Address for correspondence: Jason J.S. Barton, Neurology, KS-454, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215. Voice: 617-667-1243; fax: 617-975-5322.
jbarton{at}caregroup.harvard.edu
Ann. N.Y. Acad. Sci. 956: 250-263 (2002).
Executive functions allow us to respond flexibly rather than
stereotypically to the environment. We examined two such functions,
task switching and inhibition in the antisaccade paradigm, in
two studies. One study involved 18 normal subjects; the other,
21 schizophrenic patients and 16 age-matched controls. Subjects
performed blocks of randomly mixed prosaccades and antisaccades.
Repeated trials were preceded by the same type of trial (i.e.,
an antisaccade following an antisaccade), and switched trials
were preceded by a trial of the opposite type. We measured accuracy
rate and latency as indices of processing costs. Whereas schizophrenic
patients had a threefold increase in error rate for antisaccades
compared to normals, the effect of task switching on their accuracy
did not differ from that in normal subjects. Moreover, the accuracy
rate of trials combining antisaccade and task switching was
equivalent to a multiplication of the accuracy rates from trials
in which each was done alone. Schizophrenic latencies were disproportionately
increased for antisaccades, but again they were no different
from normal subjects in the effect of task switching. In both
groups the effect of task switching on antisaccades was a paradoxical
latency reduction. We conclude that the executive dysfunction
in schizophrenia is not generalized but selective, sparing task
switching from exogenous cues, in which the switch is limited
to a stimulus-response remapping. The accuracy data in both
groups support independence of antisaccade and task-switching
functions. The paradoxical task-switching benefit in antisaccadic
latency effects challenges current models of task switching.
It suggests either carryover inhibition by antisaccadic performance
in the prior trial or facilitation of antisaccades by simultaneous
performance of other cognitive operations.
