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Lydia Krabbendam, Owen O’Daly, Lucy A. Morley, Jim van Os, Robin M. Murray, and Sukhwinder S. Shergill
Using the Stroop task to investigate the neural correlates of symptom change in schizophrenia
The British Journal of Psychiatry 2009; 194: 373-374 [Abstract] [Full text] [PDF]
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[Read eLetter] Issues involved in using the Stroop task in schizophrenia
Preeti Parakh   (14 September 2009)

Issues involved in using the Stroop task in schizophrenia 14 September 2009
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Preeti Parakh,
Junior Resident in Psychiatry
Institute of Medical Sciences, Banaras Hindu University, Varanasi, India

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Re: Issues involved in using the Stroop task in schizophrenia

drpreeti9{at}yahoo.co.in Preeti Parakh

The article was interesting but raised some queries in my mind. The Stroop paradigm has been widely used to examine attention and response inhibition in a variety of mental disorders but certain factors may have a bearing on the results obtained.

In this study, the authors included patients with DSM IV schizophrenia but made no mention of the symptom profile of the cases. Did none of the cases have negative symptoms or affective symptoms? Diminished performance on the Stroop test has been documented in depressed patients (1), anxious patients (2) and in schizophrenics with predominantly negative symptoms (3). Moreover, the neuroanatomical areas implicated in this study have also been implicated in depression. The difference in PANSS scores at baseline and at follow-up has been mentioned for total and positive scores, but not for negative symptoms and general psychopathology scores. Could these differences not have confounded the results?

The authors have excluded people with speech and hearing difficulties but make no mention of people with vision problems. Even subtle defects in visual function have been shown to impact performance on the Stroop task (4). Can National Adult Reading Test scores (which showed a significant difference between cases and controls) serve as a substitute for visual function assessment? And if so, were the patients reassessed for the same when they returned for the follow-up?

The time of testing (level of circadian arousal) may also impact the performance on the Stroop task (5). The authors do not mention if they ensured that the patients coming for follow-up were assessed at the same time as at the baseline visit.

Gender differences are known to affect performance on the Stroop task. But the authors did not match the cases and controls for sex.

References:

1. Kalska H, Punamaki R-L, Makinen-Pelli T, Saarinen M. Memory and metamemory function among depressed patients. Appl Neuropsychol 1999; 6: 96-107.

2. Batchelor J, Harvery AG, Bryant RA. Stroop color word test as a measure of attentional deficit following mild head injury. Clin Neuropsychol 1995; 9: 180-6.

3. Lopes-Machado EZ, Crippa JA, Hallak JE, Guimaraes FS, Zuardi AW. Electrodermically nonresponsive schizophrenia patients make more errors in the Stroop Color Word Test, indicating selective attention deficit. Schizophr Bull 2002; 28(3): 459-66.

4. Anstey KJ, Dain S, Andrews S, Drobny J. Visual abilities in older adults explain age-differences in Stroop and fluid intelligence but not face recognition: implications for the vision-cognition connection. Aging Neuropsychol Cogn 2002; 9: 253-65.

5. May CP, Hasher L. Synchrony effects in inhibitory control over thought and action. J Exp Psychol Hum Percept Perfom 1998; 24: 363-79.