Journal ofNeurology, Neurosurgery, and Psychiatry 1997;62:617-621 617 J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.62.6.617 on 1 June 1997. Downloaded from Use of the Stroop phenomenon as a diagnostic tool for malingering Alicia Osimani, Ariel Alon, Andrea Berger, Jacob M Abarbanel Abstract situation in which the question of malingering Aims-To assess a computerised version arises, not only because of the medicolegal of the Stroop test for detection of malin- referral and the lack of objective symptoms, gering of cognitive deficit. but also due to many misconceptions and prej- Methods-Sixty subjects were assessed udices arising from studies in the early 1960s, using this test. Twenty had cognitive when the diagnosis of "compensation neuro- deficits due to brain damage of miscella- sis" became popular, establishing a mechanistic neous aetiologies. Ten were healthy, not criterion "no objective lesion, no brain dam- acquainted with the test, and were asked age". More recent literature has challenged to simulate cognitive impairment. many of these views. Even apparently mild Another 10 simulators were psychology head injury may sometimes cause severe neu- students trained in the use of the test. robehavioural complications.4 5 The con- Twenty healthy subjects served as con- tention that patients become less symptomatic trols. Results were analysed for reaction after a legal claim is settled has also been stud- time, error percentage, and the Stroop ied by several authors and has not found sup- effect. port.5-7 In addition, no relation has been found Results-There was a significant differ- between the neurobehavioural syndrome and ence in reaction time among groups, social or psychological factors. showing a direct relation of age among In summary, many of the previous views control subjects, and also longer reaction tending to ignore the postconcussive syn- time in patients with brain damage than drome have proved false. This does not mean in controls. Controls and patients with that there are not many people who feign cog- brain damage showed a clear Stroop nitive inability to obtain compensation, but effect. Simulators had a significantly pro- the real frequency of malingering is not clear, longed reaction time, increased error ranging from 3% to 50% depending on the percentage, and inverted or absent Stroop studies.8 effect. This alteration of the Stroop effect Several techniques have been proposed to is never present in organic cognitive identify malingerers. The old clinical concept deficits and seems to be a characteristic can also be applied in neuropsychology: symp- http://jnnp.bmj.com/ pattern of feigning, independently of toms must correspond to known syndromes. knowledge ofthe test. Amnestic patients, for instance, never show Conclusion-This technique is recom- impairment for all memory tasks, although lay mended as a valuable tool to detect people tend to think that memory is a unitary feigned cognitive impairment. process and therefore its impairment must result in failure of every mnemonic task. (7 Neurol Neurosurg Psychiatry 1997;62:617-621) Several studies on malingerers are based on this premise.9 10 on September 26, 2021 by guest. Protected copyright. Lack of consistency between the results of Keywords: malingering; Stroop effect; head injury; reaction time examination and the patient's everyday activi- ties is another important clue. Binder8 reports a Department of case of malingering who had a VIQ of 55 and Neurology, Kaplan The diagnostic and statistical manual-IV' PIQ of 59 but was able to give a detailed his- Hospital, Rehovot, Israel defines malingering as "the intentional pro- tory of his problems and drive his car safely A Osimani duction of false or grossly exaggerated physical around the city. Discrepancy among subtests J M Abarbanel or psychological symptoms, motivated by of a battery may also be an important clue.'I Department of external incentives" and notes that it should A battery to discriminate between simulated Behavioural Sciences, be University ofBen "strongly suspected" when there is a and genuine cognitive impairment would be Gurion ofthe Negev, medicolegal referral, a large discrepancy very useful. However, the increasing media Ber Sheva, Israel between subjective and objective findings, a interest on memory and cognitive problems A Osimani lack of cooperation with evaluation or treat- may enable intelligent simulators to fake cog- A Alon ment, or A Berger the antecedent of antisocial personal- nitive impairment and in some cases malinger- Correspondence to: ity disorder. Mild head injuries usually occur ers may be advised by professionals who are Dr Alicia Osimani, in the context of road traffic, military, or occu- well acquainted with these tests. Department of Neurology, Kaplan Hospital, POB 1, pational accidents. Neuropsychology consulta- Some authors have devised tests which are Rehovot, Israel. tion is usually required for medicolegal difficult to feign even when the subject knows Received 12 October 1995 purposes. The discrepancy between subjective the technique, such as the symptom validity and in final revised form 19 December 1996 and objective findings is the rule in mild head test'2 13 and the portland digit recognition test.8 Accepted 30 December 1996 injury,23 which is perhaps the most frequent We report the application of the Stroop test 618 Osimani, Alon, Berger, Abarbanel J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp.62.6.617 on 1 June 1997. Downloaded from as a diagnostic tool for identifying malingerers. NORMAL CONTROLS It has the advantage that it can detect simula- Group I tion of cognitive impairment, even when the Ten healthy subjects, age range from 20 to 38 subject is familiar with the test. (mean 25) years, participated as controls for The Stroop test'4 is based on the finding groups IV, V, and VI. that for normal people, reading a word takes less time than naming the object or colour cor- Group II responding to that word. Basically, the test Ten healthy subjects, age range from 60 to 75 consists of presenting the names of different (mean 67) years, were controls for group III. colours written in coloured ink. Part of the To have a correct matching for age, educa- stimuli are presented in such a way that word tion, and cultural background, patients from and ink colour correspond that is, the word groups III and IV were asked to bring a "red" is written in red (congruent condition = healthy sibling, spouse, or close relative to be CC), and part of the stimuli consist of words tested as a control. written in a different colour that is, the word "red" is written in blue (incongruent condition PATIENTS WITH BRAIN DAMAGE = IC). As a baseline, a third situation (neutral Group III condition = NC) is often included, in which a Ten patients with diagnosis of mild to moder- meaningless string of letters in different ate cognitive impairment due to degenerative colours is presented. Subjects are asked to or vascular disease were recruited at random name the colour and ignore the written word. from a dementia clinic. Their ages ranged In NC, the meaningless string of letters does from 60 to 75 (mean 68) years. not interfere with colour naming. In CC not only is there no conflict between the two Group IV simultaneous stimuli but there is facilitation, Ten patients with closed head injury were so that reaction time is usually shorter than in recruited from a neurosurgery clinic. Their NC. In IC, reaction time is the longest because ages ranged from 17 to 38 (mean 27) years. the automatic reading of the word interferes Time from injury ranged from six to 10 with the naming of the colour and the subject months and they were diagnosed as having must inhibit the automatic response. The mild cognitive deficits. They were aware of number of errors is also higher in IC. The participating in experimental research that had Stroop effect is the difference between reaction no value for any litigation process. time in IC and NC or CC. The Stroop effect Cognitive deficits were diagnosed by a certi- may be measured in terms of reaction time and fied behavioural neurologist, using general in terms of error percentage because this is clinical examination and a battery of neu- usually higher in IC than NC or CC. Previous ropsychology tests. In group IV, the main reports have shown that the inhibition effect deficits were in the sphere of concentration, as (longer reaction time for IC) is relatively large measured by serial 7's test; and memory, as and stable, whereas the facilitatory effect (RT measured by Rey's auditory verbal learning list difference between CC and NC) is small and and Rey's complex figure. In group III, the may not reach significance.'5 deficits were varied depending on aetiology, http://jnnp.bmj.com/ In neuropsychology this technique has been but all patients had scores between 100 and applied in particular to the assessment of 120 using the Mattis dementia rating scale. frontal lobe function and closed head injury.16 2() Depressed patients have been SIMULATORS reported to show an increased Stroop effect.2 Group V Loss of the Stroop effect has never been Ten normal volunteers taken at random from described in patients with brain damage. hospital staff and from relatives of patients in The accidental finding of an inverted Stroop hospital participated as naive simulators. Ages on September 26, 2021 by guest. Protected copyright. effect (longer reaction time in CC than in IC) ranged from 23 to 35 (mean 25) years. They in three patients suspected of malingering were not acquainted with any neuropsychol- from the history and the results of other tests ogy test. led us to the present study. The objectives were: (1) to compare the results of patients Group VI with brain damage, in particular those with Ten psychology undergraduates, age range head injury, with those of healthy controls and from 23 to 33 (mean 25) years participated in simulators; (2) to assess the efficiency of the the experiment.