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RESEARCH REPORT
Little evidence for an effect of the rubber hand illusion on
basic movement
Arran T. Reader
1,2
| Victoria S. Trifonova
2
| H. Henrik Ehrsson
2
1
Department of Psychology, Faculty of
Natural Sciences, University of Stirling,
Stirling, UK
2
Department of Neuroscience, Karolinska
Institutet, Stockholm, Sweden
Correspondence
Arran T. Reader, Department of
Psychology, Faculty of Natural Sciences,
University of Stirling, Stirling, UK.
Email: arran.reader@stir.ac.uk
Funding information
European Research Council; Göran
Gustafssons Stiftelse; The Swedish
Research Council
Edited by: Sophie Molholm
Abstract
Body ownership refers to the distinct sensation that our observed body belongs
to us, which is believed to stem from multisensory integration. This is com-
monly shown through the rubber hand illusion (RHI), which induces a sense
of ownership over a false limb. Whilst the RHI may interfere with object-
directed action and alter motor cortical activity, it is not yet clear whether a
sense of ownership over an artificial hand has functional consequences for
movement production per se. As such, we performed two motion-tracking
experiments (n=117) to examine the effects of the RHI on the reaction time,
acceleration, and velocity of rapid index finger abduction. We observed little
convincing evidence that the induction of the RHI altered these kinematic var-
iables. Moreover, the subjective sensations of rubber hand ownership, referral
of touch, and agency did not convincingly correlate with kinematic variables,
and nor did proprioceptive drift, suggesting that changes in body representa-
tion elicited by the RHI may not influence basic movement. Whilst experiment
1 suggested that individuals reporting a greater sensation of the real hand
disappearing performed movements with smaller acceleration and velocity
following illusion induction, we did not replicate this effect in a second experi-
ment, suggesting that these effects may be small or not particularly robust.
Overall, these results indicate that manipulating the conscious experience of
body ownership has little impact on basic motor control, at least in the RHI
with healthy participants.
KEYWORDS
body ownership, kinematics, motor control, multisensory integration
1|INTRODUCTION
When we move, we normally feel that the body we see
before us is our own. This sense of body ownership is
believed to arise through multisensory integration
(Blanke et al., 2015; Ehrsson, 2020; Ehrsson &
Chancel, 2019; Fang et al., 2019; Guterstam et al., 2018;
Kilteni et al., 2015) whereby a combination of sensory
Abbreviations: M1, primary motor cortex; PPC, posterior parietal cortex; RHI, rubber hand illusion; TMS, transcranial magnetic stimulation.
Received: 24 February 2021 Revised: 12 August 2021 Accepted: 28 August 2021
DOI: 10.1111/ejn.15444
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided
the original work is properly cited.
© 2021 The Authors. European Journal of Neuroscience published by Federation of European Neuroscience Societies and John Wiley & Sons Ltd.
Eur J Neurosci. 2021;1–24. wileyonlinelibrary.com/journal/ejn 1
cues (e.g., visual, tactile, proprioceptive, and kinaesthetic)
provides a coherent experience of an owned body that is
distinct from the world around us. However, our sense of
body ownership is surprisingly malleable. This is shown
clearly by the classic rubber hand illusion (RHI), in
which the synchronous stroking of a fake hand and the
participant’s real hidden hand can induce a sense of own-
ership over the false limb and cause the perceived posi-
tion of the real hand to drift towards the fake one
(Botvinick & Cohen, 1998). Asynchronous stroking con-
siderably weakens the illusion, and this mode of incon-
gruent visuotactile stimulation is often used as a control
condition. The RHI occurs due to the brain combining
visual information from the rubber hand with tactile and
proprioceptive information from the hidden real hand,
leading to the formation of a single coherent multisen-
sory percept of the rubber hand as one’s own
(Ehrsson, 2020; Kilteni et al., 2015; Samad et al., 2015).
When probed about the experience of their real hand
during the RHI, some individuals report that it seems like
their real hand has disappeared, that it is no longer part
of their body, or that they can no longer tell where it is
located (Lane et al., 2017; Longo et al., 2008, 2009;
Preston, 2013). However, the functional consequences of
the RHI for the ability to generate movement is unclear.
Does the illusion of owning a false hand, or ‘losing’the
real one, affect the ability to move?
Body ownership illusions seem to change the way in
which target-directed actions are performed (Burin
et al., 2019; Heed et al., 2011; Kammers et al., 2010;
Newport et al., 2010; Newport & Preston, 2011; Zopf
et al., 2011; but see Kammers, de Vignemont,
et al., 2009; Kammers, Longo, et al., 2009). However, it is
still unclear whether our ability to actually generate or
perform a movement is supported by a sense of owner-
ship over our body. Even though movement may con-
tribute to changes in the sense of body ownership
(Bassolino et al., 2018; Burin et al., 2015; Burin
et al., 2017; Dummer et al., 2009; Fiorio et al., 2011;
Kalckert & Ehrsson, 2012, 2014; Longo & Haggard, 2009;
Mangalam et al., 2019; Pyasik et al., 2019; Scandola
et al., 2017; Shibuya et al., 2018; Tidoni et al., 2014;
Tsakiris et al., 2006), how it does so is a matter of debate.
One view holds that somatosensory feedback from move-
ment contributes to body ownership (only) through mul-
tisensory integration with visual and other types of
sensory feedback (Kalckert & Ehrsson, 2012, 2014),
others that the feeling of being in voluntary control of
the movement (sense of agency, Haggard, 2017) influ-
ences body ownership (Tsakiris et al., 2006), whilst
others still have argued for a functional reciprocal rela-
tionship between body ownership and the motor system
(Burin et al., 2015; Burin et al., 2017). However, it has
not yet been established whether body ownership deter-
mines movement production. Studies using target-
directed action do not provide strong evidence for a role
of body ownership in basic movement, since actions nec-
essarily rely on accurately quantifying the spatial rela-
tionship between the body and the world. Indeed,
actions are also influenced by altering the visual–spatial
relationship between body and world, without necessar-
ily inducing changes in body ownership (e.g., Ambron
et al., 2017; Bernardi et al., 2013; Heed et al., 2011;
Holmes et al., 2006; Karok & Newport, 2010; Marino
et al., 2010).
Whilst behavioural evidence for an effect of body
ownership on low level motor control is lacking, experi-
ments using transcranial magnetic stimulation (TMS) to
record changes in corticospinal excitability and parietal-
motor cortical connectivity from muscles of the arm and
hand suggest that basic physiological markers of motor
system function are susceptible to multisensory conflict
and body illusions (Dilena et al., 2019). For example, the
illusion of missing a part of the lower arm and hand in
virtual reality has been reported to reduce corticospinal
excitability (Kilteni et al., 2016). Similarly, della Gatta
et al. (2016) observed that the RHI can result in reduced
corticospinal excitability, which they suggested is due to
disownership of the real hand. Conversely, when
using a moving version of the RHI (Kalckert &
Ehrsson, 2012), Karabanov et al. (2017) did not observe
reductions in corticospinal excitability as a result of the
illusion. They did, however, observe that ownership and
agency over a rubber hand was associated with a resting
inhibitory pattern of connectivity between the anterior
intraparietal sulcus and the primary motor cortex
(M1) (Karabanov et al., 2017). Similarly, another study
reported that the classic RHI might be associated with
inhibitory connectivity between the posterior parietal
cortex (PPC) and M1, such that those who had a greater
sensation of ownership over the rubber hand showed a
greater inhibitory PPC-M1 interaction (Isayama
et al., 2019).
The behavioural implications of these previously
reported effects of the RHI on corticospinal excitability
and parietal-motor cortical connectivity are still unclear.
Given that motor output for simple movements is
closely tied to the excitability of the motor system
(Chen et al., 1998; Davey et al., 1998; Duque
et al., 2017; Hortob
agyi et al., 2017; Leocani
et al., 2000; MacKinnon & Rothwell, 2000; Rossini
et al., 1988; Starr et al., 1988) and that the RHI might
reduce corticospinal excitability (della Gatta
et al., 2016), we might expect that such manipulations
of body ownership would have functional consequences.
Despite this, in a recent experiment, we found that
2READER ET AL.
using multisensory disintegration to reduce the subjec-
tive sense of ownership over participants’real hand—
caused by exposure to incongruent visual, tactile, and
proprioceptive information from the hand using online
digital manipulation of visual feedback—did not result
in changes in rapid finger movement (Reader &
Ehrsson, 2019). This seemed to suggest that a strong
sense of ownership over the real hand is not essential
for basic movement. However, one possibility is that
the manipulation of body ownership in the RHI has
implications for movement, whilst altering the sense of
body ownership using multisensory disintegration does
not. It is not yet clear why this should be the case, but
there are a number of potential sensory and cognitive
interactions that might feasibly play a role. For exam-
ple, changes in limb position sense from the location of
the real hand towards the rubber hand (proprioceptive
drift; e.g., Abdulkarim & Ehrsson, 2016; Botvinick &
Cohen, 1998; Tsakiris & Haggard, 2005) might create a
situation where the sensorimotor system has access to
less accurate or conflicting proprioceptive information,
leading to suboptimal planning for efferent motor com-
mands. Alternatively, an incomplete or weak RHI in
some participants could possibly create a conflict
between visual and proprioceptive representations of
the hand that is not resolved, and this conflict within
the sensorimotor system could impair its effectiveness
in controlling the hand. Finally, and admittedly specu-
latively, the fact that the rubber hand is rigid and
immobile might influence the motor system when own-
ership is experienced for such a hand that one
cannot move.
We decided to assess whether the rubber hand illu-
sion would result in changes in simple rapid finger
movement. If the manipulation of body ownership in the
RHI is sufficient to influence movement alone, then the
classic RHI should result in changes in reaction time,
peak velocity, and peak acceleration for rapid finger
movements after illusion induction. Based on the TMS
study of della Gatta et al. (2016), such illusion-induced
effects should correspond to slower reaction time,
increased peak velocity, and reduced acceleration. In our
first experiment, we also examined whether three com-
ponents of the RHI would have this effect: proprioceptive
drift, the sensation of ownership over the rubber hand,
and the sensation that the real hand has disappeared
(an experience that has been associated with feelings of
hand disownership; Longo et al., 2008, 2009). In a second
experiment, we aimed to replicate and extend the results
from the first experiment and additionally explore
possible relationships between movement generation
and sense of agency and referral of touch on the
rubber hand.
2|EXPERIMENT 1
2.1 |Methods
2.1.1 | Power analysis
We used G*Power 3.1 (Faul et al., 2007) to perform an a
priori power analysis for sample size based on an effect
size of dz =0.85. This effect size was reported by della
Gatta et al. (2016) for a difference in corticospinal excit-
ability between the synchronous and asynchronous con-
ditions of the RHI. This study appeared to be the most
directly relevant in the context of basic movement as
there is typically a link between corticospinal excitability
assessed with TMS for a given muscle (e.g., first dorsal
interosseous) and the reaction time for a movement
involving the same muscle (e.g., abduction of the right
index finger) (Chen et al., 1998; Leocani et al., 2000;
Rossini et al., 1988; Starr et al., 1988). For a two-tailed
paired ttest at 95% power, the suggested sample size was
21. Since the effect reported by della Gatta et al. was for
those susceptible to the RHI, and they suggested that dis-
ownership of the real hand might reduce corticospinal
excitability, we recruited participants until we tested at
least 21 who experienced the RHI and at least 21 who
reported a sense of disownership for their real hand, or
until we recruited 60 participants in total.
Illusion susceptibility was assessed based on level of
agreement with questionnaire statements S1.1 (owner-
ship illusion) and S1.2 (disownership illusion) described
in Section 2.1.3 (response greater than zero in the syn-
chronous condition and response greater in the synchro-
nous condition than the asynchronous condition).
Susceptibility was assessed separately for ownership and
disownership, such that participants could be categorised
as susceptible to one, neither, or both phenomena. We
did not exclude those participants who did not experience
the RHI, or did not report a sensation of disownership,
since we also planned to correlate illusion questionnaire
responses with kinematic variables, along with examin-
ing illusion-susceptible subsets.
2.1.2 | Participants
We recruited a total of 60 participants, though two were
excluded due to having less than 50% viable trials in at
least one of the conditions (see Section 2.1.5). The final
sample size used for statistical analysis was 58 partici-
pants, mean SD age =26.3 5.47 years, 29 female,
7 left-handed (self-report). Thirty-three participants were
deemed to be susceptible to the sense of ownership and
15 to disownership. Twenty-three participants did not
READER ET AL.3
report either ownership or disownership sensations as
defined by the aforementioned criteria. Participants gave
written informed consent, and the experiment was
approved by the Swedish Ethical Review Authority
(application number 2010/548-31/2 and 2018/2117).
2.1.3 | Materials and stimuli
Participants sat at a round table opposite the experi-
menter and placed their right hand behind a narrow,
L-shaped wooden screen (Figure 1a). The wooden screen
was 60 cm long in total, 54 cm high (and 18 cm long)
nearest the participant, and 31 cm high nearest the exper-
imenter. A plaster-filled life-sized male cosmetic pros-
thetic right hand (Fillauer Europe AB, Sollentuna,
Sweden) (hereby referred to as the rubber hand) was
placed left of the screen, aligned as closely as possible to
the participant’s right shoulder in order to look anatomi-
cally plausible. The middle finger of the rubber hand and
the middle finger of the real right hand were placed
20 cm apart, both 10 cm away from the screen. The par-
ticipant’s upper body and arms were covered with a black
cloth to occlude the gap between the rubber hand and
the participant’s body. The rubber arm then appeared
beneath the cloth visible to the participant in a forward-
pointing orientation so that it looked like it could be the
participant’s own limb. Tactile stimulation was applied to
the rubber hand and the participants hidden right hand
by the experimenter using two small brushes with moder-
ately soft bristles of 1 cm width (details below).
Subjective experience during the RHI was assessed
using three questionnaire items that participants were
requested to respond to on a 7-point Likert scale (3:
strongly disagree, +3: strongly agree) (Table 1). The state-
ments were adapted from previous studies (Botvinick &
Cohen, 1998; Longo et al., 2008) and aimed to assess the
sense of ownership over the rubber hand, the experience
of disownership of the real hand, and a control
statement for susceptibility and demand characteristics.
Statement S1.2 was chosen to assess a sensation of dis-
ownership of the real hand since this is in keeping with
some previous studies (della Gatta et al., 2016; Fossataro
et al., 2018) and may correlate with other statements
probing the perceptual loss of the real hand (e.g., ‘It
seemed like I could not really tell where my hand was’)
(Longo et al., 2008).
The proprioceptive drift towards the rubber hand was
assessed by placing a custom card ‘ruler’over the real
hand, centred on the middle finger, from which partici-
pants reported the number that corresponded to their felt
middle finger position. Twelve rulers were used—one for
each measurement of proprioceptive drift during the
experiment. Each was split into 21 rectangles of 1 cm
width, with a number from 1 to 21 in each rectangle. The
order of the numbers was randomised. With the central
rectangle situated over the middle finger, 10 rectangles
extended to the wooden screen (10 cm), and
10 rectangles extended laterally (10 cm). The experi-
menter placed an A4-sized cardboard screen above the
rubber hand during the recording of proprioceptive drift,
and during movements (for details, see further below).
During the movement task, the position of partici-
pants’right index finger was recorded using a wired
Polhemus Fastrak motion tracking system (Polhemus
Inc., Colchester, VT, USA) at 120 Hz with 6 degrees of
freedom (x, y, z, azimuth, elevation, and roll). The tracker
FIGURE 1 Experimental set-up and
procedure. (a) Top-down schematic of
experimental set-up (C, cloth; R, rubber
hand; M, motion-tracker; T, motion-tracking
transmitter); (b) simplified experimental
procedure
TABLE 1 Experiment 1 questionnaire statements and purpose
Item Statement Purpose
S1.1 ‘It seemed like the rubber
hand was my hand’
Feeling of ownership
over the rubber hand
S1.2 ‘It seemed like my real
hand had
disappeared’
Feeling of disownership
over the real hand
S1.3 ‘It appeared as if the
rubber hand were
drifting towards my
real hand’
Control statement
4READER ET AL.
was placed over the fingernail and attached using adhe-
sive medical tape. Data were collected in MATLAB
R2017b (MathWorks, Inc., Natick, MA, USA) for offline
analysis using a custom script and functions from
the HandLabToolBox (https://github.com/TheHandLab/
HandLabToolBox). Participants wore headphones
(Maxell, Tokyo, Japan) to provide them with audio trig-
gers indicating when to move their index finger (see
details in Section 2.1.4).
2.1.4 | Procedure
Participants took part in two blocks (synchronous and
asynchronous tactile stimulation conditions), which were
counterbalanced (Figure 1b). Each block consisted of
10 movement trials, each consisting of a 30-s period
of repeated visuotactile stimulation delivered to the rub-
ber hand and the hidden real hand followed by a finger
movement, and three measurements of proprioceptive
drift (which also included a 30-s period of repeated
visuotactile stimulation). Proprioceptive drift was regis-
tered in trials (without movement) at the start and end of
each block, as well as following the fifth trial (see below
for details). The procedure was designed to maximise the
number of movement trials that could be collected and
minimise participant boredom (e.g., by breaking up
movement trials with proprioceptive drift). We wanted to
ensure that participants would remain focussed and alert
throughout the experiment and ready to rapidly respond
when needed. During the experiment, participants were
instructed to place their right hand palm down on the
table in a posture matched with the rubber hand (digits
relaxed, slightly apart). They were asked to relax their
right hand and arm during all periods of visuotactile
stimulation and proprioceptive drift measurement as
movement can disrupt the RHI and the drift. The experi-
menter was visible to the participant throughout the
entire experiment.
During the movement task, participants observed the
rubber hand whilst tactile stimulation was applied (prior
to performing the movement). At the start of each trial,
the experimenter pressed a key on a keyboard placed on
their lap, which triggered a timer on the computer used
for motion-tracking. The experimenter also initiated an
audio file on a smartphone which, after 2 s, began
playing a tone through the headphones worn by the
experimenter. This tone was used by the experimenter to
time the tactile stimulation, which was applied
to the middle finger of the rubber hand, from
the metacarpophalangeal to the distal interphalangeal
joint, at a frequency of 0.5 Hz (1 s on, 1 s off), for 30 s.
This relatively short duration was used to allow more
movement trials and is sufficient for illusion induction,
which has previously been found to occur within less
than 20 s (Chancel & Ehrsson, 2020; Ehrsson et al., 2004;
Lloyd, 2007). In the synchronous condition, stimulation
was also applied to the participant’s own middle finger,
matched as closely as possible to that performed on the
rubber hand. In the asynchronous condition, stimulation
of the participant’s hand was applied in a medial to lat-
eral direction over the top of the hand (just below the
metacarpophalangeal joints), during the ‘off’period of
the rubber hand stimulation. Thus, the asynchronous
condition included both temporal and spatial incongru-
ence of the visual and tactile information from the hand,
a combination that is known to strongly suppress the sen-
sation of body ownership (e.g., Gentile et al., 2013).
For movement trials in both conditions, following tac-
tile stimulation, the experimenter obscured the view of
the rubber hand by holding the cardboard screen approx-
imately 1 cm above it, and pressed a key on the keyboard.
This stopped the timer (providing a record of trial dura-
tion, for preprocessing below) and triggered a random-
ised interval of 0.2–2 s, after which a tone played in the
headphones provided to the participant. This signalled
them to, as quickly as possible, abduct their index finger
from a resting position to maximal abduction (moving
the index fingertip approximately 4–6 cm to the left).
They maintained the abduction until a second, lower pit-
ched tone played 1 s later, signalling them to relax their
finger again. Participants were then requested to observe
their real hand and move their fingers to remove any illu-
sory sense of ownership over the rubber hand and thus to
avoid carry-over effects for the next trial. When the rub-
ber hand was obscured prior to movement, participants
were required to look at and keep their attention
focussed towards the location of the rubber hand (behind
the cardboard screen), and not to change the direction of
their gaze (i.e., to avoid switching their attention). The
experimenter checked that the participants complied
with this instruction and they were reminded of this if
necessary.
The rubber hand illusion is associated with a proprio-
ceptive drift in the direction of the rubber hand
(Abdulkarim & Ehrsson, 2016; Botvinick & Cohen, 1998;
Tsakiris & Haggard, 2005). Proprioceptive drift is attained
by subtracting the participant’s felt position of their real
hand after illusion induction from the perceived position
of their real hand before illusion induction. For obtaining
the initial pre-induction proprioceptive drift measure-
ment, the experimenter always reset the participant’s pro-
prioceptive estimate of their right hand by lifting and
moving it away from the wooden screen, in a lateral
direction, then replacing it at the original position on
the table 20 cm away from the rubber hand. The
READER ET AL.5
experimenter obscured the rubber hand (with the card-
board screen, see above), placed the ruler above the par-
ticipant’s real hand, and then asked the participant to
verbally state the number under which they felt the tip of
their middle finger on their hidden right hand. Tactile
stimulation was then performed for 30 s as described
above, the rubber hand obscured again, and a new pro-
prioceptive drift measurement (post-induction) of middle
finger position recorded using a new randomised selec-
tion of numbers. The experimenter then moved the par-
ticipant’s right hand laterally once again to re-establish
veridical proprioception and asked them to observe and
move their fingers in order to fully eliminate any
remaining RHI and avoid carry-over effects, before the
right hand was placed back in the required position for
the next trial.
Following both blocks, two more 30-s periods of
visuotactile stimulation were applied, one for
each condition (synchronous, asynchronous), in the
counterbalanced order used for that participant. After
tactile stimulation was applied, the experimenter
obscured the rubber hand and verbally presented the par-
ticipants with the three questionnaire statements
(as described above) in a random order, storing their sub-
sequent verbal responses on a computer for offline analy-
sis. The participant was again asked to observe their real
hand and move their fingers between the two periods of
tactile stimulation in order to eliminate carry-over
effects.
2.1.5 | Data analysis
A custom automated script written in Python 3 was used
for extracting questionnaire and proprioceptive drift
responses, as well as pre-processing and extraction of
kinematic variables from motion-tracking position data.
The first 10 samples of every movement trial (83 ms)
were removed from position data due to a brief but con-
sistent artefact occurring at the onset of sampling.
Eighty-three milliseconds were subsequently added to
reaction time for each trial to account for this. Single
timepoint spikes (>3 SD from the mean) in each trial’s
double-differentiated time series were deemed electro-
magnetic artefacts and removed by replacing the value
with the mean of two adjacent samples on either side;
4.60% of samples were interpolated in this fashion. Posi-
tion data were then filtered with a second-order dual-pass
Butterworth filter, with a 10-Hz low-pass cut-off.
Reaction time was classed as the time between the
tone indicating the participant to move and the
tracker 3D velocity reaching an arbitrary value of
2.5 cm/s. Movement end time was considered the point
at which the tracker 3D velocity returned below 2.5 cm/s,
and the 3D peak velocity was extracted from between the
reaction time and this timepoint. Three-dimensional
peak acceleration was extracted from between the reac-
tion time and the time of peak velocity.
Trials in which the reaction time was shorter than
200 ms (suggesting a false start) or longer than 800 ms
(suggesting a delayed start), or in which the peak velocity
was smaller than 5 cm/s (suggesting non-rapid action) or
greater than 100 cm/s (suggesting a remaining artefact),
were excluded. Trials were also excluded if the time from
reaction time to peak velocity was unusually short
(<33 ms) or long (>200 ms). Since we were interested in
the first, rapid digit abduction, trials were not excluded if
the participant returned their finger prior to the tone
indicating them to do this. However, trials were excluded
if peak velocity was preceded by a local reduction in
velocity (i.e., if participants slowed or stopped during
their initial movement, or they returned their finger too
early but more rapidly than their initial abduction). Trials
were also excluded if tactile stimulation was not applied
for the full 30 seconds before the tone to signal move-
ment was triggered. The 3D velocity profiles for every
trial were visually inspected for remaining artefacts. Par-
ticipants with less than five trials in either block were
excluded entirely (only 2 out of 60 participants). For the
remaining participants, 90.5% of trials were maintained
for statistical analysis. For every participant, mean values
for each kinematic variable over each trial were calcu-
lated for each condition (synchronous, asynchronous).
All statistical analyses were performed in JASP (JASP
Team, 2019). Questionnaire items were compared across
conditions using Wilcoxon signed-rank tests, with the
effect size rgiven as the rank-biserial correlation.
The mean proprioceptive drift value for each participant
for each condition was calculated by taking the mean
value for each proprioceptive drift assessment (post-
induction–pre-induction). Since a Shapiro–Wilk test indi-
cated a deviation from normality, proprioceptive drift
across conditions was also compared using a Wilcoxon
signed-rank test. We planned to exclude any participants
who provided a rating >0 to all questionnaire statements
(including the control statement) in every condition,
which would suggest high susceptibility to agreement,
though none met this criterion.
Kinematic variables were checked for normality using
a Shapiro–Wilk test and then compared across conditions
using two-tailed paired ttests. Hedges’g
rm
was used to
assess effect sizes (Lakens, 2013). We also performed
Bayesian paired samples ttests (Rouder et al., 2009) in
JASP, using a default Cauchy prior with a scale of 0.707,
zero-centred (where 50% of the density is located between
effect sizes 0.707 and 0.707, for a two-sided hypothesis).
6READER ET AL.
This prior distribution effectively specifies an alternative
hypothesis in which one is 50% confident that the true
effect size lies between 0.707 and 0.707. This analysis
provided information regarding the level of support for
the null hypothesis (synchronous =asynchronous)
compared with the alternative hypothesis, or for the
alternative hypothesis (synchronous ≠asynchronous)
compared with the null hypothesis, given the data. We
used a typical heuristic for assessing evidence for either
hypothesis, in which BF
10
> 3 suggests better support for
the alternative hypothesis, and BF
10
< 0.333 better sup-
port for the null hypothesis (Jarosz & Wiley, 2014;
Raftery, 1995). The hypothesis was that, should the RHI
have a general effect on rapid movement, then in the syn-
chronous condition reaction time should be greater and
peak acceleration and peak velocity should be smaller.
To assess whether those who reported a greater sense
of ownership over the rubber hand in the synchronous
condition also had a greater reaction time and smaller
peak velocity and peak acceleration, we correlated
change in response to S1.1 across conditions with the
change in kinematic variables. This was done with
Kendall rank correlations (tau-b), along with Bayesian
Kendall rank correlations (stretched beta prior width of
1, i.e., a non-informative prior) (van Doorn et al., 2018).
To assess whether those who showed a greater sense of
disownership for their real hand had a greater reaction
time, and smaller peak velocity and peak acceleration,
we performed an identical analysis for S1.2. To assess
whether those who showed a stronger proprioceptive
drift of their hand position sense towards the rubber
hand had a greater reaction time, and smaller peak veloc-
ity and peak acceleration, we also performed this analysis
for proprioceptive drift.
Finally, we compared kinematic variables (reaction
time, peak acceleration, and peak velocity) between con-
ditions on different illusion-susceptible subsets of individ-
uals using a Bayesian approach, in order to ascertain how
convincing any correlation (or absence of correlation)
was under different prior distributions. Illusion-
susceptible subsets were defined as those who had both a
greater value for the illusion component (questionnaire
items or proprioceptive drift) in the synchronous versus
asynchronous condition and a value greater than zero in
the synchronous condition. We used one-sided Bayesian
ttests with the default Cauchy prior, as well as two nor-
mally distributed priors centred on two different effect
sizes. The first effect size was based on dz =0.85 reported
by della Gatta et al. (2016). We reasoned that since exter-
nally induced motor-evoked potentials (i.e., through a
magnetic pulse applied over M1) could result in a larger
effect than might be observed in naturalistic movement,
our second prior was centred on half this effect size
(0.43). The SD of the prior distributions was set at 0.22,
such that the medians of the two alternate distributions
were separated by approximately 2 SDs. For reaction time
we assessed the alternative hypothesis that synchro-
nous > asynchronous, whilst for peak acceleration and
peak velocity we assessed the alternative hypothesis that
asynchronous > synchronous. We also performed two-
tailed paired ttests for reference.
In all Bayesian analyses, we also assessed the robust-
ness of the Bayes factor. That is, we report the maximum
possible Bayes factor and the associated scaling value of
the default prior distribution (i.e., the Cauchy prior width
or stretched beta prior width) (van Doorn et al., 2021).
2.2 |Results
2.2.1 | Questionnaire
There was a statistically significant difference between
the level of agreement to statement S1.1 across the syn-
chronous and asynchronous conditions (W=1156,
p< 0.001, r=0.351), confirming that participants
reported a greater sense of ownership over the rubber
hand in the synchronous condition as expected
(Figure 2). In addition, participants were less certain in
rejecting the feeling that the real hand had
disappeared—a marker of hand disownership—in the
synchronous condition, as reflected in a statistically sig-
nificant difference between the conditions in responses to
S1.2 (W=483, p< 0.001, r=0.436). There was a
statistically significant difference between the conditions
in responses to control statement S1.3 (W =255,
p=0.0110, r=0.702), though a post hoc assessment of
the magnitude of this difference (synchronous–
asynchronous) indicated that it was less than was
observed between the conditions in S1.1 (W=1122,
p< 0.001, r=0.311) and S1.2 (W=472, p=0.0265,
r=0.448).
2.2.2 | Proprioceptive drift
There was a statistically significant difference in the
extent of proprioceptive drift towards the rubber hand
between the synchronous and asynchronous conditions
(W=765, p=0.0139, r=0.106), suggesting that pro-
prioceptive drift towards the false hand was greater in
the synchronous (mean SE =0.305 0.0682 cm) com-
pared with the asynchronous (0.0402 0.0774 cm) con-
dition (Figure 2). Since the proprioceptive drift in the
synchronous condition appeared to be relatively small
compared with that observed in some previous studies
READER ET AL.7
(e.g., (Abdulkarim & Ehrsson, 2016; Tsakiris et al., 2008;
Tsakiris & Haggard, 2005), we decided post hoc to also
perform a one-tailed Wilcoxon signed-rank test which
confirmed that proprioceptive drift in this condition was
greater than zero (V=827, p< 0.001, r=0.0333).
2.2.3 | Kinematics
There was no statistically significant difference for reaction
time (Figure 3) between the synchronous (496 8.07 ms)
and asynchronous (502 8.27 ms) conditions (t(57)
=1.02, p=0.312, g
rm
=0.100, BF
10
=0.235, max
BF
10
=1.00 at Cauchy prior width 0.0005). There was also
no statistically significant difference for peak acceleration
between the synchronous (351 19.2 cm/s
2
) and asyn-
chronous (359 22.9 cm/s
2
)conditions(t(57) =0.625,
p=0.534, g
rm
=0.0423, BF
10
=0.172, max BF
10
=1.00 at
Cauchy prior width 0.0005). There was no statistically
significant difference for peak velocity between
the synchronous (19.4 0.879 cm/s) and asynchronous
(19.8 1.04 cm/s) conditions (t(57) =0.672, p=0.504,
g
rm
=0.0505, BF
10
=0.178, max BF
10
=1.00 at Cauchy
prior width 0.0005). The Bayes factor suggested greater
support for the null than the alternative hypothesis in all
cases. The robustness checks suggested that even exceed-
ingly narrow priors with the majority of the density sur-
rounding zero did not provide support for the alternative
hypothesis. Example velocity plots are provided in
Figures S1 and S2.
2.2.4 | Correlation
We observed statistically significant negative correlations
between change in perceived hand disownership (S1.2)
FIGURE 2 Experiment 1 questionnaire and proprioceptive drift results. Coloured circles indicate individual participant values
8READER ET AL.
across the synchronous and the asynchronous conditions
and change in peak acceleration (r
τ
=0.285,
p=0.00420) and peak velocity (r
τ
=0.270,
p=0.00681, Table 2) between the same conditions. The
Bayes factor suggested greater support for the alternative
hypothesis than the null in both cases. This result
suggested that the more that individuals tended to feel
like their real hand had disappeared in the synchronous
compared to asynchronous condition, the smaller their
movement acceleration and velocity in the synchronous
condition (Figure 4). To confirm that this result was not
driven by participant suggestibility in the illusion, we
decided post hoc to re-run these correlations after remov-
ing any individuals who reported a higher rating for con-
trol statement S1.3 in the synchronous condition than in
FIGURE 3 Experiment 1 kinematic results. Coloured circles
indicate individual participant values
TABLE 2 Experiment 1 change in illusion measures correlated with change in kinematic variables (synchronous–asynchronous)
Reaction time Peak acceleration Peak velocity
r
τ
pBF
10
Bayes factor
robustness
r
τ
pBF
10
Bayes factor
robustness
r
τ
pBF
10
Bayes factor
robustness
Max
BF
10
Stretched
beta prior
width
Max
BF
10
Stretched
beta prior
width
Max
BF
10
Stretched
beta prior
width
S1.1 0.107 0.262 0.341 1.03 0.0164 0.162 0.0905 0.827 1.70 0.0827 0.196 0.0407 1.71 2.96 0.146
S1.2 0.00852 0.932 0.171 1.00 0.0001 0.285 0.00420 23.2 29.4 0.324 0.270 0.00681 13.7 18.2 0.290
Proprioceptive drift 0.118 0.208 0.394 1.09 0.0256 0.0723 0.441 0.234 1.00 0.0001 0.125 0.181 0.441 1.15 0.0369
READER ET AL.9
the asynchronous condition. The results held for both
peak acceleration (r
τ
=0.472, p< 0.001, BF
10
=1201)
and peak velocity (r
τ
=0.397, p=0.00134,
BF
10
=96.1).
We also observed a statistically significant negative
correlation between change in rubber hand ownership
(S1.1) for synchronous versus asynchronous and change
in peak velocity for the same contrast (p=0.0407,
Table 2), possibly suggesting that the more that individ-
uals felt like the rubber hand was their hand in the syn-
chronous compared to asynchronous condition, the
smaller their peak velocity in the synchronous condition.
However, the Bayes factor, in this case, did not provide
conclusive support for either the null or the alternative
hypothesis, suggesting that this result be interpreted with
caution. The same was true for most other correlations
performed (Table 2), including the correlations between
proprioceptive drift and reaction time/peak velocity.
2.2.5 | Assessment of illusion-susceptible
subsets
Ownership
For those susceptible to the feeling of ownership over the
rubber hand (S1.1, n=33), 52% of the subset showed an
increased reaction time in the synchronous condition
compared with the asynchronous condition (493 10.8
versus 497 10.9 ms, t(32) =0.400, p=0.692,
g
rm
=0.0500), whilst 58% showed a reduced peak
acceleration (348 27.9 versus 359 32.7 cm/s
2
,t(32)
=0.822, p=0.417, g
rm
=0.0532), and 48%
showed a reduced peak velocity (19.3 1.27 versus
19.9 1.49 cm/s, t(32) =0.960, p=0.344,
g
rm
=0.0721). The normally distributed prior centred on
0.85 suggested greater support for the null hypothesis for
reaction time (BF
10
=0.00306), peak acceleration
(BF
10
=0.0373), and peak velocity (BF
10
=0.0524). The
normally distributed prior centred on 0.43 suggested
greater support for the null hypothesis for reaction time
(BF
10
=0.115), though we could not draw strong conclu-
sions regarding either hypothesis for peak acceleration
(BF
10
=0.518) and peak velocity (BF
10
=0.642). Ana-
lyses using the default Cauchy prior (width 0.707, zero-
centred) suggested greater support for the null hypothesis
for reaction time (BF
10
=0.141, max BF
10
=0.993 at
Cauchy prior width 0.0005), but again we could not draw
strong conclusions for either hypothesis for peak acceler-
ation (BF
10
=0.399, max BF
10
=1.10 at Cauchy prior
width 0.0343) and peak velocity (BF
10
=0.466, max
BF
10
=1.16 at Cauchy prior width 0.0606).
These results suggested that even in individuals sus-
ceptible to the rubber hand illusion, an explicit sensation
of ownership over the rubber hand was unlikely to inter-
fere with reaction time, and unlikely to induce large
changes in peak acceleration or peak velocity. However,
we were not able to rule out the possibility of smaller
effects on peak acceleration and peak velocity.
Disownership
For those susceptible to the feeling of the real hand dis-
appearing (S1.2, n=15), 46% of the subset showed an
increased reaction time in the synchronous condition
compared with the asynchronous condition (502 18.3
versus 511 19.6 ms, t(14) =0.682, p=0.506,
g
rm
=0.116), whilst 73% showed a reduced peak accelera-
tion (301 37.9 versus 330 45.9 cm/s
2
,t(14) =1.78,
p=0.0961, g
rm
=0.145), and 67% showed a reduced
peak velocity (16.9 1.66 versus 18.5 1.98 cm/s, t(14)
=2.06, p=0.0586, g
rm
=0.211).
The normally distributed prior centred on 0.85
suggested greater support for the null hypothesis for
reaction time (BF
10
=0.0101), and we could not draw
strong conclusions for either hypothesis when assessing
peak acceleration (BF
10
=1.89). However, there was
evidence in favour of the alternative hypothesis
(asynchronous > synchronous) for peak velocity
(BF
10
=3.62). The normally distributed prior centred on
0.43 suggested greater support for the null hypothesis for
reaction time (BF
10
=0.171), but the Bayes factor
suggested greater support for the alternative hypothesis
for both peak acceleration (BF
10
=3.48) and peak
FIGURE 4 Scatterplot of change in disownership statement
S1.2 (‘It seemed like my real hand had disappeared’) versus change
in peak velocity (synchronous–asynchronous). Coloured circles
indicate individual participant values
10 READER ET AL.
velocity (BF
10
=5.17), consistent with the correlation
reported above. Analyses using the default Cauchy prior
suggested greater support for the null hypothesis for reac-
tion time (BF
10
=0.171, max BF
10
=0.994 at Cauchy
prior width 0.0005), but we could not draw strong
conclusions for either hypothesis for peak acceleration
(BF
10
=1.77, max BF
10
=2.19 at Cauchy prior
width 0.286) and peak velocity (BF
10
=2.62, max
BF
10
=2.99 at Cauchy prior width 0.331).
These results generally supported the correlation
between S1.2 and peak acceleration and peak velocity,
suggesting that the experience of the real hand dis-
appearing in the synchronous condition might have
weakly interfered with the acceleration and velocity, but
not the reaction time, of rapid finger movements. This
indicated that the relationship with the feeling of disap-
pearance extended to the performance, rather than the
initiation, of movement.
Given the small size of the S1.2 subset, we decided
post hoc to examine whether these were individuals who
also had a greater feeling of ownership over the rubber
hand or proprioceptive drift. Comparing this subset with
the rest of the sample using a Mann–Whitney Utest
suggested that they had a greater level of agreement to
statement S1.1 in the synchronous condition (median
response =2 versus 1, W=519, p< 0.001), but there
was no statistically significant difference between the
groups in proprioceptive drift (median drift =0.333 cm
in both groups, W=351, p=0.618). This suggested that
the S1.2 subset consisted of individuals who felt a greater
degree of ownership over the rubber hand during the
illusion.
Proprioceptive drift
For the subset susceptible to proprioceptive drift (n=26)
62% showed an increased reaction time in the synchro-
nous condition compared with the asynchronous condi-
tion (505 13.8 versus 502 13.7 ms, t(25) =0.352,
p=0.728, g
rm
=0.0423), whilst 50% showed a reduced
peak acceleration (357 26.7 versus 369 33.1 cm/s
2
,
t(25) =0.604, p=0.551, g
rm
=0.0689), and 50%
showed a reduced peak velocity (19.0 1.25 versus
19.9 1.51 cm/s, t(25) =0.913, p=0.370,
g
rm
=0.111).
The normally distributed prior centred on 0.85
suggested greater support for the null hypothesis for reac-
tion time (BF
10
=0.0214), peak acceleration
(BF
10
=0.0376), and peak velocity (BF
10
=0.0786). The
normally distributed prior centred on 0.43 suggested
greater support for the null hypothesis for reaction time
(BF
10
=0.325), though we could not draw strong conclu-
sions for either hypothesis for peak acceleration
(BF
10
=0.455) and peak velocity (BF
10
=0.712).
Analyses using the default Cauchy prior suggested
greater support for the null hypothesis for reaction time
(BF
10
=0.277, max BF
10
=1.00 at Cauchy prior width
0.00430), but we could not draw strong conclusions for
either hypothesis for peak acceleration (BF
10
=0.351,
max BF
10
=1.03 at Cauchy prior width 0.0230) and peak
velocity (BF
10
=0.487, max BF
10
=1.14 at Cauchy prior
width 0.0569).
These results suggested that proprioceptive drift
towards the rubber hand was unlikely to interfere with
reaction time, and unlikely to induce large changes in
peak acceleration or peak velocity. However, we were not
able to rule out the possibility of smaller effects on peak
acceleration and peak velocity.
2.2.6 | Post hoc exploratory regression
Since Bayesian analyses did not always provide reason-
able support for either the null or alternative hypotheses
when correlating illusion measures with kinematics and
examining small effects in illusion-susceptible subsets,
we decided to perform exploratory multiple regression.
The purpose of this analysis was to assess if changes in
peak acceleration and peak velocity were predicted by
change in illusion measures. In all analyses we
checked the linearity of the relationship between the
dependent variable and independent variables, and
assessed multicollinearity between independent variables
(jrj< 0.500 in all cases). Independence (1 < Durbin-
Watson < 3), homoscedasticity, and normal distribution
of residuals were also checked. Standardised residuals
greater than 3 were removed (never more than one par-
ticipant in any analysis).
First, a multiple regression was performed to predict
the difference in peak acceleration between conditions
from the difference in S1.1, S1.2, and proprioceptive drift
(forced entry method). The model appeared to provide a
prediction for change in peak acceleration (F(3, 56)
=3.22, p=0.0299, adj. R
2
=0.106). Change in S1.1 or
proprioceptive drift was not related to change in peak
acceleration, but change in S1.2 negatively predicted
change in peak acceleration (Table 3), in keeping with
the aforementioned correlation. Removing S1.1 and pro-
prioceptive drift from the model did not drastically
change the predicted variance (F(1, 56) =7.53,
p=0.00818, adj. R
2
=0.104, β=0.347).
A second multiple regression was performed to pre-
dict the change in peak velocity between conditions
based on change in S1.1, S1.2, and proprioceptive drift.
This resulted in a model that provided a prediction for
change in peak velocity (F(3, 57) =4.20, p=0.00964,
adj. R
2
=0.144). Change in S1.2 or S1.1 were not related
READER ET AL.11
to change in peak velocity, but change in proprioceptive
drift negatively predicted change in peak velocity
(Table 3). Removing S1.1 and S1.2 reduced the variance
predicted by over half (F(1, 57) =3.75, p=0.0579, adj.
R
2
=0.0460, β=0.250). Removing S1.1 and
proprioceptive drift slightly reduced the predicted
variance (F(1, 56) =6.61, p=0.0130, adj. R
2
=0.0910,
β=0.327). These results suggested that change in S1.2
could possibly predict 10% of the variance in the change
in peak acceleration and peak velocity, following illusion
induction.
2.3 |Discussion
We tested whether the RHI influences basic movement.
We observed that reaction time and finger movement
acceleration and velocity were virtually unaffected by the
RHI when we compared the synchronous and asynchro-
nous conditions (with Bayesian analyses indicating sup-
port in favour of the null hypothesis), suggesting that
simply manipulating visuotactile and visuoproprioceptive
information to interfere with body ownership may not
influence motor performance (see also Reader &
Ehrsson, 2019).
We also assessed the effects of different components
of the illusion (sense of ownership over the rubber
hand, feeling of real hand disownership, and proprio-
ceptive drift) on movement. We did not observe con-
vincing evidence for effects of proprioceptive drift on
rapid finger movements, and an exploratory regression
analysis suggested that change in proprioceptive drift
predicted little change in kinematics. A feeling of own-
ership over the rubber hand did not show any reliable
systematic relationship with any of the movement
parameters, but we could not draw strong conclusions
regarding a possible negative correlation between S1.1
ratings and peak velocity (r
τ
=0.196, p=0.0407,
BF
10
=1.71). However, that clear effects of ownership
over the rubber hand were not observed in the illusion-
susceptible subset suggests treating this correlation with
caution.
Our most notable finding was that those who felt
more like their real hand had disappeared in the syn-
chronous relative to asynchronous condition, or at least
displayed uncertainty in denying this statement, also
performed finger movements with a slower acceleration
and velocity. The absence of similar effects on reaction
time suggests that this relationship was specific to
motor performance, rather than initiation. The effect
was confirmed when examining only the individuals
susceptible to the feeling of disappearance. Overall this
result seemed to suggest that a feeling of the real hand
disappearing during the RHI, which may reflect experi-
ences related to real hand disownership more generally,
might interfere with basic movement. However, an
exploratory regression suggested that an increased sen-
sation of the real hand disappearing might explain only
10% of the variance in the change in acceleration and
velocity. This may have been due to the fact that few
participants explicitly reported a feeling of their real
hand disappearing (only 15/58 participants gave an
affirmative rating ≥1), or that this statement is
ineffective at capturing different individuals’feelings of
real hand disownership during the RHI. It is
also possible that some reports of disappearance
are only post-perceptual reflections or judgements
(de Vignemont, 2011) that arise in a subgroup of indi-
viduals when they consider (at a cognitive level) what
is going on (i.e., ‘I really feel like the rubber hand is
my hand, so what has happened to my real hand
behind the screen?’).
With the above in mind, we decided to perform a sec-
ond experiment with a greater number of statements
addressing the feeling of real hand disownership, in the
hope that this would allow us to better capture different
participant experiences and therefore any effects on
movement. We also decided to add statements to capture
other conscious experiences that might feasibly interfere
with movement. For example, if changes in corticospinal
excitability during the RHI result from an altered influ-
ence of somatosensory and parietal inputs to the motor
cortex (Isayama et al., 2019), then the referral of touch
from the real to the false hand might feasibly be related
TABLE 3 Experiment 1 initial exploratory multiple regression outputs
Variable
Peak acceleration Peak velocity
βtpβtp
Intercept 1.75 0.0854 1.82 0.0737
S1.1 0.109 0.766 0.447 0.149 1.08 0.283
S1.2 0.319 2.25 0.0286 0.267 1.95 0.0566
Proprioceptive drift 0.168 1.31 0.196 0.306 2.46 0.0172
12 READER ET AL.
to changes in movement. In addition, changes in the
capacity to execute rapid finger movement could also
result from a feeling of ownership over a rigid artificial
hand that one cannot move, which speculatively could
lead to a reduction in agency, or an incomplete multisen-
sory percept of the hand (i.e., to some degree one some-
how feels like they have more than one right hand
during the illusion).
3|EXPERIMENT 2
3.1 |Methods
Unless otherwise stated, all methods were identical to
Experiment 1.
3.1.1 | Participants
We aimed to test at least 60 participants, in keeping with
Experiment 1. We recruited 69 participants, though five
were excluded due to an inadequate number of valid tri-
als, and five were excluded due to technical difficulties
during data collection. The final sample size used
for statistical analysis was 59 participants, mean SD
age =26.4 5.63 years, 30 female, 6 left-handed (self-
report). Participants gave written informed consent, and
the experiment was approved by the Swedish Ethical
Review Authority (application number 2010/548-31/2
and 2018/2117).
3.1.2 | Materials and stimuli
Questionnaire items were adapted from previous studies
(Longo et al., 2008; Newport & Preston, 2011;
Preston, 2013), aside from the control statement. The
statements aimed to assess the sense of ownership over
the rubber hand, referral of touch, the potential for
agency over the rubber hand, the perceptual experience
of having more than one hand, a sense of disownership
for the real hand, and a control statement for compliance
and susceptibility (Table 4).
3.1.3 | Procedure
The experimental protocol was identical to
Experiment 1, except that no measurement of
proprioceptive drift was recorded, 12 movements were
recorded per condition, and an extended questionnaire
(Table 4) was used.
3.1.4 | Data analysis
Questionnaire items were compared across conditions
using Wilcoxon signed-rank tests, with the effect size r
given as the rank-biserial correlation. An FDR-corrected
alpha value was used for assessing statistical significance
(Benjamini & Yekutieli, 2001).
A total of 4.54% of samples were interpolated in place
of electromagnetic artefacts; 84.6% of movements were
maintained following pre-processing. We decided to focus
our analysis on reaction time and peak velocity, since
peak velocity and peak acceleration were very strongly
TABLE 4 Experiment 2 questionnaire statements and purpose
Item
Statement
(‘It seemed like …) Purpose
S2.1 …the rubber hand was
my hand’
Feeling of ownership
over the rubber hand
S2.2 …the touch I felt was
caused by the brush
touching the rubber
hand’
Referral of touch
S2.3 …I could have moved the
rubber hand if I had
wanted’
Potential for agency over
the rubber hand
S2.4 …I had two right hands’Experience of having
more than one hand
a
S2.5 …my real hand had
disappeared’
Feeling of disownership
over the real hand
S2.6 …I could not really tell
where my real hand
was’
S2.7 …I was unable to move
my real hand’
S2.8 …my real hand no longer
belonged to me’
S2.9 …my real hand was no
longer part of my
body’
S2.10 …the rubber hand
replaced my real
hand’
b
S2.11 …the rubber hand was
changing colour’
Control statement
a
Note that although this statement typically is used as a control statement in
RHI studies, we were here interested in exploring the possibility that weaker
rejection of this statement could be related to changes in kinematics,
perhaps due to a more incoherent visuoproprioceptive representation of the
upper limb.
b
Although some earlier studies have used this statement to probe real hand
disownership, it could also very well describe illusory ownership over the
rubber hand in participants that experience a vivid RHI where the only
hand they experience as their own is the rubber hand.
READER ET AL.13
positively correlated in Experiment 1 (synchronous con-
dition: r=0.960, asynchronous: r=0.978). However, we
report complementary analyses for peak acceleration in
supplementary material. Peak velocity and reaction time
were compared across conditions using paired ttests
(after checking for normality using the Shapiro–Wilk
test). We also performed Bayesian paired samples ttests,
using a default Cauchy prior with a scale of 0.707, zero-
centred. However, we did not expect any difference in
peak velocity or reaction time between conditions, given
that our previous experiment suggested that effects were
only convincingly observed in relation to the subjective
experience of the real hand disappearing.
The difference in questionnaire statements S2.1–S2.10
response between synchronous and asynchronous condi-
tions was correlated with the difference between
conditions in reaction time and peak velocity. Correlation
was performed using Kendall rank correlations (tau-b)
using an FDR-corrected alpha threshold, as well as
Bayesian Kendall rank correlations (stretched beta prior
width of 1). We predicted that change in statement S2.5
(S1.2 in experiment 1) should correlate with change in
peak velocity, as observed in our previous experiment.
We also expected that other statements assessing the sub-
jective experience of disownership should correlate with
peak velocity.
Finally, we aimed to perform two hierarchical multi-
ple regression analyses. In the first analysis, we planned
to examine how well changes in disownership statements
(S2.5–S2.10) across conditions predicted changes in peak
velocity across conditions, using statements that convinc-
ingly correlated with peak velocity. In a second regres-
sion, we planned to add any other statements that
convincingly correlated with peak velocity. However, no
questionnaire statements convincingly correlated with
peak velocity (see Section 3.2), and so we did not perform
either of these analyses.
3.2 |Results
3.2.1 | Questionnaire
Statistically significant Wilcoxon signed-rank tests
(Figure 5) confirmed that in the synchronous condition
participants felt more like the rubber hand was their
hand (S2.1: W=991, p< 0.001, r=0.119), and more like
the touch they felt was caused by the brush touching the
rubber hand (S2.2: W=1356, p< 0.001, r=0.532), com-
pared with the asynchronous condition, in line with suc-
cessful induction of the RHI. Participants also showed a
statistically significantly reduced disagreement with
statement S2.3 in the synchronous condition, addressing
the potential for agency over the rubber hand (W=681,
p=0.00112, r=0.231).
Participants showed a reduced tendency to disagree
with disownership statements S2.5 (W=708, p< 0.001,
r=0.200), S2.6 (W=606, p< 0.001, r=0.315), S2.8
(W=574, p< 0.001, r=0.352), and S2.9 (W=655,
p< 0.001, r=0.260) in the synchronous condition
compared to the asynchronous condition. This was in
keeping with what we had observed in our disownership
statement in Experiment 1 (S2.5 here, S1.2 in Experiment
1). Furthermore, participants also more strongly agreed
with statement S2.10 (‘it seemed as if the rubber hand
replaced my real hand’) in the synchronous condition
(W=881, p< 0.001, r=0.00508). Though this state-
ment has been considered to capture feelings of dis-
ownership in previous studies (Lane et al., 2017;
Preston, 2013), the wording could also capture the experi-
ence of illusory ownership of the rubber hand in individ-
uals who experience a strong RHI. This latter view is
supported by the similarity in rating scores to ownership
statements S2.1 and referral of touch (S2.2).
There was no statistically significant difference
between the synchronous and asynchronous conditions
regarding the level of agreement to S2.4, addressing the
feeling of having more than one right hand (W=191,
p=0.248, r=0.785). Both the synchronous and asyn-
chronous conditions led to similar denial of this state-
ment, which is in line with statements of this kind being
occasionally used as control statements in the RHI
(e.g., Abdulkarim & Ehrsson, 2016; Preston, 2013). There
was also no statistically significant difference for dis-
ownership statement S2.7, regarding an inability to move
the hand (W=403, p=0.0661, r=0.545), or control
statement S2.11 (W=45, p=0.303, r=0.949).
3.2.2 | Kinematics
The Shapiro–Wilk test indicated a deviation from nor-
mality for the reaction time data, so a Wilcoxon signed-
rank test was used to compare conditions. There was no
significant difference between the synchronous
(mean SE =520 8.42 ms) and asynchronous
(521 7.61 ms) conditions (W=906, p=0.880,
r=0.0232, BF
10
=0.143, max BF
10
=0.997 at Cauchy
prior width 0.0005), in keeping with Experiment 1. There
was no statistically significant difference in peak velocity
between the synchronous (16.0 0.737 cm/s) and asyn-
chronous (16.8 0.728 cm/s) conditions (t(58) =1.60,
p=0.116, g
rm
=0.140, BF
10
=0.471, max BF
10
=1.10 at
Cauchy prior width 0.0681), but we were not able to draw
strong conclusions in favour of the null or alternative
hypothesis from the Bayesian analysis for peak velocity
14 READER ET AL.
(though BF
10
< 0.333 for peak acceleration, see
supporting information).
3.2.3 | Correlation
There were no statistically significant correlations
between change in questionnaire responses across the
synchronous and asynchronous conditions and change in
reaction time or peak velocity across the same
conditions (0.00585 ≤jr
τ
j≤0.163, 0.0915 ≤p≤0.952,
0.170 ≤BF
10
≤0.864) (Table 5). We did not observe a sta-
tistically significant negative correlation between owner-
ship statement S2.1 and peak velocity as observed in
Experiment 1. This was true also for peak acceleration
(r
τ
=0.123, p=0.198, BF
10
=0.426, see Table S1).
Notably, we also failed to replicate the negative cor-
relation between change in disappearance statement
FIGURE 5 Experiment 2 questionnaire results. Coloured circles indicate individual participant values
READER ET AL.15
S2.5 and peak velocity (Figure 6). In addition, most
Bayesian analyses provided greater support for the null
hypothesis rather than the alternative hypothesis. The
only exceptions to this were statements S2.4 and S2.9,
which were positively correlated with change in peak
velocity, though these effects were not statistically signif-
icant and were in the opposite direction to what we
would expect given the results of Experiment 1. We were
not able to draw strong conclusions for either hypothesis
in these instances, though the robustness tests suggested
that there was little convincing support for the alterna-
tive hypothesis even with very narrow zero-centred prior
widths. Similar results were observed when correlating
peak acceleration with S2.4 (r
τ
=0.173, p=0.0816,
BF
10
=1.07) and S2.9 (r
τ
=0.172, p=0.0748,
BF
10
=1.04, see Table S1).
3.2.4 | Combined sample
Kinematics
Given that we did not replicate correlations between peak
velocity and peak acceleration and statements S2.1 and
S2.5, we decided post hoc to combine the datasets from
experiments 1 and 2 for greater statistical power to detect
true effects. There was no statistically significant differ-
ence in peak velocity between the synchronous
(17.7 0.591 cm/s) and asynchronous (18.3 0.644 cm/
s) conditions (t(116) =1.57, p=0.120, g
rm
=0.0870,
BF
10
=0.336, max BF
10
=1.09 at Cauchy prior width
0.0456). To further develop our understanding of non-
significant results, we decided to make the most of an
increased sample size by using equivalence testing
(Lakens, 2017; Lakens et al., 2018). This was done using
the TOST procedure (Lakens, 2017). Equivalence testing
is a frequentist statistical procedure that allows one to
reject the presence of effects as large or larger than a
‘smallest effect size of interest’, ascertaining whether
TABLE 5 Experiment 2 change in illusion measures correlated with change in reaction time and peak velocity (synchronous–
asynchronous)
Reaction time Peak velocity
r
τ
pBF
10
Bayes factor robustness
r
τ
pBF
10
Bayes factor robustness
Max
BF
10
Stretched beta
prior width
Max
BF
10
Stretched beta
prior width
S2.1 0.0387 0.684 0.186 1.00 0.0001 0.103 0.277 0.327 1.02 0.0164
S2.2 0.0296 0.755 0.179 1.00 0.0001 0.0170 0.857 0.172 1.00 0.0001
S2.3 0.0679 0.478 0.225 1.00 0.0001 0.0589 0.538 0.209 1.00 0.0001
S2.4 0.101 0.309 0.318 1.02 0.0092 0.142 0.152 0.590 1.36 0.0654
S2.5 0.0439 0.653 0.191 1.00 0.0001 0.0918 0.347 0.284 1.00 0.0041
S2.6 0.0436 0.651 0.190 1.00 0.0001 0.00585 0.952 0.170 1.00 0.0001
S2.7 0.0984 0.322 0.307 1.01 00092 0.0337 0.734 0.182 1.00 0.0001
S2.8 0.0588 0.544 0.209 1.00 0.0001 0.0284 0.769 0.178 1.00 0.0001
S2.9 0.0104 0.914 0.170 1.00 0.0001 0.163 0.0915 0.864 1.76 0.0827
S2.10 0.0513 0.592 0.199 1.00 0.0001 0.00641 0.947 0.170 1.00 0.0001
FIGURE 6 Scatterplot of change in disownership statement
S2.5 (‘It seemed like my real hand had disappeared’) versus change
in peak velocity (synchronous–asynchronous). Coloured circles
indicate individual participant values
16 READER ET AL.
they are near enough to zero to be effectively equivalent
(a different theoretical framework for assessing ‘null’
results compared to Bayesian analysis). We reasoned that
dz =0.43 could be a feasible smallest effect size of inter-
est, given that this is half of the effect size observed
between synchronous and asynchronous stroking of the
rubber hand in motor-evoked potential amplitude
reported by della Gatta et al. (2016). In the combined
sample this was equivalent to a raw effect size of
1.77 cm/s. We were able to reject the presence of an effect
greater than our smallest effect size of interest (t(116)
=3.09, p=0.00127). Similar results were observed for
peak acceleration (and BF
10
< 0.333, see supporting
information).
Correlation
We correlated the change in peak velocity/acceleration
between conditions with the change in ownership state-
ment S2.1 (S1.1 in Experiment 1) and disownership
statement S2.5 (S1.2 in Experiment 1). For peak velocity,
there was no statistically significant correlation for the
ownership statement, and the Bayes factor suggested that
there was evidence in favour of the null hypothesis
(r
τ
=0.0335, p=0.616, BF
10
=0.139, max
BF
10
=1.00 at stretched beta prior width 0.0001). Similar
results were observed for peak acceleration (see
supporting information). There was also no statistically
significant correlation with the disownership statement,
but we could not draw strong conclusions from the
Bayesian analysis (r
τ
=0.0955, p=0.167, BF
10
=0.383,
max BF
10
=1.28 at stretched beta prior width 0.0256).
BF
10
< 0.333 for the correlation with peak acceleration,
however (see supporting information).
Illusion-susceptible subsets
We also performed one-sided Bayesian paired samples
ttests on the subsets who positively responded to owner-
ship statement S1.1/S2.1 (n=64) and the disappearance
statement S1.2/S2.5 (n=32). As before, we used a default
uninformed Cauchy prior as well as informed normally
distributed priors. We also performed equivalence testing.
For the ownership statement 47% of the subset showed a
reduced peak velocity in the synchronous condition com-
pared with the asynchronous condition (17.9 0.833 ver-
sus 18.3 0.925 cm/s, g
rm
=0.0439). We observed better
evidence in favour of the null hypothesis than the alter-
native hypothesis for the Cauchy prior (BF
10
=0.267,
max BF
10
=1.06 at Cauchy prior width 0.0230), as well
as the normal priors situated on effect size 0.43
(BF
10
=0.254) and 0.85 (0.00712). The equivalence test
also indicated that we could reject the presence of an
effect greater than our smallest effect size of interest
(t(63) =2.72, p=0.00425). Similar results were
observed for peak acceleration (see supporting
information).
For the disappearance statement, 53% of the subset
showed a reduced peak velocity in the synchronous con-
dition compared with the asynchronous condition
(16.5 1.09 versus 17.3 1.14 cm/s, g
rm
=0.121). The
equivalence test indicated that we could not reject
the presence of an effect size that we consider meaningful
(t(32) =1.24, p=0.112). In addition, there was incon-
clusive support for either hypothesis using the Cauchy
prior (BF
10
=0.626, max BF
10
=1.32 at Cauchy prior
width 0.0832) and the normally distributed prior situated
on 0.43 (BF
10
=0.957). However, there was evidence in
favour of the null hypothesis for the effect size situated
on 0.85 (BF
10
=0.101). Similar results were observed for
peak acceleration (see supporting information).
3.3 |General discussion
We examined whether the induction of the RHI has an
influence on rapid index finger abduction. There was lit-
tle evidence that the RHI experimental paradigm inter-
fered with movement. Although both questionnaire data
and proprioceptive drift confirmed the induction of the
RHI in the synchronous condition compared to the asyn-
chronous control, Bayesian analysis generally supported
the absence of an effect on kinematic parameters. There
was little convincing evidence for a correlation between
kinematic parameters and the ratings of sense of owner-
ship over the false hand or proprioceptive drift. Notably,
in Experiment 1, we observed that the degree to which
participants felt as if their real hand had disappeared cor-
related with the acceleration and velocity of their move-
ments. However, we did not replicate this effect in
Experiment 2, and examining a combined dataset did not
allow us to draw any strong conclusions in favour of the
presence or absence of an effect. Overall, these results
suggest the RHI is unlikely to negatively influence the
basic ability to execute simple movements, implying that
motor mechanisms involved in basic movement produc-
tion are unrelated to the changes in multisensory body
representation induced by this illusion.
Regarding the sense of ownership over the rubber
hand, we observed mixed evidence in favour of a correla-
tion between the sense of ownership and movement
velocity and acceleration in Experiment 1, but this was
not replicated in Experiment 2 or when combining the
two experimental datasets. A Bayesian analysis of a large
sample of illusion-susceptible individuals in the com-
bined dataset (n=64) suggested better support for the
null hypothesis than an effect of the rubber hand illusion
on movement. Across all experiments there was little
READER ET AL.17
evidence for an effect of rubber hand ownership on reac-
tion time. These results might suggest that the integration
of a false limb into the central body representation also
results in an integration into the motor system, with little
negative impact on movement initiation or performance.
This would be in keeping with research suggesting that
false limbs might be integrated into action planning
(Heed et al., 2011; Kammers et al., 2010; Newport &
Preston, 2011). However, it is not possible to verify from
which hand the movement was planned in our paradigm:
Index finger abduction can be planned entirely in
somatotopic space (i.e., in terms of muscle groups with-
out any reference to the space surrounding the body),
and the relative digit positions of the two hands
(in somatotopic space) overlap when the movement must
be performed. This is in contrast to the target-directed
actions studied in previous experiments (Heed
et al., 2011; Kammers et al., 2010; Newport et al., 2010;
Newport & Preston, 2011; Zopf et al., 2011), where one
can draw inferences about which hand an action was
planned for (i.e., by examining reach trajectories). How-
ever, even in these previous experiments, effects on
action tended to be small, suggesting that the motor sys-
tem might not be as susceptible to body ownership illu-
sions as conscious perception (see also Matsumiya, 2021).
In addition, our results are at odds with the reduction in
corticospinal excitability reported in illusion-susceptible
individuals by della Gatta et al. (2016), particularly given
that movement force or velocity is related to the dis-
charge of neurons in M1 (Ashe & Georgopoulos, 1994;
Cheney, 1985; Evarts, 1981; Graziano et al., 2002; Jäncke
et al., 2004). It is possible that the change in corticospinal
excitability reported by della Gatta et al. (2016) has little
import to motor behaviour. For example, a disturbance
in motor cortical processing (if it occurs) could be subject
to top-down control when movement is necessary. Whilst
there are inconsistent findings regarding the exact effects
of illusory ownership on the motor system, at the very
least our results suggest that manipulating the sense of
ownership to encompass a new limb does not seem to
have a negative impact on the generation of simple motor
commands.
Concerning proprioceptive drift, we were not able to
draw strong conclusions for the presence or absence of a
systematic relationship with movement. Proprioceptive
drift was only registered in the first experiment, and
although no statistically significant correlation with kine-
matic parameters was observed, the Bayesian analyses
were inconclusive. One possibility is that our use of a
visual reporting task, taken from a vertical distance
30 cm away from the real hand, rather than manual
pointing reduced the size of the recorded drift in the syn-
chronous condition, thus making it more difficult to rule
out or detect effects on movement related to this phe-
nomenon. Indeed, manual proprioceptive drift tasks can
result in values exceeding 6 cm (e.g., Abdulkarim &
Ehrsson, 2016), considerably larger than the values
reported here. Alternatively, it is possible that we might
have observed movement effects linked to proprioceptive
drift had we induced the illusion by stroking the index
finger and using that digit to record perceived hand posi-
tion, because the index finger was the one that was
moved and there is some evidence to suggest that propri-
oceptive drift may be greater in magnitude when
recorded from the stimulated finger (Tsakiris &
Haggard, 2005). However, the middle finger was stroked
to avoid interfering with the motion-tracker and this was
the finger from which the drift measure was recorded,
given the results of Tsakiris and Haggard (2005). Further
work will be necessary to clarify whether proprioceptive
updating and basic movement interact in the RHI.
In Experiment 1, we also observed that the difference
in acceleration and velocity between the synchronous
and asynchronous conditions was correlated with the dif-
ference in the feeling of real hand disappearance between
the conditions. However, we did not replicate this effect
in Experiment 2, nor observe similar correlations with
other statements purported to capture a feeling of dis-
ownership for the real hand. Examining the combined
datasets indicated that we could not draw strong conclu-
sions for or against an influence of a feeling of real hand
disappearance on basic movement. As such, these results
might be in line with the convincing negative findings we
have described regarding the lack of a basic RHI effect on
movement, as well as in terms of rubber hand ownership
ratings. Nevertheless, we will consider two possible
interpretations of the mixed findings regarding the corre-
lation between disownership ratings and movement
parameters.
First, we might consider the effect observed in Experi-
ment 1 to be true, but the small size of the population
effect (and/or low level of population susceptibility to
disownership-related experience) meant we were unable
to detect it in a second sample (i.e., a false negative), as
well as when combining disownership-susceptible sub-
sets from the two experiments. If a true population effect
exists, it may be smaller than that observed in experiment
1 (e.g., for peak velocity r
τ
=0.270, 95% CIs =[0.429,
0.111]). Therefore, we must consider that even our
combined sample of over 100 participants (32 susceptible
to the feeling of disappearance) was too small to reliably
detect an effect.
The existence of such an effect might be in keeping
with the claims of della Gatta et al. (2016), who suggested
that the reduction in corticospinal excitability they
observed during the RHI was due to disownership of the
18 READER ET AL.
real hand during the experiment: ‘body ownership and
the motor system are mutually interactive …an experi-
mental manipulation of the sense of body ownership is
accompanied by a coherent modulation of the motor sys-
tem’, and ‘[if] I believe that the hand is mine, then I
must be ready to use it; if not, then the activity of the
motor system is accordingly down-regulated’(p. 8). They
could not provide direct evidence in favour of this pro-
posal, since the subjective experience of disownership
was not assessed for the group of participants in which
reduced motor-evoked potentials were observed. How-
ever, given that our results suggest that affirmative feel-
ings of disownership are only reported by 30% of
participants, we think it unlikely that this would be a
strong explanation for the effects reported by della Gatta
et al. (2016) and therefore unlikely to be directly related
to the findings reported here. A more reasonable account
for the observed correlations in Experiment 1 could be
related to top-down control of movement under uncer-
tainty, which would not be specific to the feeling of body
disownership. For example, some individuals who experi-
ence the feeling of the real hand ‘disappearing’(or judge
this to be the case) may move more slowly when the cur-
rent state of their real hand appears more uncertain.
Why this would not influence reaction time, however, is
unclear. Given the specific nature of the RHI
(an induction of ownership over a false limb), and that
real hand disownership sensation is often expressed as a
reduction in negative ratings rather than strong positive
phenomenology, it seems like more work is necessary to
confirm the robustness of the effect observed in experi-
ment 1, and what it really tells us about natural
movement.
The second possible explanation for the discrepancy
between Experiments 1 and 2 is that the results of
Experiment 1 were a false positive, and in fact, there is
no population correlation between disownership sensa-
tion and basic movement in the RHI. Any uncertainty
specified in the combined sample analysis could be the
result of bias arising from the (erroneous) Experiment
1 results. This would be in keeping with some previous
findings. For example, Osumi et al. (2018) asked partici-
pants to perform repetitive wrist flexion and extension
movements whilst they observed their hand under differ-
ent levels of visual delay. They found that participants
reported a reduction in the feeling of ownership over
their hand as visual delay increased, and also showed
reduced muscle activity and movement speed. However,
changes in motor output were not correlated with sub-
jective perception, leading the authors to suggest that
different mechanisms may underlie movement execution
and body ownership. The fact that Osumi et al. (2018)
did observe changes in motor output, unlike in our
study, is likely related to the fact that they used a repeti-
tive rather than single movement. In their case, altered
motor output may arise from the distortion of spatial
feedback that occurs as a result of delaying visual feed-
back from a continuous movement (see also Botzer &
Karniel, 2013; Fujisaki, 2012). That is, the required mus-
cle flexion or extension at any one point is uncertain,
since proprioceptive feedback that informs the veridical
position of the limb is in conflict with vision, meaning
that caution may have to be applied to avoid hyper-
flexion or hyperextension. In such a scenario, it is per-
haps unsurprising to observe a reduction in motor
output.
In addition, our own previous work using passive vis-
uoproprioceptive and visuotactile disintegration to
weaken the sense of ownership over the real hand pro-
vided null results (Reader & Ehrsson, 2019). That is, a
reduction in the subjective sensation of ownership over
participants’real hand did not interfere with rapid index
finger abduction, further supporting a distinction
between body ownership and basic movement. However,
we should also note that the feeling of disownership in
the RHI may be qualitatively different to that which
occurs during multisensory disintegration. Feelings of
disownership during multisensory disintegration para-
digms occur due to the incongruence of multisensory
information arising from the real hand (Gentile
et al., 2013; Graham et al., 2014; Kannape et al., 2019;
Lesur et al., 2019; Longo & Haggard, 2009; Newport &
Gilpin, 2011; Newport & Preston, 2011; Osumi
et al., 2018). The visual impression of the (real) hand in
view is perceptually ‘unbound’from tactile and proprio-
ceptive sensation, and this unbinding induces a feeling
that the hand is no longer one’s own. In the RHI, how-
ever, a feeling of real hand disownership may occur as a
consequence of the integration of a false limb into the
central body representation. In a multisensory integra-
tion framework, this means that when proprioceptive
and tactile information from the hidden real hand is per-
ceptually combined with the visual information from the
rubber hand, the participant experiences only the rubber
hand as part of the own body without proprioceptive
awareness of the real hand behind the screen. Notably,
we observed that participants who positively reported the
feeling that their real hand had disappeared tended to
have a stronger feeling of ownership over the rubber
hand than other participants. This suggests that they may
have experienced one coherent multisensory representa-
tion of a hand (the rubber hand) and therefore concluded
that the real hand had been replaced or was no longer a
part of their body, possibly leading to a feeling or judge-
ment of real hand disownership. It may be possible that
such cognitive effects can induce changes in movement
READER ET AL.19
in some individuals, whereas the more explicitly percep-
tual effects of multisensory disintegration do not. This
would not be in keeping with a generalised role of body
ownership in motor control, however.
Whilst our mixed results regarding the sensation of
real hand disownership may be due to either a small or
non-existent population effect, there are limitations of
our experimental paradigm that must also be consid-
ered. Firstly, it is possible that we observe inconsistent
effects due to the relatively low level of susceptibility to
disownership feelings reported by participants. This may
be due to the statements presented in the questionnaire,
though these were drawn from previous studies and the
magnitude of positive response to these subjective feel-
ings seems to be in keeping with previous research
(Lane et al., 2017; Preston, 2013). It appears that a vivid
experience of real hand disownership, as measured by
these commonly used statements, is quite uncommon
during the RHI. To confirm the presence of a movement
effect related to real hand disownership during the RHI
is likely to require a more robust method of inducing
such sensations, or a considerably larger sample size
than presented here. Alternatively, the statements used
to address feelings of disownership may fail to ade-
quately capture the proposed phenomenon, or may be
misunderstood by some individuals. Certainly there has
been some discussion regarding whether agreement
with disownership-related statements in the RHI truly
reflects the experience of the participant, or rather what
they ‘judge’to be the case, that is, post-perceptual pro-
cesses such as conscious reflection (de Vignemont, 2011;
Lane et al., 2017). Different interpretations of the illu-
sion statements could result in a smaller likelihood of
capturing any true effect, or alternatively increasing the
chance of observing effects related to some unknown
variable.
Another possible limitation of our experimental para-
digm and a possible explanation for our null results is
that participants may have had too much time to prepare
for movement following the illusion (between 0.2 and
2 s), potentially reducing the influence of any illusory
sensation (and also resulting in a general lack of reaction
time effects). However, the after-effects of limb owner-
ship illusions and full-body ownership illusions tend to
be long-lasting, and can influence behaviour for an
extended period once multisensory stimulation has fin-
ished and the artificial body is obscured (Bergouignan
et al., 2014; Guterstam et al., 2015; Perepelkina
et al., 2018; Van der Hoort & Ehrsson, 2016). The RHI
may be maintained for at least 20 s after brushstrokes are
applied to the real and the rubber hands (Abdulkarim
et al., 2021), and activity in areas related to the multisen-
sory representation of the hand such as the ventral
premotor cortex show sustained activity for at least
1300 ms following tactile stimulation (Guterstam
et al., 2019).
To conclude, the induction of the RHI may not inter-
fere with rapid index finger abduction, suggesting that
passive manipulations of multisensory congruence or
manipulations of body ownership do not necessarily
induce changes in basic motor behaviour. However,
more research is needed to conclusively determine
whether real hand ‘disownership’during the RHI may
reduce the speed with which simple finger movements
are performed, as our results were inconclusive in this
regard. In general, our results speak against a strong
functional effect of body ownership in basic movement
(i.e., simply changing the position of the body, without
reference to external objects or agents), at least for very
simple tasks. Given that body ownership might support
interaction with the environment through the segrega-
tion of self and world, there appears to be little a priori
justification for a role of body ownership in purely self-
relevant motor processing. Simple movements like an
index finger abduction are unlikely to require spatial
coordinate transformations, a multisensory representa-
tion of the muscle in question, or information about the
location of the limb in external space. Activation of a
single muscle is likely to be performed independently of
the sense of body ownership, in our case effectively
induced through the supplementary motor area signal-
ling the cortical territory of M1 that innervates the first
dorsal interosseous, a process sufficiently supported by
sensory information signalling the current postural state
of the body (e.g., from muscle spindles) (Naito
et al., 2016; Proske & Gandevia, 2012). This would be
consistent with theoretical models of body ownership
that consider the phenomenon as a multisensory percep-
tion of the body separate from action planning, motor
control, or the neural state of the primary motor cortex
(Chancel & Ehrsson, 2020; Ehrsson, 2020; Kilteni
et al., 2015; Samad et al., 2015). Finally, from an applied
perspective, these results are encouraging as they suggest
that the embodiment of technology and artificial limbs
(Collins et al., 2017; Makin et al., 2017; Niedernhuber
et al., 2018; Pazzaglia & Molinari, 2016) through multi-
sensory mechanisms may not impair the users’ability to
generate rapid movements, which supports the potential
development of efficient motor control with embodied
technology.
ACKNOWLEDGEMENTS
This study was funded by The Swedish Research Council
(Distinguished Professor grant), Göran Gustafssons
Stiftelse, and the European Research Council advanced
grant SELF-UNITY (to H.H.E.).
20 READER ET AL.
CONFLICT OF INTEREST
The authors declare that they have no conflict of interest.
AUTHOR CONTRIBUTIONS
A.T.R. and H.H.E. designed the experiments. A.T.R. and
V.S.T. collected and analysed the data. All authors con-
tributed to writing the manuscript.
PEER REVIEW
The peer review history for this article is available at
https://publons.com/publon/10.1111/ejn.15444.
DATA AVAILABILITY STATEMENT
Data and JASP outputs for planned analyses are available
from the Open Science Framework (https://doi.org/10.
17605/OSF.IO/NYHZQ).
ORCID
Arran T. Reader https://orcid.org/0000-0002-0273-6367
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SUPPORTING INFORMATION
Additional supporting information may be found in the
online version of the article at the publisher’s website.
How to cite this article: Reader, A. T., Trifonova,
V. S., & Ehrsson, H. H. (2021). Little evidence for
an effect of the rubber hand illusion on basic
movement. European Journal of Neuroscience,
1–24. https://doi.org/10.1111/ejn.15444
24 READER ET AL.
