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Abstract:
Many different forms of the Stroop attention task have been
used throughout the years to measure inhibitory deficits in
patients with schizophrenia. In order to better understand the
discrepant findings reported in the literature we carried out a
series of experiments which investigated specific task parameters
involved in the standard Stroop attention task. The performance of
chronic schizophrenic patients and matched controls was compared on
different versions of the Stroop attention task designed to isolate
different processing components. Group differences in interference
emerged on the standard clinical version of the Stroop, replicating
the literature, but not on other versions with similar inhibitory
requirements. Differences in interference effects between versions
were found among all subjects as a result of grouping wordtype
(incongruent color/word, neutral and congruent color/word) into
blocks of trials. Grouping produced increased interference effects
due to reduced reaction time (Rt) to the neutral stimulus but had
no effect on Rts to the incongruent stimuli. The data suggest that
under some experimental conditions increased interference may be an
artifact of the neutral presentation.
There is an equal amount of Stroop inhibition required in the
clinical version and the single-trial version of the task, yet
patients with schizophrenia have repeatedly shown increased
interference effects compared to matched controls on the clinical,
but not on the single-trial version. The interpretation of
increased interference effects (i.e. neutral vs incongruent trials)
between the two groups on the clinical version remains to be
resolved. With the identification of these parameters, future
research can more precisely examine the underlying processes
associated with cognitive dysfunction in schizophrenia.
As interference is a score calculated as the difference in
reaction time between the incongruent and neutral stimulus,
increased interference effects should emerge when the subject has
more difficulty inhibiting the incongruent stimulus, not a
facilitation of reaction time to the neutral stimulus. Clinicians
and researchers assume they are measuring the ability to inhibit
irrelevant information with the clinical version of the Stroop
task, but my results suggest that they may actually be measuring
other cognitive processes. There is an equal amount of Stroop
inhibition required in the clinical version and the single-trial
version of the task, yet patients with schizophrenia have
repeatedly shown increased interference effects compared to matched
controls on the clinical, but not on the single-trial version. The
interpretation of increased interference effects (i.e. neutral vs
incongruent trials) between the two groups on the clinical version
remains to be resolved. With the identification of these
parameters, future research can more precisely examine the
underlying processes associated with cognitive dysfunction in
schizophrenia.
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