2013. Vol.4, No.12, 1004-1007
Published Online December 2013 in SciRes (
Open Access
Transfer of Visuomotor Adaptation to Unpractised Hands
and Sensory Modalities
Otmar Bock1, Gerd Schmitz2
1Institute of Physiology and Anatomy, German Sport University Cologne, Cologne, Germany
2Institute of Sports Science, Leibniz University Hannover, Hannover, Germany
Received September 18th, 2013; revised October 23rd, 2013; accepted November 21st, 2013
Copyright © 2013 Otmar Bock, Gerd Schmitz. This is an open access article distributed under the Creative
Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited. In accordance of the Creative Commons Attribution License all
Copyrights © 2013 are reserved for SCIRP and the owner of the intellectual property Otmar Bock, Gerd
Schmitz. All Copyright © 2013 are guarded by law and by SCIRP as a guardian.
A recent model (Bock, 2013) predicts that sensorimotor adaptation, achieved while pointing at visual tar-
gets, will transfer fully to acoustic targets. The model further predicts that visual-to-acoustic transfer is
not diminished even if the left and right arms have adapted to a different distortion. To scrutinize these
predictions, we asked subjects to point at visual targets with their right hands under a +30 deg rotation of
visual feedback (group “single”), or alternately, with their right hands under a +30 deg and with their left
hands under a 30 deg rotation of visual feedback. Aftereffects were registered for each hand and for vis-
ual as well as acoustic targets, in counterbalanced order. We found that acoustic aftereffects were only
about 66% of visual ones, which violates the first prediction and calls for an amendment of the model. We
further found that acoustic aftereffects were of similar magnitude in both groups, which supports the sec-
ond prediction. Finally, we observed an intermanual transfer of only about 29%. These findings suggest
that unpractised acoustic inputs are weighted somewhat lower than practised visual ones, and that outputs
to the unpractised left hand are weighted substantially lower than those to the practised right hand.
Keywords: Sensorimotor Adaptation; Motor Learning; Intermanual; Intersensory; Transfer
Sensorimotor adaptation is not limited to the task by which it
was established, but rather can transfer to unpractised motor
systems (Cohen, 1973; Cotti, Guillaume, Alahyane, Pélisson, &
Vercher, 2007), new target locations (Bock, 1992; Malfait,
Gribble, & Ostry, 2005) and different distortions (Thomas &
Bock, 2010). These findings should not be taken as evidence
that adaptation is achieved by one common process, shared by
all motor systems, target locations and distortions. Rather, mul-
tiple adaptive processes seem to exist since subjects can con-
currently adapt to two distinct distortions, administered in de-
pendence on the arm used (Prablanc, Tzavaras, & Jeannerod,
1975; Thomas & Bock, 2012), on target location (Alahyane,
2004; Woolley, Tresilian, Carson, & Rick, 2007) or on contex-
tual cues (Wada et al., 2003). We are thus left with the puzzling
fact that adaptation can transfer from one arm to the other—as
if both arms shared a common adaptive process— whilst both
arms also can adapt differently—as if each had its own adaptive
A model has recently been proposed to explain this apparent
discrepancy. As shown in Figure 1, it stipulates that multiple
sensory modalities serve as inputs to multiple adaptive mecha-
nisms which, in turn, send their outputs to multiple motor sys-
tems via a context-dependent switch; the outputs are differently
weighted for practised and for unpractised motor systems.
According to this model, single-limb practice doesn’t affect the
switch position and thus yields transfer of adaptation, while
two-limb practice changes the switch position in dependence on
the currently active motor system and thus yields limb-specific
Figure 1.
Conceptual model of sensorimotor adaptation. Sensory inputs from
different modalities (I1, I2, …) are transformed by multiple adaptive
mechanisms, and their outputs are connected by a context-dependent
switch to various motor outputs (O1, O2, …). The connections are
weighted differently (W1, W2, …) depending on whether the motor
system is practised or not. Reprinted with modifications from (Bock,
The present study scrutinizes two predictions of the pub-
lished model. First, practised and unpractised motor systems
are assigned by different weights, while practised and unprac-
tised sensory modalities are not; if so, adaptation should trans-
fer partially between arms but fully between targets from dif-
ferent modalities. It has indeed been shown that adaptation with
visual targets transfers to acoustic targets (Zwiers, van Opstal,
& Paige, 2003) and that aftereffects are equal in both modalities
(Kagerer & Contreras-Vidal, 2009); however the latter study
always tested acoustic targets first and visual targets thereafter,
so that a possible visual advantage might have dissipated by the
time of testing. To overcome this problem, we now test both
arms and modalities in counterbalanced order.
According to the second prediction of the published model,
both arms can concurrently adapt to different distortions with-
out interference, and this dual adaptation should again transfer
fully between sensory modalities. The first part of this predict-
tion has been confirmed in literature (Bock, Worringham, &
Thomas, 2005; Prablanc et al., 1975), and we now address the
second part.
25 male and 23 female subjects aged 22.0 1.6 years parti-
cipated after signing their informed consent to this study, which
was approved in advance by the first author’s Ethics Committee.
Subjects were right-handed, healthy, and had no prior experi-
ence with adaptation research. As shown by the inset of Figure
1, subjects faced an opaque horizontal panel with a wooden
dowel protruding downwards underneath their chin. Targets
were presented on the upper surface of the panel, along a semi-
circle of 36 cm radius around the dowel. They were presented
in balanced order at 30, 18, and 6 deg about straight-ahead,
either as light dots of 1.5 cm radius, or as sounds (mix of 0.45,
1.35, 2.30 and 3.20 kHz) from loudspeakers of 1.5 cm radius;
the loudspeaker array was hidden from view by a fabric screen.
Subjects pointed with their index fingertip underneath the panel,
moving from the dowel towards each target where the radial
response component was stopped by a semicircular barrier.
Subjects then moved the finger along that barrier until it was
aligned with the target. They couldn’t see their arm and hand
because of the opaque panel, but index fingertip position was
registered by the Fastrak® system (resolution 1 mm and 17 ms),
and could be displayed as a cursor on the upper surface of the
panel to provide real-time visual feedback.
The experiment was subdivided into pointing episodes of 45
s duration (or about 25 responses), separated by rest breaks of 5
s. Each experiment started with six baseline episodes. In the
first two, subjects pointed with their right hand at visual targets
and received veridical visual feedback. In the remaining four
baseline episodes, they pointed without visual feedback at vis-
ual targets with their right hand (VR), at visual targets with
their left hand (VL), at acoustic targets with their right hand
(AR), and at acoustic targets with their left hand (AL); the order
of these episodes was counterbalanced across subjects. In the
subsequent adaptation episodes, subjects pointed at visual tar-
gets under rotated visual feedback. One half of them formed
group “single”, which used their right hand under a +30 deg
rotated feedback. The other half formed group “dual”, which
alternately used their right hand under a +30 deg rotated feed-
back, and their left hand under a 30 deg rotated feedback.
Group “single” performed 20 and group “dual” 40 adaptation
episodes, i.e., there were 20 adaptation episodes per hand in
both groups. The experiment concluded with four aftereffect
episodes, which replicated VR, VL, AR and AL, again in coun-
terbalanced order.
The registered finger position data were analysed by an in-
teractive computer routine which determined the directional
error of each response, defined as angle between target and
cursor direction 166 ms after movement onset. This quantifies
the feedforward component of motor control without confound-
ing it with feedback-based error corrections, which emerge later
during the response. For graphical presentation and statistics,
we calculated the mean error of each adaptation episode minus
that of the second baseline episode, and the mean errors of each
aftereffect episode minus that of the pertinent baseline episode.
To facilitate comparisons, data yielded with the left hand of
group “dual” were sign-reversed. The outcome was submitted
to analyses of variance (ANOVAs) with Greenhouse-Geyser
corrections if variances were unequal.
Figure 2 illustrates the errors of group “single” and “dual”
throughout the adaptation block. For clarity, the left hand of
group “dual” is plotted in same episodes as the right hand al-
though the data actually came from separate, interleaved epi-
sodes. ANOVA with the between-factor Task (single, dual right,
dual left) and the within-factor Episode (1, 2, …, 20), yielded
significance only for Episode (F(19,1292) = 13.15, p < 0.001).
The aftereffects of both groups are summarized in Figure 3.
ANOVA with the between-factor Group (single, dual) and the
within-factors Hand (R, L) and Modality (V, A) yielded signi-
ficance for Group (F(1,46) = 5.83; p < 0.05), Hand (F(1,46) =
8.46; p < 0.01) and Group*Hand (F(1,46) = 64.80; p < 0.001):
aftereffects with the right hand reached a similar magnitude in
both groups, but only 29% of that magnitude with the unprac-
tised left hand of group “single”; the practised left hand of
group “dual” even showed slightly larger aftereffects than the
right hand. Furthermore, ANOVA yielded significance for
Modality (F(1,46) = 15.39; p < 0.001): aftereffects with acous-
tic targets were only 66% of those with visual targets. No other
interactions reached significance.
The present study evaluates the transfer of sensorimotor ad-
aptation to an unpractised limb and to an unpractised sensory
modality, to scrutinize a recently published conceptual model
(Bock, 2013). Our discussion will focus on the observed after-
effects rather than on the time-course of adaptation, since after-
effects are thought to be a pure indicator of sensorimotor re-
calibration while the time-course of adaptation may also reflect
workaround strategies (McNay & Willingham, 1998; Redding,
1996; Werner & Bock, 2007).
The above model predicts that inputs from different sensory
modalities are weighted equally, which implies that adaptation
will fully transfer between modalities. This, however, was not
the case in our study: following adaptation with visual targets,
the magnitude of aftereffects with acoustic targets was only
66% of that with visual ones. The model therefore must be
amended; specifically, if the practised visual modality in our
study is given a weight of 1.00, then the unpractised acoustic
modality should obtain a weight of only 0.66. Further work is
Open Access 1005
Open Access
Figure 2.
Above-baseline errors during the adaptation block in groups “single” and “dual”. VR and VL stand for visual rotation while using the right and left
hand, respectively, with the type of rotation indicated in parentheses. Left-hand errors are inverted to facilitate comparisons. Symbols represent the
across-subject means for each episode, and bars the corresponding standard errors. The inset is a sketch of the experimental setup: subjects pointed
underneath an opaque panel, from a wooden dowel (D) towards visual (V) or acoustic targets (A) which were located along a semicircle around D; the
hardware for delivery of acoustic stimuli was concealed from view, but one stimulus location is made visible in the sketch.
Figure 3.
Aftereffects in group “single” and “dual”. Histograms represent across-
subject means, and bars the corresponding standard errors. Left-hand
data are inverted to facilitate comparisons. VR: visual targets and right
hand, VL: visual targets and left hand, AR: acoustic targets and right
hand, AL: acoustic targets and left hand.
needed to find out whether this lower weight is due to the lack
of practise, or rather to the poorer localization of acoustic com-
pared to visual targets.
Our finding, that input weights differ between sensory mo-
dalities, contrasts with the outcome of an earlier study, which
found visual and acoustic aftereffects of similar magnitude
following adaptation with visual targets (Kagerer & Contreras-
Vidal, 2009). We suggest that this discrepancy is due to an
artefact of fixed-order testing in the earlier study: acoustic af-
tereffects were always tested first and visual aftereffects second,
such that the latter might already have declined by the time of
The published model further predicts that there will be no
interference between sensory modalities when both arms adapt
to different distortions, which was indeed confirmed by our
data: the difference between visual and acoustic aftereffects
was comparable for both hands and groups. This might seem
trivial at a first glance; note, however, that the left-hand data of
group “dual” was sign-inversed for graphical presentation and
statistical analysis. Without that transformation, it would be
more obvious that visual and acoustic aftereffects of group
“dual” were positive with the right hand, but both were nega-
tive with the left hand. Thus, differential adaptation of the right
hand to +30 deg rotation and of the left hand to 30 deg rota-
tion, achieved with visual targets, led to an unabridged differ-
ential transfer to acoustic targets.
As an additional outcome of the present study, we now can
apply specific values to the output weights of the adaptation
model. Given the different magnitude of aftereffects with the
right and left hand of group “single”, a weight of 1.00 for the
practised right hand corresponds to a weight of 0.29 for the
unpractised left hand. However, this outcome can’t be general-
ized across all adaptation paradigms since different earlier
studies yielded substantially different magnitudes of interma-
nual transfer, depending e.g. on the distribution of practise
(Taub & Goldberg, 1973) and on the provision of continuous
versus terminal feedback (Cohen, 1967).
Summing up, the present study allowed us to confirm, modi-
fy and enumerate some aspects of a conceptual model of sen-
sorimotor adaptation. We plan to scrutinize other aspects in
future work.
This study was supported by the German Research Council
DFG (Bo 649/8) and by the German Federal Ministry for Re-
search and Technology (50WB9942). Responsibility for the
contents rests with the authors.
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