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Abstract:
According to the asynchronous discrete model partial
information can be transmitted from perceptual to motoric
processing stages if stimuli contain more than one separable code,
such as shape and size. This is supported by central motor
activation as indicated by the lateralised readiness potential
(LRP) based on quickly available hand-determining code even when a
second code, available somewhat later, successfully inhibits overt
responding. Because these studies have drawn on stimulus codes
which, according to neurophysiological evidence, are processed in
different visual streams, Experiment 1 assessed partial
transmission for stimulus codes which are both processed in the
dorsal visual stream. In a two-choice Go\NoGo paradigm the code for
the response hand was always defined by the direction of stimulus
movement (dorsal stream). However, Go\NoGo decision was determined
either by movement velocity (dorsal stream) or by stimulus shape
(ventral stream). In both conditions significant NoGo LRPs
indicated partial transmission of the direction information.
Experiment 2 assessed the hypothesis that, if necessary, the visual
system may be flexible enough to transmit partial information even
when there is only one stimulus code. A two-choice Go/Nogo task
with one-dimensional stimuli was employed where hand and Go/Nogo
were determined by easy and hard level-spacings, respectively,
while time-pressure was excerted on RT. On NoGo trials without
muscular activation (EMG) there was nevertheless clear LRP activity
confirming our hypothesis.
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