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Abstract:
Abstract: After prolonged viewing of a unidirectional moving
stimulus, subjects perceive a stationary stimulus as moving in the
opposite direction. Psychophysical studies have demonstrated that
this motion aftereffect (MAE) is diminished following attention to
a central visual stimulus (Chaudhuri 1990), while functional
imaging studies indicate that MAE perception is correlated with
activity in area MT+ (Tootell et al. 1995). The present study
brings together these psychophysical and FMRI findings to ask: (1)
Can attention to a central visual stimulus reduce the MAE-related
signal in area MT+? (2) Can attention to non-visual stimuli
influence activity in area MT+? Echo-planar images were acquired at
1.5 Tesla while subjects viewed moving and stationary stimuli in
alternating blocks. We measured the decay time for signals in MT+
following moving stimuli, in four conditions: (A) reversing
inward/outward motion, which induces no MAE, (B) outward-only
motion with no task, which induces the MAE, (C) outward-only motion
with a concurrent visual task requiring central attention, (D)
outward-only motion with a concurrent auditory task. The MR signal
decayed more slowly following outward-only motion (B) than
following reversing motion (A), as observed in earlier studies. We
found that attention to the visual task (C) caused the MAE-related
signal to decay more rapidly than in the no-task condition (B).
Moreover, attention to the auditory task (D) caused a similar
reduction of the MAE-related signal. These data reveal a
physiological correlate of the behavioral findings, and indicate
that motion processing in MT+ is susceptible to modulation by both
visual and auditory attention.
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