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Abstract:
The perceived motion direction of a (target) stimulus moving
ambiguously in either the left or the right can be disambiguated by
a preceding (prime) stimulus that moves unambiguously in one
direction. Such motion priming typically decays to chance level
over a prime-target interval of about 1s. To examine the underlying
neural mechanisms, we recorded event-related potentials (ERPs) in
17 young adults while they judged apparent motion directions of
single or double jumps of sinewave gratings. Motion priming trials
(an unambiguous motion jump followed by an ambiguous counter-phase
motion jump) were mixed with non-priming control trials (two
unambiguous motion jumps in opposite directions). Priming and
non-priming conditions were compared at each of three prime-target
intervals (200, 400, and 1000 ms). Priming decayed over time-the
target was perceived to move in the same direction as the prime on
96%, 80% and 54% of trials at the 200, 400 and 1000 ms intervals,
respectively. The P3 component of the ERP to the target motion jump
peaked earlier for the 200 ms than for the 400, 1000 ms intervals.
Motion priming was also correlated with a positive enhancement of
ERPs from scalp sites overlying visual cortex beginning 100 ms
after the onset of the target motion. The results reveal that
modulation of both early visual cortical and later neural responses
contribute to motion priming.
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