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Effects of directional expectations on motion perception and pursuit eye movements

Summary: Effects of directional expectations on
motion perception and pursuit eye movements
Salk Institute for Biological Studies, La Jolla, CA
(Received November 3, 2000; Accepted January 10, 2001)
Expectations about future motions can influence both perceptual judgements and pursuit eye movements. However,
it is not known whether these two effects are due to shared processing, or to separate mechanisms with similar
properties. We have addressed this question by providing subjects with prior information about the likely direction
of motion in an upcoming random-dot motion display and measuring both the perceptual judgements and pursuit
eye movements elicited by the stimulus. We quantified the subjects' responses by computing oculometric curves
from their pursuit eye movements and psychometric curves from their perceptual decisions. Our results show that
directional cues caused similar shifts in both the oculometric and psychometric curves toward the expected motion
direction, with little change in the shapes of the curves. Prior information therefore biased the outcome of both
eye movement and perceptual decisions without systematically changing their thresholds. We also found that eye
movement and perceptual decisions tended to be the same on a trial-by-trial basis, at a higher frequency than would
be expected by chance. Furthermore, the effects of prior information were evident during pursuit initiation, as well
as during pursuit maintenance, indicating that prior information likely influenced the early processing of visual
motion. We conclude that, in our experiments, expectations caused similar effects on both pursuit and perception
by altering the activity of visual motion detectors that are read out by both the oculomotor and perceptual systems.


Source: Adler, Scott A. - Centre for Vision Research & Department of Psychology, York University (Toronto)
Krauzlis, Richard J. - Systems Neurobiology Laboratories, Salk Institute for Biological Studies


Collections: Biology and Medicine