding on an exercise bike, as long as you've been told that it's, er, hypnosis. it can be just 'now you are hypnotised'. it can be anything, pretty much, as long as it establishes that this situation is a hypnotic situation and things are going to happen. in other words, people's expectancies - what they're expecting to happen - is kind of primed, primed for something to take place

so people come to the experiment being more or less suggestible, more or less hypnotisable, they're sitting down at a table, with a rubber hand in front of them. so they have expectations about what they're going to feel - is that right?

yes. and, and the important point is that they will vary in their ability to meet those expectancies by generating some experience, by imagining something, but probably not being aware that they are, that that is what they're doing. it means that every time you run an experiment, you don't know whether they're the sort of person that reports nothing for all these imaginative suggestions, they don't experience any paralysis, they don't hear any mosquitoes, nothing. or whether they're somebody who gets all of it, and they're completely blown away by it, and it's like a life-changing experience for them, just sort of: 'wow, this is the most amazing!'

and i should say as well that there's a lot of evidence that there are changes in experience in imaginative suggestion. a hypnotic suggestion for analgesia, for example, people will repeatedly choose that other, over other forms of anaesthesia for dental surgery. if there's not any experience involved, you'd see, it would be quite a commitment to pleasing the experimenter or pleasing the dentist. you'd have to, you know, gritting your teeth, go: 'i'm going to pretend this is working'

so i think, i think probably here's a good place to talk about the concept of demand characteristics. this is a, a term that was introduced about sixty years ago by Martin Orne, who was a hypnosis researcher, it grew out of hypnosis research. he defined it as any aspect of the experimental situation, or any pre-existing beliefs of participants, that could affect expectancies, affect expectations in an experimental situation. he pointed out, or he argued, that, when you're studying humans, if you're running an experiment with humans and they turn up, we're not just blank slates, we don't just sit there absorbing, you know, or just performing the tasks that we've been instructed to do. we, we can't help ourselves, we're constantly trying to work out what's going on, it's an effort to stop yourself guessing what it is that you're supposed to be doing

Orne argued that, therefore, that what people expect in an experiment can bias the responses. some people might want to try and be a 'good participant' and give the experimenter what they believe the experiment wants. that is the key point that we're making when we talk about the rubber hand illusion, and when we talk about a range of other effects that we've been looking at as well. and this is that, what you expect in an experimental situation may lead to the generation of experience, by the same mechanisms as people respond to imaginative suggestion. so you expect a particular experience and you generate that experience

if you take a situation like the rubber hand illusion, some people will, they really seem to have had an experience, they're really wowed by it, it doesn't seem like they're putting it on, they go 'woah that was amazing!' but if you have run imaginative suggestion screenings, you get the same kind of responses. you get, there will be some people who are just really blown away: 'wow that was amazing!', 'how did you do that?', 'i could really, you know, it was like there was a mosquito walking on me!', 'i couldn't move my arm!'

if we return to the demand characteristics idea, we can think about what people might expect in the rubber hand illusion. you're sat there, you've got a rubber hand there, you've got your own hand. the experimenter starts to stroke your hand at the same time, what was that experimenter expecting to happen? people are going to be trying to work that out. if people can work out that they're expected to feel the touch over there on the fake hand, and if they can work out that they're supposed to feel like that hand was their own hand, then this could act like an implicit imaginative suggestion

hypnosis grew out of um, Mesmerism, it developed from Mesmerism, a sort of eighteenth century suggestion effect, which was attributed to the manipulation of magnetic fluid in the, in the air. at the time that was plausible enough scientifically. a hundred years later it wasn't so plausible and that's when hypnosis came along. in Mesmerism, typically there would be a sort of, something like waving hands over the body, or iron rods over the body. Mesmer used iron rods um at first, this was, you know they manipulated magnetic fluid, then he fell out with his iron rod maker, then he discovered he could do it with his hands... waving hands over the, over somebody, you don't tell them what they're going to experience, instead they just respond in some way. and there were people who had convulsions, or they would be cured of things, or you know, just this huge range of, there's a wide range - anything they could come up with, really, from that situation

so if i understand, your research that you've recently done shows that people are, they come into a rubber hand illusion experiment and they're, how suggestible or hypnotisable they are can, can explain why they respond the way they do in the rubber hand illusion. is that, is that correct?

well, the degree to which someone reports experience on a hypnosis scale predicts the degree to which they will report experience of the rubber hand illusion, given this particular context. and i'd say also, i'd point out that the scientific context perhaps has quite a lot in common with the hypnotic context. i mean the scientist wouldn't have got you in there unless they expected something to happen. if this sort of authority figure, the scientist, taking the place of the hypnotist, your expectancies are raised

what's important in this situation is the controls for demand characteristics, that is the controls for what people expect. the control for demand characteristics in rubber hand illusion studies, chiefly is this asynchronous stroking condition we discussed earlier. so the key assumption there for this to be used as a control is that people expect experience similarly for synchronous and asynchronous conditions

i think if you just introspect about that for a moment, imagine yourself receiving these two conditions. would you expect the same experience in both? i wouldn't. but, i tested it, just used a very simple procedure - this is based on ideas of Martin Orne's again from the sixties - um just basically describe the procedure to people, there was no, they didn't take part in a rubber hand illusion. showed them the video, showed the procedure, didn't say it was anything to do with illusions, or rubber hands etcetera, described the synchronous and asynchronous conditions, and showed them the synchronous and asynchronous conditions. and then just gave them the questionnaire, the standard questionnaire for the rubber hand illusion, but for what they would expect to experience, rather than what they did experience

and we find that what they expect in the synchronous condition and what they expect in the asynchronous conditions differs. that is, they expect the experience for synchronous stroking, they don't expect it for the asynchronous condition. people, on average, know that they are supposed to experience something in the synchronous condition, not the asynchronous condition

which means that there's the possibility that the rubber hand illusion, these reports and these objective measures, are compliance, bias. this is the key step we take. people responding to their ability to meet their expectancies for experience [see also the second paper]

and after twenty-two years of rubber hand experiments, and hundreds of papers reported, that message can't have, er, can't have been very welcome. how has the field taken these, these results?

it hasn't gone down well, there's complete disbelief. the thing that struck me the most is the lack of interest in the demand characteristics control issue. nobody's argued with me about that, about why that could be a valid measure for demand characteristics. erm, so i find that quite strange and surprising. but, i don't know, maybe i shouldn't be surprised and this is just how these things go, you can't expect people to open their arms to something like that

for me, i just, I focus on: we've got an alternative theory, we've got evidence consistent with that theory, and we've got evidence that the existing theory isn't as solid as was, as was thought. to me that's just normal science. if i'm wrong, then it will strengthen the rubber hand illusion, because stronger, valid controls will be developed

i don't think though, in the long term, there's nothing to lose from it. well i, i get the impression that people feel, people feel that they're losing something. i don't, i don't see it in that way, because every time we discard a particular hypothesis or find some new evidence, i mean, that's, that's science. if you go into science, you know there's going to be change, disagreement, alternative theories

in your ideal world, what would the best control look like?

the first thing is, the way that it's been done with the synchronous and asynchronous conditions, trying to show that the score is higher in the one than the other, that's fine, we can retain that. but just that they need to be matched in expectancies. you need to make sure that people expect experience in the control condition the same as they do in the illusion condition

you just had that week-long experiment and, and er, it's generated, like it's changed your life - you're now the rubber hand guy

i don't, i don't, i really didn't intend to be the rubber hand guy. and i'm gonna, i'm going to do my utmost to not be the rubber hand guy. i mean, i'm gonna, i'm doing it with other things, one after another. so i'll probably just be the guy everybody hates

are there any, any regrets you have about the whole thing?

i think i would have jumped to the end point more quickly. i think that the response, i think i thought that when i raised it in the first place, people would go: 'oh wow, that's a concern' and start thinking: 'we should have a go at sorting out these control methods'. and that isn't what happened, i had just absolute opposition, really

actually, that's mostly form the scientists. from the, from the philosophers that work in, or are peripheral to, the rubber hand illusion, who use it in their arguments, they have, there's been a lot more acceptance and even support. maybe that's because, i don't know, philosophers are more used to sort of, contentious argument in that way. that they're, kind of, that's a philosopher's job, basically, to come along and say 'i've got a different take on this, [i] disagree with you'

having more of that in science would be helpful. it would, it would, not getting so, sort of, attached maybe? not be personally invested in your data as much as possible; be aware that you're gonna be fooling yourself, and always be trying to. i mean, i'm going to be making the same mistakes, and someone will come along and, you know, if this thing manages to stand up for ten years, then someone will probably tear it apart in ten years, then i'll be angry at them. i'd like to think that i'd be able to... i'll try to, i will you know, i will certainly be trying to er, to think 'alright, well, what did you expect?'

one service we offer at the error bar is, you can confess a sin and you'll be - a science sin - and you'll be forgiven. is there anything you want to own up to?

yeah, i think that, that doing this has really kind of opened my eyes to demand characteristics. and now i'm seeing them everywhere, and it feels like, there's this situation in psychology where, to me it feels a bit like if, you know, after Fleming, and penicillin, we realised from that that you could contaminate your Petri dishes if you didn't wash them. like ten years later, twenty years later, everyone had just stopped washing their Petri dishes again. it feels a bit like, um, like it's sort of, hiding in plain sight. and now when i read papers, i think, i'm just seeing demand characteristics all over the place. and that of course applies to my own earlier work

maybe i should say that again in a way that would actually not take five minutes?

you could give it a go. just a snappy one, one-liner

otherwise you're going to be stuck there with the edit tool

um, yeah, i would say um, looking back at my own earlier work, now that i've been looking at demand characteristics, i'm starting to see them, er, in other places, i'm seeing them, you know, you become aware of this thing of will, of thinking what will the participants [be] expecting? is there any way that this could be demand characteristics? and when i look at some of my earlier studies, then, yes, there is. and, erm, i'm testing that at the moment. i hope not to be publishing a paper in a short while saying: 'yeah, my studies were demand characteristics', but, you know, we'll see