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Abstract:
We investigated the costs of two executive functions,
task-shifting and antisaccade performance, and measured the effect
of simultaneous performance of both functions. 18 subjects executed
visual saccades and antisaccades in separate single-task blocks and
within the same mixed-task block. In the mixed-task block,
antisaccade and visual saccade trials were ordered randomly (with a
specifying prompt leading target appearance by 2 seconds) and
subdivided into two groups: 'repeated' trials were preceded by the
same type of trial, and 'shifted' trials were preceded by the
opposite type of trial. Error rate data from the repeated and
shifted trials showed, that the costs of task-shifting and
antisaccade performance were equivalent and additive: the cost of
incorporating both operations in a single response (the shifted
antisaccade) was equivalent to the sum of the costs of doing each
in isolation. In contrast, latency costs of antisaccade performance
were at least three times greater then those of task-shifting.
Furthermore, the effect of adding a task-shift to antisaccades
resulted in a paradoxical decrease in antisaccade latency. This
decrease was not due to a latency-accuracy trade-off, but
correlated with other indices of attention and vigilance. It is
appears that a task-shift facilitates antisaccade performance, or
recent antisaccade performance delays the execution of saccades in
subsequent trials.
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