Exp Brain Res (2011) 214:215–224
DOI 10.1007/s00221-011-2822-9RESEARCH ARTICLE
Congruent visual and proprioceptive information results
in a better encoding of initial hand position
Louis-Nicolas Veilleux · Luc Proteau
Received: 14 March 2011 / Accepted: 29 July 2011 / Published online: 12 August 2011
© Springer-Verlag 2011
Abstract Goal-directed movements performed in a
virtual environment pose serious challenges to the central
nervous system because the visual and proprioceptive rep-
resentations of one’s hand position are not perfectly con-
gruent. The aim of the present study was to determine
whether the vision of one’s hand or upper arm, compared
with that of a cursor representing the tips of one’s index
Wnger and thumb, optimizes the planning and modulation of
one’s movement as the cursor nears the target. The partici-
pants performed manual aiming movements that diVered by
the source of static visual information available during
movement planning and the source of dynamic information
available during movement execution. The results revealed
that the vision of one’s hand during the movement planning
phase results in more eYcient online control processes than
when the movement planning was based on a virtual repre-
sentation of one’s initial hand location. This observation
was seen regardless of the availability of online visual feed-
back during movement execution. These results suggest
that a more reliable estimation of the initial hand position
results in more accurate estimation of the position of the
cursor/hand at any one time resulting in more accurate
online control.
Keywords Movement planning · Movement control ·
Manual aiming · Proprioception · Visual feedback ·
Virtual environments
Introduction
Every day, most individuals perform reaching movements
either to touch the “start” button of their computer or to
move a cursor on a computer screen to reach an icon. In
both cases, one must Wrst determine the initial location of
his or her hand or that of the cursor and target. The central
nervous system (CNS) appears to use this information to
determine a movement vector and issue a series of motor
commands (Ghilardi et al. 1995; Gordon et al. 1994b). As
the movement progresses toward the target, aVerent infor-
mation ensures the correction of planning errors resulting
from any misperceptions of the hand/cursor (Vindras et al.
1998, 2005) or the target localization (Desmurget et al.
2005; Prablanc and Martin 1992), any biomechanical fac-
tors aVecting initial limb inertia (Gordon et al. 1994a;
Mackrous and Proteau 2007), or any noise in the planning
(Meyer et al. 1988; Schmidt et al. 1979) and execution pro-
cesses (van Beers et al. 2004).
Although apparently very similar to a manual aiming
task, the cursor-aiming task described above poses some
interesting challenges to the CNS. First, in a manual aiming
task, the seen and felt positions of one’s limb provide
direct, comparable information to the CNS concerning the
starting point of the movement. This correlation does not
occur in a cursor-aiming task for which the seen position of
the cursor might represent conditions such as the tip of the
index Wnger or the position of a computer mouse. Veilleux
and Proteau (2011) recently showed that seeing one’s upper
limb prior to movement initiation resulted in smaller end-
point bias and variability than when the initial position of
one’s limb was represented by a cursor. Interestingly, the
smaller endpoint variability observed in the former condi-
tion largely resulted from a sharp reduction in the move-
ment variability between the peak deceleration and end of
L.-N. Veilleux · L. Proteau (&)
Département de Kinésiologie, Université de Montréal,
C.P. 6128, Succursale Centre Ville,
Montréal, QC H3C 3J7, Canada
e-mail: luc.proteau@umontreal.ca
L.-N. Veilleux
e-mail: lnveilleux@shriners.mcgill.ca123

216 Exp Brain Res (2011) 214:215–224the initial impulses of the movement. Veilleux and Proteau
proposed that tight coupling of the visual and propriocep-
tive information concerning the origin of the movement
vector results in an accurate and reliable internal represen-
tation of one’s hand on the starting base. In turn, as the
starting position of the hand becomes more accurately deW-
ned, the CNS can better predict its course toward the target,
leading to a more eYcient modulation of the movement as
the hand nears the target (Bourdin et al. 2006; Desmurget
and Grafton 2003).
The aim of the present study was to determine what
source of visual information prior to movement execution
optimizes the modulation of one’s movement when visual
feedback is either available or unavailable as the hand nears
the target: the vision of just the hand or the vision of the
entire arm? In addition to its theoretical importance, this
question is of interest because a better understanding of
how visual and proprioceptive feedback are optimally com-
bined could lead to the optimization of virtual and video
systems that are used in diVerent learning and rehabilitation
settings.
One may only need to see his/her hand at the starting
position to optimize movement planning and control these
processes because the felt and seen position of the move-
ment vector origin are congruent. Graziano et al. (2000)
reported the presence of bimodal neurons in the primate
posterior parietal cortex that receive both visual and propri-
oceptive input regarding the position of the arm. These neu-
rons discharged when the initial position of the monkey
upper limb was represented by a fake stuVed arm posi-
tioned in a natural anatomical position but not when the
upper limb was represented by paper triangles. One possi-
ble explanation is that these bimodal neurons do not dis-
charge when the position of one’s hand is represented by a
cursor, resulting in a suboptimal integration of visual and
proprioceptive information relative to the position of the
hand. Alternatively, the optimization of movement plan-
ning and control might not be due to the vision of the hand
itself but rather the vision of the entire upper limb. With
respect to the latter idea, Sober and Sabes (2005) showed
that the availability to the participant of a virtual represen-
tation of his/her arm gives more weight to the visual infor-
mation for the movement planning and control processes
than does the representation of hand position by a cursor.
Thus, the representation of the hand/arm position by a cur-
sor on the computer screen may result in the loss of relevant
visual information relative to arm conWguration.
To fulWll the aim of this study, participants performed
reaching movements toward one of three visual targets.
Prior to movement onset, participants in the Wrst group had
a visible cursor on the starting base without any other addi-
tional visual feedback relative to the hand or arm position.
Participants in the second group could see the position of
both the cursor and their hand, but not that of their forearm
and arm. In contrast, the participants in the third group
could see both the cursor and their entire upper limb prior
to movement onset. For each group, the cursor remained
visible or was occluded after the movement initiation was
detected. The results could then be used to determine
whether the presumed more accurate/reliable representation
of one’s hand when it is visible at the starting position pro-
duces a more eYcient modulation of the latter part of one’s
movement.
Method
Participants
Forty-two undergraduate students, aged between 20 and
25 years old, were recruited in the Département de kinésiol-
ogie from the Université de Montréal. The participants had
no previous experience with these experimental tasks. All
participants reported normal or corrected to normal vision.
The Health Sciences Ethics Committee of the Université de
Montréal approved this study.
Task and apparatus
The participants had to perform a manual aiming task in
which they moved a computer’s mouse-like device on a
horizontal surface from a Wxed starting position toward
three possible targets. The apparatus (Fig. 1) consists of a
table, two-degree-of-freedom manipulandum, computer
screen, headrest, semi-reXecting mirror, cardboard, and
light source.
Each participant sat close to the table so that his or her
body rested along its leading edge. The tabletop was cov-
ered by a piece of Plexiglas over which the manipulandum
and a starting base were aYxed. The manipulandum con-
sisted of two pieces of rigid Plexiglas (43 cm) joined at one
end by an axle. One of its free ends was Wtted with a second
axle encased in a stationary base that was aYxed to the
tabletop. The other free end was Wtted with a small vertical
shaft (length: 3 cm, radius: 1 cm), hereafter called “the sty-
lus”, that could be easily gripped by the participant. The
starting base consisted of a thin strip of Plexiglas glued to
the tabletop that was parallel to the leading edge of the table
and had a small indentation on one of its faces. The inden-
tation was located directly in line with the lateral center of
the computer screen and the participant’s midline. This
indentation enabled the participants to easily position the
stylus at the start of each trial. Each axle of the manipulan-
dum was Wtted with a 13-bit optical shaft encoder (U.S.
Digital, model S2-2048, sampled at 500 Hz, angular accu-
racy of 0.0439°) that enabled the displacement of the stylus123