Seminar Details
2009-02-10 (14.00) : Responsibility Assignment in Redundant Systems
At Euler building
Organized by Mathematical Engineering
Speaker :
White, Olivier
Abstract :
Most movements are produced by the combined action of multiple actors or effectors. Such movements are highly
redundant: each effector can substitute for the contribution of others. Recent research suggests that the brain distributes the
work across different effectors such that signal-dependent noise and/or effort are minimized. When an error occurs during
movement, however, another important problem arises: due to the redundancy, it is not clear from which effector the error
originated. Which effector should carry the main responsibility for online error correction? For which effector should the motor
command be updated in the next movement? Optimally, one would solve these questions based on separate principles: the effector
that is better at correcting online errors should perform most of the correction, and the effector that is most likely responsible for the error, should adapt.
We investigated how the brain distributes correction and adaptation across multiple effectors in a series of redundant tasks in which multiple effectors
controlled the position of a single cursor. To probe online corrections and adaptation, the cursor was visually rotated by a random angle on each trial.
We measured how much each effector corrected for the visual error by determining the difference between the initial and the overall movement direction.
Participants showed a strong tendency to correct more with the left hand. We then estimated the learning rates for each of the involved effectors by fitting a
state-space model to the initial movement directions. We found a clear correlation between the distribution of the online correction and the distribution of the adaptation.
Thus, rather employing separate principles, our results clearly show the brain solves the responsibility assignment jointly for correction and adaptation.
In other words, the effector that is found guilty of committing the error corrects more and adapts more.