A planar stick balancing task was investigated using stabilometry parameters (SP);
a concept initially developed to assess the stability of human postural sway. Two
subject groups were investigated: 6 subjects (MD) with many days of balancing a 90
cm stick on a linear track and 25 subjects (OD) with only one day of balancing experience.
The underlying mechanical model is a pendulum-cart system. Two control force models
were investigated by means of numerical simulations: (1) delayed state feedback (DSF);
and (2) delay-compensating predictor feedback (PF). Both models require an internal
model and are subject to certainty thresholds with delayed switching. Measured and
simulated time histories were compared quantitatively using a cost function in terms
of some essential SPs for all subjects. Minimization of the cost function showed that
the control strategy of both OD and MD subjects can better be described by DSF. The
control mechanism for the MD subjects was superior in two aspects: (1) they devoted
less energy to controlling the cart’s position; and (2) their perception threshold
for the stick’s angular velocity was found to be smaller. Findings support the concept
that when sufficient sensory information is readily available, a delay-compensating
PF strategy is not necessary.
