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Abstract:
When subjects are required to either repeat the task from the
previous trial or switch to the other task, their reaction times
are found to be larger for switch than repeat tasks. This
deg.Bswitch costdeg.(R) has been repeatedly demonstrated in
behavioral studies. We hypothesize that the behavioral switch cost
may result from two component processes, one is preparation, and
the other is interference. The present study used
electroencephalography (EEG) to study the physiological correlates
of these two component processes. EEGs of 12 healthy college
students were recorded with 33 scalp sites. Subjects completed 480
trials. Each trial consists of a cue, a target, and a response. The
target stimulus was either letter-number pairs (e.g., G7,
A5,deg.K), presented in the center of the screen or letter-only and
number-only pairs (e.g., #7, G&, deg.K). In the fixed-order
condition, subjects were required to perform a letter
discrimination task for a series of two stimuli before switching to
a digit discrimination task for the next two stimuli. In the
random-order condition, subjects were required to perform these two
tasks randomly. The results showed that following the cue, there
was a negativity peaking around 100 msec in the fixed-order
conditions. Following the target, there was an early negativity (30
- 70 msec) and a later negativity (300 - 400 msec) for the
interference stimuli. Our data provide neurophysiological evidence
for the two component processes.
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