Ehrsson, HH

Fotopoulou, A

Longo, MR

Radziun, D

Tsakiris, M

English

UCL Discovery

MATTERS ARISINGNo specific relationship between hypnoticsuggestibility and the rubber hand illusionH. Henrik Ehrsson 1✉, Aikaterini Fotopoulou2, Dominika Radziun 1, Matthew R. Longo 3 &Manos Tsakiris 4,5,6✉ARISING FROM Lush et al. Nature Communications https://doi.org/10.1038/s41467-020-18591-6 (2020)In a recent study, Lush et al.1 claimed that they found substantialrelationships between hypnotizability and experimental measuresof the rubber hand illusion (RHI)2. The authors proposed thathypnotizable participants control their phenomenology to meet taskexpectations arising from the experimental paradigm. They furthersuggest that the RHI may or may not be entirely explained byhypnotic suggestions driven by task expectancies and therefore couldreflect top-down control of perception, instead of multisensorymechanisms. However, in reanalyzing their data, we observe nosignificant relationships between hypnotic suggestibility and the RHIwhen quantified using a control condition in line with standardpractice in the field and the authors’ preregistered hypothesis. Fur-thermore, we note that the relationships the authors describe areweak and observed for a visual hallucination control experience andin the control condition, indicating a general influence of hypno-tizability on cognition, rather than sensations that specifically relateto the RHI. Overall, the results from our analyses and Lush originalpaper fit well with the view that the RHI is a perceptual illusiondriven primarily by multisensory mechanisms.During the RHI, participants experience a fake hand as theirown2. In the classic version, synchronous versus asynchronousbrushstrokes are applied to the rubber hand in full view of theparticipant and to the participant’s real hand, which is hidden fromsight; the synchronous mode of stimulation elicits the illusion ofsensing touch on the rubber hand and feeling that the fake hand isone’s own. Asynchronous stroking abolishes or significantly reducesthe illusion, which is a commonly used control condition2–4.Although different theoretical models of the RHI have beenproposed5–7, there is substantial agreement that the RHI is a per-ceptual illusion that arises from a combination of bottom-up andtop-down processes involved in multisensory integration.In contrast with this view, Lush and colleagues1 concluded that theRHI arises from hypnotic suggestibility at least partially, and theyclaimed that trait phenomenological control predicts the RHI. A totalof 353 participants were tested on the RHI using the synchronous(illusion) and asynchronous (control) conditions. One-third of theparticipants were told that they would experience a stronger illusionin the synchronous conditions, another third were told that the effectwould be stronger in the asynchronous condition, and the remainingparticipants were not given instructions. According to the authors’predictions, these different suggestion instructions should influenceexpectations and the RHI, but this manipulation failed (see furtherbelow). The RHI was assessed using a standard questionnaire and a‘proprioceptive drift test’ that assessed the change in hand positionsensed toward the rubber hand. Individual differences in hypnoticsuggestibility were quantified using the Sussex-Waterloo Scale ofHypnotizability (SWASH)1. Importantly, when contrasting the syn-chronous and asynchronous conditions in the group that received nosuggestion instructions, in line with the preregistered hypothesis, noevidence for a relationship between the SWASH scale and the illusionratings was observed, and only anecdotal evidence in favor of arelationship with proprioceptive drift was shown (non-significanttwo-tailed, p= 0.074)1. We reanalyzed the entire sample to maximizethe power and observed non-significant relationships for both illu-sion ratings (Fig. 1a; p= 0.2187) and for proprioceptive drift (Fig. 1b;p= 0.3758). Moreover, a Bayesian analysis indicated that, for theillusion ratings, the null hypothesis was 5.68 times more likely thanthe alternative hypothesis (Fig. 1a); and when analyzing the illusionstatement individually we observed similar convincing evidenceagainst the preregistered hypothesis (Suppl Fig. 1A–C). Furthermore,when dividing the participants into four quartiles based on theirSWASH scores, we observed that all four groups showed significantdifferences (p < 0.001) between the synchronous and asynchronousconditions on the illusion questions (Fig. 1c). Furthermore, all fourgroups affirmed the illusion experience in the synchronous conditionin that their ratings were significantly greater than zero (p < 0.001;Fig. 1c). Thus, even the least suggestible participants showed clearevidence of experiencing the illusion.Following the unsuccessful attempt to manipulate RHI expecta-tions by explicit suggestion and inconclusive results in preregisteredhttps://doi.org/10.1038/s41467-022-28177-z OPEN1 Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden. 2 Clinical, Educational and Health Psychology Research Department, UniversityCollege London, London, UK. 3 Department of Psychological Sciences, Birkbeck, University of London, London, UK. 4 The Warburg Institute, School ofAdvanced Study, University of London, London, UK. 5 Lab of Action & Body, Department of Psychology, Royal Holloway, University of London, Egham, Surrey,UK. 6Department of Behavioural and Cognitive Sciences, Faculty of Humanities, Education and Social Sciences, University of Luxembourg, Esch-sur-Alzette, Luxembourg. ✉email: Henrik.Ehrsson@ki.se; Manos.Tsakiris@rhul.ac.ukNATURE COMMUNICATIONS |          (2022) 13:564 | https://doi.org/10.1038/s41467-022-28177-z | www.nature.com/naturecommunications 11234567890():,;analyses, Lush and colleagues used the whole sample to examine posthoc, exploratory correlations between the SWASH score and the twoillusion measures when considering the synchronous condition inisolation. However, the hypnotic suggestibility trait accounted foronly ~9% of the illusion ratings’ variability. A similar relationship wasfound for the asynchronous control condition (9%) and a controlstatement describing an ‘impossible’ experience of visual hallucina-tions (12%). Noteworthy, when subtracting the control statementratings from the illusion ratings no positive relationship withSWASH was observed (Suppl Fig. 1D–F). Thus, hypnotizabilityseems to influence cognition and experience rather broadly, but itdoes not drive the perceptions that specifically relate to the illusioncondition, i.e., the sensing of touches on the synchronously strokedfake hand and the condition-specific increase in the feeling of rubberhand ownership. Moreover, due to the nonspecificity of the post hocfindings, it cannot be excluded that they relate to different types ofcognitive biases, including behavioral compliance or response bias,rather than ‘genuine’ phenomenological control effects.The authors’ argument for leaving out the asynchronous controlcondition from the analysis was that including it is supposedly notmotivated by the literature. In support of this, they cited the 20 mostcited publications on the RHI using questionnaires or proprioceptivedrift measures, respectively, resulting in a list of 30 studies in total(Supplementary information in Lush et al.1). However, and contraryto their claims, 28 of the 30 studies used the asynchronous control toconduct critical statistical comparisons with the synchronous con-dition. Moreover, their list: (1) referred to different illusion para-digms; (2) was small in comparison to the relevant RHI studies thatoperationalized the illusion effect as differences between conditions;and (3) was not supported by recent reviews on the RHI thatFig. 1 The rubber hand illusion (RHI) is resistant to hypnotic suggestibility. a No significant relationship between trait hypnotic suggestibility (SWASH) andillusion ratings (mean of questionnaire statements S1 to S3) when comparing the synchronous (illusion) and asynchronous (control) conditions (ϱ=−0.066,p=0.219, 95% CI [−0.169, 0.039], BF01= 5.685, n= 353). b Similarly, there was no significant relationship between SWASH and proprioceptive drift whencontrasting the conditions (ϱ=0.047, p=0.376, 95% CI [−0.057, 0.151], BF01= 1.657, n= 353). cWhen dividing the participants into four quartiles based onthe trait of hypnotic suggestibility (SWASH quartiles 1–4), the illusion is significantly induced in all groups, including the least hypnotically suggestible subjects(quartile 1). The differences in illusion ratings between the synchronous and asynchronous conditions were significant in all four quartiles (1: V= 2575.5,p < 0.001, n= 88; 2: V= 2932, p < 0.001, n= 89; 3: V= 3198, p < 0.001, n= 92; 4: V= 2779.5, p < 0.001, n= 84), and the synchronous conditions werealways rated significantly >0 (1: V= 2387.5, p < 0.001; 2: V= 3258.5, p < 0.001; 3: V= 3724, p < 0.001; 4: V= 3271.5, p < 0.001). Moreover, non-parametricone-way ANOVA (Kruskal–Wallis H test) on difference in illusion ratings between the synchronous and the asynchronous conditions in four quartiles was notsignificant (χ2= 2.913, df= 3, p=0.405; a direct comparison between quartile 1 and quartile 4 in terms of condition-specific differences was also non-significant:W= 3879.5, p=0.574). d Explicit suggestions before the experiment commenced did not influence the illusion since the difference in illusion ratingbetween the synchronous and asynchronous condition was not significantly different in the three groups that were informed that they would experience thestrongest illusion in the synchronous condition (suggestion synchronous; n= 114), in the asynchronous condition (suggestion asynchronous; n= 115) or whenreceiving no information (no suggestion instruction; n= 124) (suggestion sync vs suggestion async: W= 6382, p=0.73; suggestion sync vs no suggestioninstruction: W= 7178, p=0.836; suggestion async vs no suggestion instruction: W= 7422.5, p=0.584). In all three groups, the illusion was significantlyinduced when contrasting the two conditions (V= 5438, p < 0.001; V= 4697, p < 0.001; V= 5169.5, p < 0.001). The data from Lush et al.1 are openly availableand were analyzed with RStudio software, version 1.3.1056, and the BayesFactor software package, version 0.9.12–4.2. Non-parametric tests were used(Wilcoxon signed-rank test for paired comparisons, Mann–Whitney U test for independent group comparisons) since the questionnaire data were ordinal andnot normally distributed; two-tailed tests were performed. For the Bayes factor analysis, the default Cauchy priors were used. Sync synchronous condition,Async asynchronous condition, SWASH Sussex-Waterloo Scale of Hypnotizability. The boxplots (in c and d) depict the data based on their median (thick blackline) and quartiles (upper and lower ends of boxes). The vertical lines, i.e., the whiskers, indicate the minimum or maximum values within 1.5x the interquartilerange above and below the upper and lower quartile. The circles denote outlier observations, the furthest being the minimum or maximum values in the data.MATTERS ARISING NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-022-28177-z2 NATURE COMMUNICATIONS |          (2022) 13:564 | https://doi.org/10.1038/s41467-022-28177-z | www.nature.com/naturecommunicationsemphasized the importance of using control conditions4,6. Thus, inour view, the previous literature was not reviewed correctly, and theresults of the preregistered analysis concerning condition-specificrelationships deserve more careful consideration.A critical idea in phenomenological control theory is that syn-chronous and asynchronous conditions differ in demand character-istics and implicit suggestions. Therefore, these conditions triggerdifferent phenomenological control, leading to the observed differ-ences in the RHI measures. However, this hypothesis is not sup-ported by the results, nor does it fit with the past literature. Ifdifferences in demand characteristics and implicit suggestionsbetween the two conditions lead to different degrees of phenomen-ological control, as the authors theorized, this effect should be mostpronounced in highly hypnotizable individuals. However, neither thefindings of our analysis (Fig. 1a–c) nor the preregistered analysis1support this prediction. Furthermore, if the condition-specific dif-ferences are related to demand characteristics, they should be affectedby explicit suggestions. However, we observed no significant differ-ences in RHI ratings among the three groups that received differentsuggestion instructions in our analysis (Fig. 1d). These observationsdo not support the authors’ theory but are well in line with the viewthat the RHI is a perceptual illusion, which should be resistant tosuggestions, thoughts, and high-level conceptual knowledge.A related concern is that when discussing prior literature, theauthors emphasized the effect of demand characteristics in RHIparadigms and did not address in full the past literature thatattempted to minimize and control it in various ways. For example,they did not consider previous studies that associated synchrony-asynchrony differences in the RHI to the temporal window ofmultisensory integration. Such studies systematically manipulatedthe degree of asynchrony and found that the illusion graduallydiminished as visual and tactile stimuli became increasingly tem-porally incongruent, and the RHI was abolished for asynchronies>200–300ms8–11. This precise temporal rule fits well with thetemporal window of integration of multisensory cortical neurons12,causal inference theories of multisensory integration7,11,13, and thepast body representation literature2,3,5,7–11,14,15. However, this pre-cise temporal rule is not explained by phenomenological controltheory because suggestions have been well controlled in studies usingsubtle experimental manipulations of asynchrony. Psychophysicalapproaches that better control cognitive bias have also been used inRHI studies with subtle asynchrony manipulations11.In summary, the results from the study by Lush and colleagues1provide an addition to the growing literature on individual differ-ences in the RHI. However, they do not present evidence thatfundamentally alters our understanding of the relationship betweentop-down control of experience and perceptual mechanisms.Reporting summary. Further information on research design is available in the NatureResearch Reporting Summary linked to this article.Data availabilityThe data is from Lush et al.1 and is publicly available at: https://osf.io/huwxd/. Thesource data underlying Fig. 1 and Supplementary Fig. 1 is provided as a Source Datafile. Source data are provided with this paper.Received: 16 October 2020; Accepted: 7 January 2022;References1. Lush, P. et al. Trait phenomenological control predicts experience of mirrorsynaesthesia and the rubber hand illusion. Nat. Commun. 11, 4853 (2020).2. Botvinick, M. & Cohen, J. Rubber hands ‘feel’ touch that eyes see. Nature 391, 756(1998).3. Tsakiris, M. & Haggard, P. The rubber hand illusion revisited: visuotactileintegration and self-attribution. J. Exp. Psychol. Hum. Percept. Perform. 31,80–91 (2005).4. Riemer, M. et al. The rubber hand universe: on the impact of methodologicaldifferences in the rubber hand illusion. Neurosci. Biobehav. Rev. 104, 268–280(2019).5. Tsakiris, M. My body in the brain: a neurocognitive model of body-ownership.Neuropsychologia 48, 703–712 (2010).6. Ehrsson, H. H. Multisensory Perception: From Laboratory to Clinic (eds. K.Sathian and V. S. Ramachandran) (Elsevier Inc./Academic Press, 2020).7. Samad, M., Chung, A. J. & Shams, L. Perception of body ownership is drivenby Bayesian sensory inference. PLoS ONE 10, e0117178 (2015).8. Shimada, S., Fukuda, K. & Hiraki, K. Rubber hand illusion under delayedvisual feedback. PLoS ONE 4, e6185 (2009).9. Shimada, S. et al. Relationship between sensitivity to visuotactile temporaldiscrepancy and the rubber hand illusion. Neurosci. Res. 85, 33–38 (2014).10. Costantini, M. et al. Temporal limits on rubber hand illusion reflectindividuals’ temporal resolution in multisensory perception. Cognition 157,39–48 (2016).11. Chancel, M. & Ehrsson, H. H. Which hand is mine? Discriminating bodyownership perception in a two-alternative forced-choice task. Atten. Percept.Psychophys. 82, 4058–4083 (2020).12. Avillac, M., Ben Hamed, S. & Duhamel, J. R. Multisensory integration in theventral intraparietal area of the macaque monkey. J. Neurosci. 27, 1922–1932(2007).13. Kording, K. P. et al. Causal inference in multisensory perception. PLoS ONE 2,e943 (2007).14. Longo, M. R. et al. What is embodiment? A psychometric approach. Cognition107, 978–998 (2008).15. Tsakiris, M. et al. Hands only illusion: multisensory integration elicits sense ofownership for body parts but not for non-corporeal objects. Exp. Brain Res.204, 343–352 (2010).AcknowledgementsH.H.E. was funded by European Research Council under the European Union’s horizon 2020research and innovation programme (SELF-UNITY) and the Swedish Research Council.Author contributionsH.H.E., A.F., D.R., M.R.L., and M.T. wrote the manuscript. D.R. analyzed the data andproduced the figures. All authors contributed to the revisions and approved the finalversion of the article.Competing interestsThe authors declare no competing interests.Additional informationSupplementary information The online version contains supplementary materialavailable at https://doi.org/10.1038/s41467-022-28177-z.Correspondence and requests for materials should be addressed to H. Henrik Ehrsson orManos Tsakiris.Peer review information Nature Communications thanks the anonymous reviewers fortheir contribution to the peer review of this work.Reprints and permission information is available at http://www.nature.com/reprintsPublisher’s note Springer Nature remains neutral with regard to jurisdictional claims inpublished maps and institutional affiliations.Open Access This article is licensed under a Creative CommonsAttribution 4.0 International License, which permits use, sharing,adaptation, distribution and reproduction in any medium or format, as long as you giveappropriate credit to the original author(s) and the source, provide a link to the CreativeCommons license, and indicate if changes were made. The images or other third partymaterial in this article are included in the article’s Creative Commons license, unlessindicated otherwise in a credit line to the material. If material is not included in thearticle’s Creative Commons license and your intended use is not permitted by statutoryregulation or exceeds the permitted use, you will need to obtain permission directly fromthe copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.© The Author(s) 2022NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-022-28177-z MATTERS ARISINGNATURE COMMUNICATIONS |          (2022) 13:564 | https://doi.org/10.1038/s41467-022-28177-z | www.nature.com/naturecommunications 3

No specific relationship between hypnotic suggestibility and the rubber hand illusion

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No specific relationship between hypnotic suggestibility and the rubber hand illusion

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