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Abstract:
Previous work indicated that people do not use the speed at which a target is perceived
to move to determine where to hit it. Instead, they use the target's changing position
and an expected speed (based on the speed of previous targets). In the present study we
investigate whether people also ignore the target's perceived direction of motion, and
use the target's changing position and an expected movement direction instead. Subjects
hit targets that moved in slightly dierent directions across a screen. Sometimes
the targets disappeared after 150 ms, long before the subjects could reach the screen.
This prevented subjects from using the target's changing position to adjust their movements,
making it possible to evaluate whether subjects were relying on the perceived or
an expected (average) direction to guide their movements. The background also moved
in some trials. This in
uences the target's perceived movement direction while leaving
its perceived position unaected. When the background was stationary, subjects did
not hit disappearing targets fundamentally dierently than the ones that remained visible.
The moving background aected the direction in which subjects started to move
their hand, in accordance with the illusory change in direction of target motion. If the
target remained visible, subjects corrected their initial error, presumably on the basis
of information about the target's changing position. We conclude that in addition to
the target's position, people use the target's perceived direction of motion when hitting
moving targets. Thus the perceived direction of motion is treated dierently than the
perceived speed.
