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Presentation Start/End Time:
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Sunday, Nov 16, 2008, 11:00 AM -12:00 PM
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Authors:
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*A. KARNIEL, L.
BOTZER;
Biomed. Engin, Ben-Gurion Univ.
Negev, Beer Sheva, Israel
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A reaching movement is an elementary motor task extensively
studied and measured in numerous laboratories around the world, with important
scientific and clinical applications. Since a fast reaching movement is
typically considered a ballistic movement, namely produced in feedforward
open loop control, at least at the initial stage of the movement, the key
features of such a movement are its initiation time and the initial speed
profile. In this study we propose a novel method to extract the movement
onset time and the speed profile during the commencement of the movement.
The minimum acceleration criterion with constraints (MACC) was recently
proposed as an underlying principle for optimal trajectories of arm reaching
movements. [Ben-Itzhak and Karniel, Neural Computation, 20(3):779-812,
2008]. The MACC derived trajectory consists of three parts which initially
starts with a constant jerk (third time derivative of position) .
Our method assumes that the arm is initially stationary and then moves with
constant jerk towards the new position. Hence, our goal is to detect when the
movement diverts from a constant position, and what the value of the constant
jerk is. We used a 100mSec search window in which the piecewise polynomial
model described above was fitted numerically. The minimal fitting error was
used to detect the movement onset as well as the initial jerk. Verification
of the method was performed using double blind tests on two independent
expert observers as well as automatic segmentation of the proposed method as
compared to conventional velocity threshold on simulated data of minimum jerk
movements; simulated minimum jerk movements were chosen to eliminate bias
towards our MACC based method. The simulated data was created with various
durations and amplitudes and artificially added noise. We demonstrate the
advantages of our method and show that the novel onset detection method is
superior.Finally, we demonstrate the ability of this method to disentangle
between feedforward and feedback adaptation during exposure to visoumotor
delay as well as in a case study with children with cerebral palsy.
This research was supported by a grant from the National Institute for
Psychobiology in Israel -
Founded by The Charles E. Smith Family, and a grant from the Ministry of
Science, Culture &
Sport, Israel,
and by the Ministry of Research, France
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