Abstract | ||
---|---|---|
. Delays in the transmission of sensory and motor information prevent errors from being instantaneously available to the central
nervous system (CNS) and can reduce the stability of a closed-loop control strategy. On the other hand, the use of a pure
feedforward control (inverse dynamics) requires a perfect knowledge of the dynamic behavior of the body and of manipulated
objects. Sensory feedback is essential both to accommodate unexpected errors and events and to compensate for uncertainties
about the dynamics of the body. Experimental observations concerning the control of posture, gaze and limbs have shown that
the CNS certainly uses a combination of closed-loop and open-loop control. Feedforward components of movement, such as eye
saccades, occur intermittently and present a stereotyped kinematic profile. In visuo-manual tracking tasks, hand movements
exhibit velocity peaks that occur intermittently. When a delay or a slow dynamics are inserted in the visuo-manual control
loop, intermittent step-and-hold movements appear clearly in the hand trajectory. In this study, we investigated strategies
used by human subjects involved in the control of a particular dynamic system. We found strong evidence for substantial nonlinearities
in the commands produced. The presence of step-and-hold movements seemed to be the major source of nonlinearities in the control
loop. Furthermore, the stereotyped ballistic-like kinematics of these rapid and corrective movements suggests that they were
produced in an open-loop way by the CNS. We analyzed the generation of ballistic movements in the light of sliding control
theory assuming that they occurred when a sliding variable exceeded a constant threshold. In this framework, a sliding variable
is defined as a composite variable (a combination of the instantaneous tracking error and its temporal derivatives) that fulfills
a specific stability criterion. Based on this hypothesis and on the assumption of a constant reaction time, the tracking error
and its derivatives should be correlated at a particular time lag before movement onset. A peak of correlation was found for
a physiologically plausible reaction time, corresponding to a stable composite variable. The direction and amplitude of the
ongoing stereotyped movements seemed also be adjusted in order to minimize this variable. These findings suggest that, during
visually guided movements, human subjects attempt to minimize such a composite variable and not the instantaneous error. This
minimization seems to be obtained by the execution of stereotyped corrective movements. |
Year | DOI | Venue |
---|---|---|
1997 | 10.1007/s004220050398 | Biological Cybernetics |
Keywords | Field | DocType |
control theory,dynamic system,reaction time,inverse dynamics,central nervous system,closed loop control,feedforward control | Stability criterion,Kinematics,Gaze,Control theory,Inverse dynamics,Control system,Trajectory,Mathematics,Tracking error,Feed forward | Journal |
Volume | Issue | ISSN |
77 | 6 | 0340-1200 |
Citations | PageRank | References |
16 | 2.60 | 4 |
Authors | ||
4 |
Name | Order | Citations | PageRank |
---|---|---|---|
S. Hanneton | 1 | 19 | 3.85 |
Alain Berthoz | 2 | 274 | 33.20 |
Jacques Droulez | 3 | 121 | 15.77 |
Jean-jacques E. Slotine | 4 | 2878 | 344.39 |