11.09.2009 - BIRS: Noise, Time Delay and Balance Control

John Milton

    • Inattention appears to "help" balance
    • Mechanical time-scales matter
    • Stick-balancing appears to be tune to the edge of boundary
      • Don't balance it upright, balance slightly off-center
      • Random walk with an optimal search
        • Non-predictive solution (Maybe stochastic?)
      • Continuous control is too expensive
      • Suggest a discontinuous "act-and-wait"
    • Passive control
      • Better off if you wait to cntrol until stability boundary reached
    • Increased activation delay corresponds to better performance
    • Energy vs Co-energy (How do these correspond to all of the stability studies?)

Bob Peterka

    • Observable behavior
      • Kinematics
      • Ground reaction forces
      • EMG response
      • Muscle images
      • ...neural recordings...
    • Experimental and modeling approaches
      • Musculoskeletal dynamics
      • Sensor dynamics
      • Controller
        • Internal models
          • Head vs Trunk (Thomas Mergner)
            • Perception is not perfect
        • Predictors
    • Experiments
      • Used a pseudo-random turning sequence to rotational perturbations
      • Gain and phase of response to rotational perturbations
        • Gain drops off at high frequency
        • Phase leads at low frequency and lags at high frequency
      • Four modes of control
        • Active control
        • Integrative control
        • Fast-acting control
        • Load control
      • Delayed proprioceptive feedback
      • Positive force feedback (force control)
      • Sensory integration feedback (weighted sensory information)
      • Rapid response control (springs and dampers)

Valero-Cuevas

Toro Okihara

    • Stochastic resonance - does the shaking make things better?
      • Perhaps the shaking helps?
    • Non-locality
      • Need to look at components interacting instead of each individual component

Ami Radunskaya

    • Delay differential equations
      • Euler's method can be "exact" as long as the step-size directly divides the delay-length
      • dde23 - look-up in matlab
      • What about initial requirements on Laplace equations?
\dot{x} = \sin ( x(t-\tau) )
m\ddot{x}(t) +b \dot{x}(t) + q \dot{x}(t-\tau) + k x(t)
b^2 = 4 mk
      • is critically stable in standard spring-mass-damper
      • b>q the system is stable in this delayed equation
      • To find boundary of stability put in solutions of the form
        • Characteristic Polynomial
          • Lambda cannot have imaginary solutions with Re>0
          • If lambda is purely imaginary:
z(t) = e^{\lambda t}
\tau = \frac{1}{\omega}\arctan \left( \frac{\omega^2-k}{\omega b} \right)

Lena Ting

    • Postural control
      • prepatory response (immediate / feedforward)
      • short-latency (stretch reflexes) 40 ms
      • long-latency (automatic postural response) 100 ms
      • decision (steps) 200 ms