An expert table tennis player was required to perform attacking forehand drives
under two ball velocity conditions with normal binocular vision. Under the faster
condition he also performed monocularly. Film analysis results suggest that
under binocular conditions two sources of information were used for timing the
initiation of the drive, viz. ball location and time to frontal eye plane (FEP) - the
time period that would elapse between the moment of movement initiation and the
moment the ball would cross the frontal plane through the eyes. Under the
monocular condition, in which localization of the ball is supposed to be more
diffmlt, the subject tended to slow down his movements. Moreover, while under
the binocular conditions the subject was shown to execute a consistent drive,
under the monocular condition he adapted his drive to the very slight variations
in time to FEP. It is tentatively concluded that under normal (binocular)
Conditions the player simply runs off a standard 'motor programme', while under
the more uncertain (monocular) condition 'programme parameters' are
adaptively varied to match the changes in environmental information.