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Abstract:
Abstract: A new theory models the planning of goal-directed
arm movements with a mechanism specifying local facilitation and
global inhibition (Dynamic Field Theory). The theory predicts that
movements to narrowly spaced targets are excitatory, while
movements to widely spaced targets are inhibitory. These
predictions have been supported neurophysiologically, behaviorally,
and electrocortically. Contrary to Hick's Law, the theory predicts
that a target centered between two medially spaced targets will
increase the excitation to all three targets and lead to decreased
reaction time when compared to the two target case. This prediction
was examined in two experiments measuring reaction time, end-point,
trajectory, and movement time. In both experiments, subjects made a
five-cm movement upon the appearance of an arrow specifying
movement direction from a central position towards a target ring.
In experiment 1, arrows in the two and three-choice conditions were
separated by 90° and 45°. Reaction time data (n=31)
indicated no difference between the two conditions. However, 13
subjects showed shorter reaction times in the three-choice
condition. Experiment 2 was divided into two blocks in which the
target spacing was reduced to 40°/20° (Block 1) and then
further reduced to 20°/10° (Block 2) to increase
facilitation. Every subject (n=9) showed shorter reaction times for
the three-choice task in either Block 1 or 2. Overall, reaction
time and movement related results supported a reversal of Hick's
Law.
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