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Abstract

De Valois and De Valois [1] showed that moving Gabors (cosine gratings windowed by a stationary
2-dimensional Gaussian envelope) are locally misperceived in their direction of motion.
In a pointing task, Yamagishi, Anderson and Ashida [2] reported even stronger visuo-motor
localization error especially when participants had to make a speeded response. Here, we examined
motion-induced bias in the context of an active navigation task, a situation in which
perception and action are tightly coupled. Participants were presented with a birds-eye view of
a vertically moving contour that simulated observer motion along a path. Observers centrally
fixated while the path and a moving Gabor target were presented peripherally. The task was
to follow the path with the moving Gabor, whose position (left/right) and direction(towards
left/right) were varied in separate blocks. Gabor eccentricity was constant relative to fixation,
with observers adjusting their simulated position with a joystick. Deviations from the path
were analyzed as a function of Gabor direction. We found large and consistent misalignment
in the direction of the moving Gabor, indicating that global position/motion judgments during
action can be strongly affected by irrelevant local motion signals.