  This article presents results from an experiment in which 44 human subjects
interact with a dynamic system to perform 40 trials of a command-following
task. The reference command is unpredictable and different on each trial, but
all subjects have the same sequence of reference commands for the 40 trials.
The subjects are divided into 4 groups of 11 subjects. One group performs the
command-following task without preview of the reference command, and the other
3 groups are given preview of the reference command for different time lengths
into the future (0.5 s, 1 s, 1.5 s). A subsystem identification algorithm is
used to obtain best-fit models of each subject's control behavior on each
trial. The time- and frequency-domain performance, as well as the identified
models of the control behavior for the 4 groups are examined to investigate the
effects of reference-command preview. The results suggest that preview tends to
improve performance by allowing the subjects to compensate for sensory time
delay and approximate the inverse dynamics in feedforward. However, too much
preview may decrease performance by degrading the ability to use the correct
phase lead in feedforward.
