Dr Regine Zopf Macquarie University, Sydney, Australia

Dr Zopf is a psychologist studying how people perceive bodily sensations in eating disorders, schizophrenia & everyday life  

Dr Regine Zopf 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 hello, my name is Regine, Regine Zopf. and, er i'm currently in Sydney, Australia. and i study, i study body perception, so how we perceive our own body. and i study that in healthy participants, but also in disorders, like the eating disorders. and for that i'm particularly interested [in] how different signals of the body sort of are combined and integrated and how that influences our, our body perception, and then also how we use these signals to then interact with the world around us

would you like a drink?

yeah, sure

what can i get you? what would you like?

i might have a, erm, some red wine, maybe a Merlot?

excellent choice

it's great to have you here. our last customer was Dr Peter Lush, who's written, recently, a very controversial article about the rubber hand illusion. so can you tell me how you heard about this paper and what your thouhgts of that controversy are?

yeah, i must say that i initially found them quite interesting. i thought, 'oh there's some interesting new data', and also some interesting criticism and findings of that, are, i think interesting for the rubber hand illusion researcher

one thing i've seen on Twitter is that people have been quite upset by this controversy, or they've got quite angry about it, did those emotions not, not cross your mind?

yes, i think, i guess what crossed me more was, sort of, this strong claim based on these data, that the illusion, that the rubber hand illusion can be explained by suggestibility. i sort of can distinguish between a weak version of the data that there's something not quite right with the methods, and that response bias can influence our methods, and the sort of strong version that the whole rubber hand illusion can be explained by suggestibility, which is more the idea this implicit suggestion can control what we actually experience in the illusion. and i think it's that second sort of idea that i think has been sort of pushed quite a bit by the authors and also by the media and maybe on Twitter, and that's more what i have a problem, not a problem, but i don't agree with that. and i don't find that they actually have strong evidence for that. i'm not convinced

Peter was, very honest i think, and very um reflective about the whole process, and i think probably he maybe regrets a little bit the arguments. and i, i too found it quite strongly worded. but his argument i think is that there's this confound, that when you put people in these strange situations and you stick a rubber hand in front of them, they naturally have some expectations about what the experimenter is, is looking for he found people would systematically say: 'yeah, the synchronous stroking is going to give you a stronger illusion than the asynchronous '. how could you deal with that, do you think?

well i think there are other ways, to use measurements that are not as prone to these expectations or possible response biases that people can guess what the experimenter wants you to do, and, which might even underlie these correlations that they then found in the second study. and we always knew that, i mean it's not a new thing that we think that these subjective experiences that we sort of measure using these questionnaires could be biased by expectations and bias, and so i think um, one way is to use measures that are maybe not so prone and not so subjective. and there are quite a few as well

so his claims actually, i think they go even further than just about the, what you might call the subjective questionnaire, in fact, they're also claiming that the proprioceptive drift, and the skin conductance and maybe even other, other measures are also confounded by these expectations. do you think that's, that's a fair conclusion from his data?

like i have two parts to this, two answers, so maybe first i'll talk about why i think, why i don't really believe there's strong evidence for the suggestibility idea, although i'm, i'm intrigued by it as well and especially when you think about the rubber hand illusion, you put this hand, and then you also have the stroking and it's quite rhythmic, and i also think maybe there is something hypnotic about this. it's often dark and things like that

i don't quite, based on the data i'm not a hundred, i'm not convinced. we know there's a lot of individual differences, right? so we have often eighty percent who get the illusion and twenty percent who don't get the illusion. so, this, i think this is very intriguing, we really don't know why some people don't get the illusion. but what Lush et al found is some interesting like correlation in the synchronous condition, the measures, the subjective measures and also the drift correlates with this er suggestibility or hypnotisability

like, my second point is that these correlations can also be, be kind of explained by two types, like first it can be this response bias, or it can be explained by the implicit suggestions and then they control sort of the phenomenology to kind of respond to these expectations, so kind of the strong claim that something that happens in the rubber hand illusion by suggestion just changes the experience - doesn't have to be the case

theoretically, i think what i also have missed in this whole discussion is, i kind of think if they want to make this strong claim that what you change in the rubber hand illusion is you make these you have this implicit suggestion and it changes the phenomenology, and there's no, it has nothing to do with kind of multisensory processes or something like that, but is purely a cognitive, top-down effect, then i really believe that they also need to develop a stronger theory, and i think this theory also has to then explain some other previously-established and well-established rubber hand illusion effects

and i'm not quite sure if they can and i, and i'll give you an example, for example in the rubber hand illusion we know some factors have a strong effect and some don't. for example when i see, er, like, a hand then i can experience the rubber hand illusion, but if it's just a block of wood it's not possible to induce ownership or embodiment for that block of wood, it has to be kind of a hand, hand form is really important, that it's sort of body-like. but other factors are really not so important for the illusion, like um, especially er, the skin tone, or the details of the hands

but let's take the example skin tone. here we have basically the idea that, we know that somebody who has maybe a dark skin tone can experience the illusion for a light skin tone, and the other way around. and that's, for example, a finding that i don't really think this sort of suggestibility, er, theory can explain, because, in theory when, when i see a hand that has a different skin tone to mine i would, i would really expect that this is not my hand. but at the same time when you induce the rubber hand illusion it doesn't seem to make a difference

for me, this is something that really can't be explained by this suggestibility idea, but we, at the same time we have a lot of these multisensory theories, or multisensory theories on the rubber hand illusion that are based on multisensory processes and they often are very much based on, sort of, how we perceive something in time and space, sort of binds signals from multiple senses together, so if you feel something at the same time as we see it, this seems to be a signal that these things belong together. or if we feel, experience it in the same space, the two different signals and we are also combining them together. so these signals that are important for multisensory, er binding are really sort of important for the rubber hand illusion, whereas signals that are, maybe like skin tone is a purely visual one, we can't feel skin tone, so these don't seem to be important

so that really fits nicely with these multisensory ideas and i think a challenge is then for this other theory to really explain it

do you experience the rubber hand illusion?

yes, quite strongly, yes

because i asked Peter Lush as well, and he said no. i, i also don't really feel it any more - i used to, once upon a time. but i think i, maybe i explained it away to myself. do you think researchers are drawn into studying the rubber hand illusion in particular ways depending on how they feel the illusion?

oh, that's an interesting question, i never thought about it. maybe it, it can influence it, but i don't know, yeah maybe. i don't know, we just have an N of one and one

true, yeah

oh, there might be a study there

we need a meta-study of the, err, of rubber hand illusion researchers

so one issue that has come up in discussions with Peter and in my reading of the literature, is that, there isn't really a consensus on what, exactly is the illusion. and this is really important for the, for Lush's criticism, that do you just look at the questionnaire responses for the synchronous condition, do you look at the difference between those responses, do the responses have to be overall positive for each subject or positive for the group, or can the illusion be measured by some of these other implicit measures. so it seems that there is no real agreement between, anyone, on what the illusion is, exactly

yeah, i completely agree. it can be very messy, or has been very messy, or seems very messy. but i think one of the, sort of, reasons for this, i think that the illusion itself is so complex, that body perception is so complex. when we er have the illusion it's, sort of, it's not just that we experience ownership for the rubber hand, but we also feel embodied in this rubber hand, that the rubber hand is in that location, that the touch we feel is coming from the rubber hand being touched, and we also have a bit this feeling that we can control the rubber hand

it's very complex, and there are a lot of different aspects and it really has these multiple components, like Matthew Longo has, and his colleagues, they have um investigated a long time ago, and studied these different components like ownership, location, agency all seem to play a role in, in the rubber hand illusion and this embodiment feeling. and i think that's sort of one answer why it is so confusing what it the illusion because it really has all these aspects. um in addition to these sort of subjective measures we also have these other measures where we can observe behaviour of people in the rubber hand illusion, like how somebody reaches or how somebody responds to touches, or how somebody protects their hand or

so there are all these different aspects as well of the body protection and, and, and action and multisensory perception. um, and i think all of this is can really, is really part of the illusion and i think if one like decides on a measure it's really important that one kind of thinks about what, what the question is and what measure and what aspects one is interested in. is it like the complexity of the illusion or is it just a subset?

yeah, so i think it always depends on the question what measure's best and with each measure we should really carefully think about what potentially problems there is and how good this measure is. as long as one is clear why one does that, i think it seems OK for, like, in my opinion

do you think all these complexities can be resolved?

i think we just have to think more about the complexity, and measure, yeah measure it more more, and be, try and get the best, the best measurement we can get, and try and then tease it apart and think more about it

so overall, do you think, on current data, we can explain away the rubber hand illusion, or is there work that you think needs to be done?

yes, definitely. i don't think we can explain it away. i mean the illusion still exists in both theories, and, but i don't think we can explain away the er, like these multisensory um effects and multisensory interactions that seem to be quite important

you mentioned it before, did you see much of the discussion on social media, or, or more interestingly media reports of, of the rubber hand illusion, of this paper? and, and if you did, did that change your view of the science or did, do you just sort of ignore the media?

mmm, i think what was was really funny, i had a lot of people sending me the media reports and a lot of colleagues sending me 'oh, what do you think about this?' and 'is that the end of the rubber hand illusion?' and i thought i had to explain um, had to explain what's, what's sort of happening. so there was a lot, i felt like, it came up all the time somehow last year, and also in a lot of discussions i had, it somehow came up. and also yeah on Twitter i, i saw it. i don't really think it changed because i think i read it before, i don't think i really changed my view on it

are you able to sort of step back from all of the complexity and the arguments and the media reports, and think 'what have we learnt from Lush and colleagues' new study? and it's not just one study, it's like four or five now - they're coming out with more. yeah, what have we learnt from all of this?

yeah i think, for me, the most important thing, is that our methods, like especially the subjective measurements, can be influenced by er expectations and then response bias, and but i think that was, to me at least, clear before. i don't think that was really, er, really a new point, but it just highlights it again, and i think it's an important, something important to take away, and it should influence us, maybe we should try and maybe think about the questionnaires a bit more that we're using, and develop maybe better control questions, if that's possible, or try and, yeah, kind of discuss how we can improve what we are doing there

for the theoretical work, i think, like we discussed, i think that needs just, that needs more work for me, i'm not convinced. and at the same time, maybe it's important that people in the field who've worked on the rubber hand illusion maybe pitch different theories against each other, and maybe that's, and maybe that will be interesting to improve different theories and how we talk about them, er, and maybe yeah maybe we can improve each other's models as well

will you still be using the rubber hand illusion in your research?

yes, i will be, i think there are still some open questions, and um, i mean i don't have any direct plans at this moment, i'll, i'll be honest, but um, down the track i think if something interesting comes up, i think it's um really a great tool, because i'm interested in different signals and multisensory perception of the body, it's a great tool to introduce different conflicts in space and in time, and i think it's very very useful to get to, yeah, questions about the body, because it really allows us to manipulate something we, we were unable to manipulate before, the rubber hand illusion

so here at the error bar we can absolve you of any sins that you have made, any scientific sins. would you like to confess?

ah, yes, yeah. we talked um, we talked a bit about the complexity of the rubber hand illusion and the different questions that we can use to measure the rubber hand illusion, and i must say that early in my career, actually, because, when we analyse, we can, we can look at different components, we can look at individual questions or we could, for example, also just calculate a mean score across all the questions

erm, and one sin i, i did like is that, probably when i had my, questionnaires of my participants that i actually played around a bit and explored what might be a good way to analyse the data. and maybe tried out different options, which i don't think i would do any more like that. then later, er, became much more aware of the problem that this might create in terms of bias. and i have pre-registered a lot of my data or my analysis since, and and that's probably a sin of the past hopefully for me, that i am not really proud of, looking back

you've reformed

yeah, i just, experiencing a pre-registration process really showed me how important it is