1: Exp Brain Res. 2004 Sep 10 [Epub ahead of print]
Keeping with the beat: movement trajectories contribute to movement timing.
Balasubramaniam R, Wing AM, Daffertshofer A.
Behavioural Brain Sciences Centre, School of Psychology, University of
Birmingham, B15 2TT, Edgbaston, UK.
Previous studies of paced repetitive movements with respect to an external beat
have either emphasised (a) the form of movement trajectories or (b) timing
errors made with respect to the external beat. The question of what kinds of
movement trajectories assist timing accuracy has not previously been addressed.
In an experiment involving synchronisation or syncopation with an external
auditory metronome we show that the nervous system produces trajectories that
are asymmetric with respect to time and velocity in the out and return phases of
the repeating movement cycle. This asymmetry is task specific and is independent
of motor implementation details (finger flexion vs. extension). Additionally, we
found that timed trajectories are less smooth (higher mean squared jerk) than
unpaced ones. The degree of asymmetry in the flexion and extension movement
times is positively correlated with timing accuracy. Negative correlations were
observed between synchronisation timing error and the movement time of the
ensuing return phase, suggesting that late arrival of the finger is compensated
by a shorter return phase and conversely for early arrival. We suggest that
movement asymmetry in repetitive timing tasks helps satisfy requirements of
precision and accuracy relative to a target event.
PMID: 15365663 [PubMed - as supplied by publisher]
2: Exp Brain Res. 2004 Sep 4 [Epub ahead of print]
Perceived reachability: the roles of handedness and hemifield.
Fischer MH.
Department of Psychology, University of Dundee, DD1 4HN, Dundee, Scotland, UK.
The impact of reaching experience on the ability to predict one's own reaching
range was investigated. Left- and right-handed participants made verbal
estimates about the reachability of a target object for both arms in ipsilateral
and contralateral frontal space. There was a significant overestimation bias in
both groups and for both hands. The overestimation bias increased with the
target object's eccentricity in contralateral space. The implications of these
findings for models of motor control and motor imagery are discussed.
PMID: 15351926 [PubMed - as supplied by publisher]
3: Neural Comput. 2004 Oct;16(10):2021-40.
Different predictions by the minimum variance and minimum torque-change models
on the skewness of movement velocity profiles.
Tanaka H, Tai M, Qian N.
Center for Neurobiology and Behavior and Department of Physiology and Cellular
Biophysics, Columbia University, New York, NY 10032, USA.
We investigated the differences between two well-known optimization principles
for understanding movement planning: the minimum variance (MV) model of Harris
and Wolpert (1998) and the minimum torque change (MTC) model of Uno, Kawato, and
Suzuki (1989). Both models accurately describe the properties of human reaching
movements in ordinary situations (e.g., nearly straight paths and bell-shaped
velocity profiles). However, we found that the two models can make very
different predictions when external forces are applied or when the movement
duration is increased. We considered a second-order linear system for the motor
plant that has been used previously to simulate eye movements and single-joint
arm movements and were able to derive analytical solutions based on the MV and
MTC assumptions. With the linear plant, the MTC model predicts that the movement
velocity profile should always be symmetrical, independent of the external
forces and movement duration. In contrast, the MV model strongly depends on the
movement duration and the system's degree of stability; the latter in turn
depends on the total forces. The MV model thus predicts a skewed velocity
profile under many circumstances. For example, it predicts that the peak
location should be skewed toward the end of the movement when the movement
duration is increased in the absence of any elastic force. It also predicts that
with appropriate viscous and elastic forces applied to increase system
stability, the velocity profile should be skewed toward the beginning of the
movement. The velocity profiles predicted by the MV model can even show
oscillations when the plant becomes highly oscillatory. Our analytical and
simulation results suggest specific experiments for testing the validity of the
two models.
PMID: 15333205 [PubMed - indexed for MEDLINE]
4: Exp Brain Res. 2004 Aug 14 [Epub ahead of print]
Between-trial inhibition and facilitation in goal-directed aiming: manual and
spatial asymmetries.
Tremblay L, Welsh TN, Elliott D.
University of Toronto, Toronto, Canada.
Three experiments were conducted with right-handed participants to examine
between-trial inhibition and facilitation effects in goal-directed aiming.
Participants were required to execute rapid left-hand or right-hand aiming
movements upon illumination of a target light in left or right space. Thus, from
trial to trial, participants executed movements to either the same target
location or a different target location with the either same hand or the other
hand. Our reaction time results indicated that participants were particularly
slow in initiating their movements when they were required to return to the same
target location with the other hand. This was especially the case when the right
hand was required to move to a target just occupied by the left hand. For both
reaction time and movement time the right hand but not the left hand exhibited
an advantage when it was required to perform the same movement two times in a
row. Taken together these results suggest that inhibition of return, in a
target-target paradigm, is more associated with the particular spatial location
of the target than the organization of a specific movement to that location.
Moreover, the between-trial facilitation observed for the right hand may reflect
the ability of the left cerebral hemisphere to maintain an already parameterized
motor program over a short intertrial interval.
PMID: 15316705 [PubMed - as supplied by publisher]
5: Exp Brain Res. 2004 Aug 12 [Epub ahead of print]
The time course for kinetic versus kinematic planning of goal-directed human
motor behavior.
Vesia M, Vander H, Yan X, Sergio LE.
School of Kinesiology and Health Science, Center for Vision Research, York
University, 4700 Keele Street, M3 J 1P3, Toronto, Ontario, Canada.
The present psychophysical study compares motor planning during goal-directed
reaching movements and isometric spatial force generation. Our objective is to
characterize the extent to which the motor system accounts for the biomechanical
details of an impending reach. One issue that the nervous system must take into
account when transforming a spatial sensory signal into an intrinsic pattern of
joint torques is that of limb dynamics, including intersegmental dynamics and
inertial anisotropy of the arm. These will act to displace the hand away from a
straight path to an object. In theory, if the nervous system accounts for
movement-related limb dynamics prior to its initial motor output, early force
direction for a movement will differ from an isometric force to the same spatial
target. Alternatively, biomechanical details of motor behavior may be
implemented into the motor act following its initiation. Limb position and force
output at the wrist were recorded while subjects displaced a cursor to targets
viewed on a computer monitor. To generate isometric forces, a magnetic brake
held a mechanical linkage supporting the arm in place. Subjects were cued to
displace the cursor by using either isometric force or limb movement. On random
trials, a movement was cued but an isometric force was unexpectedly required.
Results show that there is not a significant directional difference in the
initial force trajectory when planning a movement versus planning an isometric
force. These findings suggest that the motor system may initially use a coarse
approximation of movement-related limb dynamics, allowing for the refinement of
the motor plan as the movement unfolds.
PMID: 15309357 [PubMed - as supplied by publisher]
6: Exp Brain Res. 2004 Aug 11 [Epub ahead of print]
Dynamics of learning and transfer of muscular and spatial relative phase in
bimanual coordination: evidence for abstract directional codes.
Temprado JJ, Swinnen SP.
UMR 6152 "Mouvement et Perception", Universite de la Mediterranee et CNRS,
Faculte des Sciences du Sport, 163 Avenue de Luminy, Marseille, France.
The present study addressed whether the timing of muscle activation and the
relative direction of limb movements are dissociable constraints that may affect
learning and transfer of bimanual coordination patterns, either independently or
in combination. Subjects were assigned to two experimental groups in which the
to-be-learned muscular phasing (135 degrees ) was either practiced with 45
degrees (i.show $132#e., predominantly isodirectional) or 135 degrees (i.show
$132#e., predominantly nonisodirectional) of spatial relative phase (RP) across
2 days of practice. Prior to, during, and following practice, probe tests were
held in which various relative phasing patterns were administered to assess
transfer of learning. Converging evidence was obtained that the relative
direction of moving limbs prominently constrained transfer of learning rather
than muscular relationships. Acquisition of a specific pattern resulted in
spontaneous positive transfer of learning to a new coordination pattern having
the same spatial RP but not to a pattern with a different spatial RP,
irrespective of muscular phasing relationships. In summary, the present results
suggest that learning and transfer of coordination patterns is mediated by
abstract directional codes that become part of the memory representation for
bimanual coordination.
PMID: 15309354 [PubMed - as supplied by publisher]
7: Exp Brain Res. 2004 Jul 30 [Epub ahead of print]
Action-induced blindness with lateralized stimuli and responses.
Musseler J, Wuhr P, Danielmeier C, Zysset S.
Institut fur Arbeitsphysiologie, Universitat Dortmund, Ardeystr. 67, 44139,
Dortmund, Germany.
Previous dual-task studies showed that the selection and/or execution of a
response interfere with concurrent visual encoding (action-induced blindness).
Four experiments examined how the lateralization of stimuli and responses might
affect action-induced blindness. Participants responded to tones (S1) by
pressing keys with the left or right hand (R1), and simultaneously identified
stimuli (S2) presented to the left or right visual field. Results revealed a
complex pattern of cross-talk effects between response preparation and visual
encoding. Firstly, preparing a response generally impaired concurrent visual
encoding. Secondly, action-induced blindness was equally present for
ipsilaterally and contralaterally presented stimuli. Thirdly, response
preparation facilitated processing of visual stimuli at ipsilateral locations,
probably a case of action-centered attention. Finally, the facilitatory effect
of R1-S2 correspondence on visual encoding was complemented by a S2-R1
correspondence effect on response execution. Thus, acting while seeing can have
both beneficial and detrimental effects on identification performance at the
same time.
PMID: 15289962 [PubMed - as supplied by publisher]