Stroop performance in pathological gamblers

Psychiatry Research 142 (2006) 1 – 10 www.elsevier.com/locate/psychres

Stroop performance in pathological gamblers Semion Kertzman a,b, Katherine Lowengrub a,b, Anat Aizer b, Zeev Ben Nahum a, Moshe Kotler a,b, Pinhas N. Dannon a,b,* a

The Rehovot Community Mental Health and Rehabilitation Clinic affiliated to Beer-Ya’akov-Ness Ziona Medical Complex, Remez Street 80, Rehovot, 76449 Israel b Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel Received 2 June 2005; received in revised form 26 July 2005; accepted 29 July 2005

Abstract Pathological gambling is a relatively prevalent psychiatric disorder that typically leads to severe family, social, legal, and occupational problems and is associated with a high rate of suicide attempts. Understanding the neurobiological basis of pathological gambling is a current focus of research, and emerging data have demonstrated that pathological gamblers may have impaired decision-making because of an inability to inhibit irrelevant information. In this study, we examined pathological gamblers by using the Stroop Color-Word Test, a neurocognitive task used to assess interference control. The breverseQ variant of the Stroop Color-Word Test was administered to a cohort of medication-free pathological gamblers (n = 62) and a cohort of age-matched controls (n = 83). In the reverse variant of the Stroop task, subjects are asked to read the meaning of the word rather than name the ink color. The reverse Stroop task was chosen because it highly discriminates ability to inhibit interference in a population of psychiatric patients. In our study, performance on the reverse Stroop task in the pathological gamblers was significantly slower and less accurate than in the healthy subjects. A new finding in our study was that for pathological gamblers, the average reaction time in the neutral condition (where the color names are displayed in black letters) was slower than the average reaction time in the incongruent condition (where the meaning of the color name and the color of the printed letters are different). This controlled study extends previous findings by showing that performance on the Stroop task is impaired in a sample of medication-free pathological gamblers. D 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Pathological gambling; Decision-making; Stroop task; Cognition; Interference control

1. Introduction

* Corresponding author. The Rehovot Community Mental Health and Rehabilitation Center, Remez Street 80, Rehovot, 76449, Israel. Tel.: +972 8 9461893; fax: +972 8 9468962. E-mail address: [email protected] (P.N. Dannon).

Pathological gambling (PG) is classified in DSMIV (American Psychiatric Association, 1994) as a disorder of impulse control. In the International Classification of Diseases of the World Health Organization (ICD-10), PG is coded under the heading of habit and

0165-1781/$ - see front matter D 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.psychres.2005.07.027

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impulse disorders together with kleptomania, pyromania and trichotillomania. Impulse-control disorders are characterized by an overwhelming urge to perform a harmful act. PG is a chronic, progressive, male-dominated disorder that has a prevalence of 1.0% to 3.4% among U.S. adults (Shaffer et al., 1999). Recently, investigators have postulated that impaired decision-making ability in pathological gamblers may be similar to that seen in patients with lesions of the ventromedial prefrontal cortex (Bechara et al., 1998; Bechara, 2001; Manes et al., 2002). It is of interest that lesions in the ventromedial prefrontal cortex can result in faulty decision-making based on the need for immediate as opposed to delayed gratification (Bechara, 2003). Indeed, recent controlled studies have shown impaired decision-making ability in pathological gamblers. Cavedini et al. (2002) administered the Iowa Gambling Task to pathological gamblers (n = 20) and controls (n = 40). They found that the pathological gamblers had a decreased ability to evaluate future consequences of their actions and had impaired task performance. Brand et al. (2005) extended the results of Cavedini et al. by looking at the performance of pathological gamblers on the Game of Dice Task. In the study of Brand et al., 25 male pathological gamblers were compared with 25 controls, and the frequency of risky decisions was found to be correlated with impaired executive function and impaired feedback processing. The neurocognitive processes involved in decisionmaking are especially relevant in situations where nonrelevant alternatives have been inhibited. bInhibitionQ refers to mechanisms by which the nervous system suppresses information, restricts its use, or restrains its transmission from one area of the brain to another. Inhibition may be defined as a multifactor cognitive process that includes distinct neuropsychological mechanisms (Ridderinkhof et al., 2004). One central inhibitory mechanism is binterference control,Q because the ability to inhibit response to irrelevant information is critical for protecting goal-directed behavior (Barkley, 1997; Kornblum et al., 1999; Nigg, 2000). The Stroop Color-Word Test (Stroop, 1935) is a task for the detection of interference-control impairments that has been widely used in recent psychiatric research (Macleod, 1991; Wright et al., 2003; Bench et al., 1993; Keilp et al., 2005). The Stroop task requires participants to name the ink color of a series of

words that name word colors. In the congruent condition, the color name is the same as the color of the letters; for example, the word bredQ printed in red. In the incongruent condition, the meaning of the printed word and the color of the letters are different; for example, the word bredQ printed in blue, green, or yellow. When subjects are required to report the ink color of the word, greater difficulty is experienced in the incongruent condition. This difficulty can be measured by an increased amount of time required to complete the task (the Stroop interference effect). One explanation for the interference effect is that word reading and the naming of ink colors represent competitive processes. Word reading is an automatic, reflex-like, practiced process. In contrast, color naming is relatively novel and is susceptible to interference from other conflicting processes. Thus, when the two responses are evoked by the same stimulus, the weaker process will require more resources (Botvinick et al., 2001). The measure of inhibition ability is the relative response delay in the Stroop interference condition as measured by response time (RT) in the incongruent condition minus RT in the neutral condition. In a variation of the above paradigm, subjects are asked to name the word rather than to report the ink color, and interference is also observed in the incongruent condition (the reverse Stroop effect). Recent studies have adopted computerized presentation of stimuli, which enables a more precise measurement of RT for Stroop performance (Roe et al., 1980). To date, several small sample studies have assessed interference susceptibility in PG using the Stroop task. Rugle and Melamed (1993) administered the Stroop task to a group of non-substance-dependent, male pathological gamblers (n = 33) and found more impaired performance in PG patients than in controls. Regard et al. (2003) examined a sample of 21 non-substance dependent male pathological gamblers and also found higher rates of impaired Stroop performance compared with performance in healthy controls. As discussed above, Brand et al. (2005) administered the Word Color Interference Test (according to the Stroop paradigm), together with a neuropsychological battery, to a group of male pathological gamblers and found that the frequency of risky decisions in the Game of Dice Task was highly correlated with impairment in specific executive functions, including interference susceptibility. Potenza et al. (2003) studied functional magnetic res-

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onance imaging during Stroop performance in a sample of pathological gamblers. This study yielded contradictory results, for although performance on the Stroop task did not differ significantly between patients and controls, decreased activity in the left ventromedial prefrontal cortex was seen in PG subjects during response to the incongruent condition. It is unclear why Potenza et al., in contrast to other investigators, found no interference effect in the PG patients. They note that the incongruent condition was presented infrequently, and it is possible that differences in the test conditions may account for the differing study results. Furthermore, small sample size represents a significant limitation of the above studies. In our study, we investigated performance on the reverse Stroop effect in a relatively large sample of drug-free pathological gamblers. Our large sample represents an advantage over previous studies. To avoid ambiguous and irrelevant verbal responses, we used a computerized version of the reverse Stroop test with key-press response. We chose the reverse Stroop paradigm because it appears to be more sensitive than the classic or demotionalT Stroop test in detecting interference susceptibility (Sasaki et al., 1993; Durgin, 2000; Atkinson et al., 2003).

South Oaks Gambling Scale (SOGS). Patients with a SOGS score below 5 were excluded. The control group included 83 (25 females and 58 males) healthy volunteers with a mean (F S.D.) age of 40.40 F 10.64 years. The healthy controls did not have a history of impulsecontrol disorders or any other psychiatric axis I or axis II disorders. No significant differences between the pathological gambling subjects and controls were found for age (t = 0.173, P = 0.86), gender (v 2 = 0.076, df = 1, P = 0.78), or education: mean schooling for pathological gamblers was 13.24 F 2.95 years vs. 11.38 F 7.58 years in the controls (t = 1.84, df = 140, P b 0.069). Our study was approved by the local Institutional Review Board, and by the Ministry of Health. All subjects provided written informed consent after the nature of the study was fully explained to them. In the recruitment phase, potential participants completed screening questionnaires and a comprehensive diagnostic interview that covered the following areas: medication history, illicit drug use, family psychiatric history, personal psychiatric history, color blindness, visual and hearing impairment, smoking, literacy, and native language. All of the subjects were free of any psychopharmacologic treatment for at least 4 weeks before the study.

2. Methods

2.1. Stroop measurement

Sixty-two consecutive outpatients (44 males and 20 females) with a diagnosis of pathological gambling were included in our study. The mean (FS.D.) age of the subjects was 40.59 F 13.21 years. All patients were recruited from ambulatory services throughout Israel. Exclusion criteria included the following: (1) comorbid Axis I psychiatric disorders including attention deficit hyperactivity disorder and bipolar disorder, (2) comorbid neurological disorders, (3) mental retardation, (4) alcohol and substance abuse or dependence, and (5) treatment with any psychiatric medication in the month before the screening interview. Note that we defined alcohol and substance abuse/dependence as any use of alcohol or other substances of abuse in the 4 weeks before screening. All patients who were receiving on-going psychiatric care were also excluded from the study. At the screening visit, two senior psychiatrists (PND and KL) administered a semi-structured diagnostic interview, which was performed according to DSM-IV guidelines, and the

We used the breverseQ variant (Abramczyk et al., 1983) of Stroop task (Stroop, 1935), where color interferes with the processing of a color–word combination. The reverse Stroop task was chosen because it highly discriminates ability to inhibit interference in psychiatric patients (Sasaki et al., 1993; Durgin, 2000; Atkinson et al., 2003). For this study, a computerized color-word task was developed (Anima-Scan LTD). The stimuli consisted of four color words (bredQ, byellowQ, bgreenQ, bblueQ). These words were printed in red, yellow, green, blue, or black letters. On each screen appeared the word and two color rectangles at each lower corner of the screen. Subjects were asked to press either of two keys on the keyboard, a left key and a right key, corresponding to the color of the rectangle matching the meaning of the word displayed. The task consisted of 120 items with the same number of neutral, congruent, and incongruent conditions. In the neutral condition (40 items), each of the four color names appeared 10 times displayed in black

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letters. In the congruent condition (40 items), each of the color names appeared 10 times displayed in its corresponding color (i.e., the word bredQ displayed in red letters). In the incongruent condition (40 items), each color name appeared 10 times, and in each of them the word’s meaning did not match the color of its letters (e.g., the word bredQ is displayed in green letters). Individual stimuli were presented in a random order. Assessment of test–retest reliability at 1 month in normal samples yielded the following results: reaction time: neutral 0.95, congruent 0.90, and incongruent 0.86. Accuracy results were as follows: neutral 0.79, congruent 0.77, and incongruent 0.76 (sample of 109 healthy subjects; Kertzman, unpublished data). Stimuli were displayed on the monitor of an IBMcompatible personal computer (Pentium 4) using the experimental software (Anima-Scan LTD), and the Windows 2000 operating system was used. The viewing distance was 60 cm from the screen. Participants were tested for normal color vision before the experiment. 2.2. Procedure All participants completed a familiarization session of the test that included at least 40 practice trials. A feedback system did not permit initiation of the test as long as errors occurred. Following this preparatory procedure, all participants were able to produce accurate key-press responses. In this task, a word and two colored rectangles were displayed. The stimuli were displayed on a gray background and remained on the screen until the participant pressed the key. The color of the letters was always the same as the color of the distracting rectangle. The other rectangle was the appropriate one. The examinee was instructed to ignore the color of the letters of the word, and pay attention only to its meaning. If the meaning of the word was the color of the right rectangle, the examinee was asked to press the right key and vice versa. Participants were instructed to keep their fingers over the key in order to be ready to respond. The testing session began with the following instructions: bRead the color name and match it with the rectangle of the appropriate color. The match should be made according to the meaning of the written color name. A choice of color rectangles will appear on the right or the left side of the screen. Then press the corresponding key as accurately and quickly as possible. Accuracy is

important in this task.Q The test parameters are calculated separately for each of the states (neutral, congruent and incongruent) described above. 2.3. Data analysis Mean reaction time of correct responses and corresponding standard deviation (S.D.) of correct reaction times (RTs) were calculated for each condition (congruent, incongruent and neutral). Errors were defined as the number of incorrect responses and were calculated for each condition. Each participant’s data were first trimmed for outliers according to a standard procedure in which RTs that were 2 S.D. above or below the mean were discarded (Spieler et al., 1996). The interference index was calculated as the difference between the mean RTs of the incongruent condition and the neutral condition. The facilitation index was calculated as the difference between the mean RTs of the neutral condition and the congruent condition. The total interference index was calculated as the difference between the mean RTs of the incongruent and the congruent conditions. 2.4. Statistical analysis Data were analyzed with the Statistical Package for the Social Sciences (SPSS for Windows, version 11.0). Differences between the groups in all test parameters were tested using analysis of variance (ANOVA) for repeated measures. The parameters of the three test conditions served as the within-subject factor, and the group affiliation served as the between-subjects factor. Pearson’s correlation test between parameters was used as appropriate. 3. Results 3.1. Between-group comparison of Stroop performance Table 1 presents the mean results in the PG and control groups. Means in Table 1 are shown in terms of RTs and accuracy, and the composite scores are calculated by dividing accuracy by latency (multiplied by 100). Table 2 depicts mean Stroop effects in both groups. Fig. 1 depicts the time-accuracy trade-off for test conditions for both groups.

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Table 1 Reaction time and accuracy (errors) of performance in the Stroop task among PG patients versus control subjects PG

Control

t

S.D.

Mean

S.D.

1768.57 1388.32 1687.63

943.96 576.26 641.32

891.34 808.57 951.69

264.84 219.83 295.64

8.06** 8.39** 9.23**

1.00 1.00 1.00

Accuracy (correct responses) Neutral 37.29 Congruent 37.42 Incongruent 35.39

5.34 6.02 5.96

39.29 39.53 37.40

2.33 1.78 3.73

3.05** 3.03** 2.49*

0.86 0.85 0.70

0.98 1.08 0.74

4.73 5.21 4.33 83

1.16 1.28 1.37

12.14** 10.65** 10.44**

1.00 1.00 1.00

Reaction time (ms) Neutral Congruent Incongruent

Composite scores Neutral Congruent Incongruent N

2.52 3.07 2.32 62

(df = 143)

Observed power

Mean

*P b 0.05, **P b 0.01.

3.2. Assessment of between-group trial-to-trial changes in Stroop task 3.2.1. Speed of performance PG patients were significantly slower than control subjects [ F(1, 143) = 81.93, P = 0.000]. The interaction between test conditions and group affiliation was also

significant [ F(2, 143) = 13.00, P = 0.000]. Univariate testing of the differences between the groups yielded significant differences in all three conditions: neutral [t(143) = 8.06; P b 0.01], congruent [t(143) = 8.39; P b 0.01], and incongruent [t(143) = 9.23; P b 0.01]; see Table 1 and Fig. 1. However, while the control group was slowest in the incongruent condition, the PG group

Table 2 Stroop indexes among PG patients versus controls—reaction time and accuracy (correct responses) PG

Control

Mean Reaction time (ms) Total interference Interference Facilitation Accuracy (correct responses) Total interference Interference Facilitation Composite scores Total interference Interference Facilitation N *P b 0.05, **P b 0.01.

t

S.D.

Mean

S.D.

299.31 80.94 380.25

336.27 595.27 581.94

143.12 60.35 82.77

124.53 103.56 81.87

2.03 1.90 0.13

1.98 1.76 2.10

2.13 1.89 0.24

0.74 0.19 0.55 62

0.56 0.43 0.53

0.88 0.40 0.48 83

(df = 143)

Observed power

3.89** 2.12* 4.60**

0.97 0.56 1.00

3.46 3.58 0.93

0.20 0.02 0.43

0.06 0.05 0.07

0.47 0.56 0.62

1.61 2.42* 0.71

0.36 0.67 0.11

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posite score in PG patients compared with healthy controls were high on these measures: 1.00 (Table 1).

Accuracy (# of correct responses)

C N

39

3.3. Indices of Stroop performance 38 NC

N

C

37

Group

36 NC

35

Control Gamblers

600

800

1000

1200

1400

1600

1800

Latency (Milliseconds) Fig. 1. Time-accuracy trade-off in pathological gamblers and control subjects: Legends: C—congruent conditions, N—neutral conditions, NC—incongruent conditions of Stroop test.

was slowest in the neutral condition. These results can explain the significance of the interaction described above. Differences between PG patients and controls in the interference control/Stroop effect as measured by RT were 163 versus 61 ms (Table 2). Fig. 1 shows the time-accuracy trade-off. 3.2.2. Accuracy of performance PG patients were significantly less accurate than control subjects in the test [ F(1, 143) = 9.01, P = 0.003]. The interaction between test conditions and group affiliation was not significant [ F(1, 143) = 0.041, P = 0.96]. Univariate testing of the differences between the groups yielded significant differences in all three conditions: neutral [t(143) = 3.05; P b 0.01], congruent [t(143) = 3.03; P b 0.01], and incongruent condition [t(143) = 2.49; P b 0.05]. Testing the composite scores (accuracy by RT / 100), which represent the overall efficacy in the test, yielded the same results: the PG group was less efficient in the test [ F(2, 142) = 131.68, P = 0.000], in all three test conditions: neutral [t(143) = 12.14, P b 0.01], congruent [t(143) = 10.65, P b 0.01], and incongruent [t(143) = 10.44, P b 0.01]. The interaction between the within-subjects factor and the between-subjects factor was significant [ F(2, 142) = 5.84, P = 0.017] due to the difference in RT slowness described above. Effect sizes for Stroop RT and com-

3.3.1. Speed of performance The two groups differed significantly in all three indexes of Stroop performance: total interference, facilitation and interference control indexes (Table 2). The first two effects were stronger in the PG group than in the control group as measured by differences in the total interference index [t(143) = 3.89, P b 0.01] and the facilitation index [t(143) = 4.6, P b 0.01]. The interference effect, on the other hand, was reversed in the PG group: the mean time needed to react to neutral stimuli was longer than the time needed to react to incongruent stimuli [t(143) = 2.12, P b 0.05]. 3.3.2. Accuracy of performance No significant differences in accuracy were found between groups in all three Stroop indexes (Table 2). Testing the composite scores (accuracy by RT / 100), which represent the overall efficacy in the test, revealed that PG patients were less efficient only in the interference control index [t(143) = 2.42, P b 0.05; Table 2]. 3.3.3. Time-accuracy trade-off The number of errors on the Stroop task was differently correlated with RT in both groups. In the control group, the number of errors correlated negatively with RT (r = 0.28, P b 0.05) in the interference condition only, but in the pathological gamblers, an increase in the number of errors that correlated negatively with RT was seen in both the neutral and the

Table 3 Correlations between reaction time and number of errors in Stroop conditions—for PG and control groups Condition

PG

Neutral Congruent Incongruent N *P b 0.05, **P b 0.01.

0.25* 0.09 0.07 62

Control

Confidence interval

0.10 0.20 0.28* 83

2.09** 0.66 2.10**

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congruent, and incongruent) conditions of the Stroop task (Table 4).

incongruent conditions (r = 0.25; P b 0.05; Table 3). There was no significant correlation between the interference control index and education (r = 0.21, P = 0.80).

3.4.2. Time-accuracy trade-off The deviant subgroup of pathological gamblers had significantly lower accuracy and higher latency scores in the neutral and congruent conditions of the Stroop task compared with the bnormativeQ subgroup of pathological gamblers (Table 4).

3.4. Assessment of between-group trial-to-trial changes in Stroop test (deviant performance in PG vs. normative subgroup of PG) 3.4.1. Demographic characteristics The deviant subgroup of PG included 15 men and 10 women with a mean age of 44.28 F 14.06 years versus 38.35 F 12.48 in a second subgroup of PG, which included 27 men and 10 women. No significant between-group differences were found for age [t(60) = 1.74, P = 0.086] or gender [v 2(1) = 1.25, P = 0.536]; for education, the deviant subgroup of PG [mean schooling was 13.52 F 2.7 years vs. normative PG schooling 13.05 F 3.12 years; t(60) = 0.61, P = 0.546]. PG patients with deviant binterference controlQ versus PG patients with normative binterference controlQ were significantly slower only in neutral conditions as measured by RT (Table 4). In addition, a deviant subgroup of PG patients performed significantly less accurately than other PG patients in all three (neutral,

4. Discussion Our study is one of the first controlled studies to measure performance on the Stroop task in a relatively large sample of drug-free pathological gamblers. The results demonstrated that performance on the Stroop task among pathological gamblers was significantly slower and less accurate than performance in the control group. Our results are concordant with previous studies that showed impaired Stroop performance in pathological gamblers (Rugle and Melamed, 1993; Regard et al., 2003). Stroop performance is often used as a measure of impairment in controlled processes (non-congruent conditions) as well as in

Table 4 Reaction time and accuracy (errors) of performance in the Stroop task among PG patients—normal pattern versus deviant pattern Deviant

Normal

t

S.D.

Mean

S.D.

2209.02 1525.03 1704.73

1277.5 746.05 770.50

1470.97 1295.94 1676.07

442.85 412.17 548.44

2.78** 1.40 0.17

0.89

Accuracy (correct responses) Neutral 34.76 Congruent 34.84 Incongruent 32.76

6.91 8.10 7.81

39.00 39.16 37.16

3.01 3.16 3.40

2.89** 2.54** 2.65*

0.90 0.83 0.85

0.86 1.08 0.72

2.90 3.31 2.44 37

0.87 1.02 0.73

4.19** 2.26* 1.55

0.99 0.60

Reaction time (ms) Neutral Congruent Incongruent

Composite scores Neutral Congruent Incongruent N

1.96 2.70 2.15 25

(df = 60)

Observed power

Mean

*P b 0.05, **P b 0.01. Differences between groups: Sex-deviant = 15 men and 10 women; normal = 27 men and 10 women; v 2 (2) = 1.25, P = 0.536. Agedeviant = 44.28 F 14.06, normal = 38.35 F 12.48; t(60) = 1.74, P = 0.086. Education-deviant = 13.52 F 2.7, normal = 13.05 F 3.12; t(60) = 0.61, P = 0.546.

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automatic processes (neutral and congruent conditions) (Tzelgov et al., 1997). Our results demonstrate that pathological gamblers may have more impairment in both automatic and controlled processes than healthy subjects. We note that extensive slowness of processing in Stroop performance may be affected by impairments in reading/processing. In the Stroop study by Regard et al. (2003), a majority of the PG group had dyslexia and signs of developmental disorders. Moreover, poor reading skills may have biased Stroop task results (Savitz and Jansen, 2003). Our results partially support this conclusion, for in our study pathological gamblers who had a deviant Stroop performance were less accurate in all conditions. One of the main findings of our study was that pathological gamblers demonstrated interference control in Stroop performance in a significantly different way from controls. In our sample of pathological gamblers, the average RT for the incongruent condition was, paradoxically, shorter than the average RT for the neutral condition, resulting in a negative interference effect ( 81 ms). This finding of prominent slowness of RT in the neutral condition in our PG sample has not been previously reported (Tables 1 and 2). Our results demonstrate that pathological gamblers appear to have greater difficulty with the least complex level of the Stroop task. Although this result appears to be counter-intuitive, we suggest several possible explanations. Current work in the field of PG has shown that pathological gamblers have faulty cognitive schemata (Toneatto, 1999). The finding of increased RT in the neutral condition among our study subjects may be related to erroneous cognitions and perceptions seen in pathological gamblers. According to Benhsain et al. (2004), gamblers have erroneous beliefs and irrational thinking at the time of gambling. Therefore, extreme slowness of response in the neutral conditions may be related to faulty cognitions such as: bis it possible to have an easy situation?Q or bwhat is the trick/catch in this situation?Q (Joukhador et al., 2004). We hypothesize that faulty cognitions may contribute to poor performance, especially in the subgroup of pathological gamblers who are deviant Stroop performers, for this subgroup has impairment in the speed–accuracy trade-off in two relatively simple conditions (congruent and neutral) versus preserved performance in most complicated conditions (incon-

gruent). We further hypothesize that pathological gamblers may perform better in more challenging situations because they may find a complex task to be more stimulating. Just as pathological gamblers crave the bthrillQ associated with gambling (Milton et al., 2002), so too a complex cognitive task may be perceived as more bexcitingQ than a simple task and so may be associated with improved task performance. The most common method of assessing automatic cognitive biases has been through the bemotionalQ Stroop task (McCusker, 2001), which has better predictive utility for ongoing behavior and for understanding of bloss of controlQ phenomena than selfreport methods of introspection. Researchers using the modified (emotional) Stroop task found that pathological gamblers showed an attentional bias: the pathological gamblers took longer to name the color of the words associated with gambling than they did to name gambling-neutral words (McCusker, 2001). The interference effect in the bemotionalQ Stroop was found only in the participants with low control over their gambling behavior (Boyer and Dickerson, 2003). On the basis of our study results, we propose that the automatized response style seen on the emotional Stroop test when administered to pathological gamblers may be indicative of underlying cognitive deficits such as the inability to inhibit non-relevant responses. In neuroimaging studies, comparison of non-congruent trials (eliciting two conflicting responses) with congruent trials (eliciting only one response) has revealed specific activations in the prefrontal cortex (PFC) (Hazeltine et al., 2003). The PFC contains patterns of neural activity of previously learned stimulus–response associations, and it plays a key role in the decision-making processes underlying response selection (Miller and Cohen, 2001) and related to rule-based action (Bunge et al., 2002; Jiang and Kanwisher, 2003). This finding has been replicated in PG patients who had decreased activity in the ventromedial prefrontal cortex during task performance (Potenza et al., 2003). We also note that Stroop performance is determined by two related mechanisms: goal maintenance and competition resolution. Competence in each domain depends on working-memory capacity (Long and Prat, 2002). Individual differences in working memory capacity appear to predict speed of performance on the Stroop task (Kane and Engle, 2003). Other neural systems that are thought to be crucial to

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interference control include the anterior cingulate cortex and the basal ganglia (Pardo et al., 1990; Larrue et al., 1994; Bush et al., 1998; Peterson et al., 1999; Gruber et al., 2002; Mead et al., 2002). Dysfunction in these cortical areas has also been implicated in impulsive behavior (Visser et al., 1996). The higher number of errors seen in the neutral section of the Stroop task among our PG subjects cannot be explained by a general tendency to impulsivity. If errors are an expression of impulsive performance, a negative correlation should be found between the number of errors and RT. In other words, more frequent bfalse alarmQ reactions may indicate that PG patients are less able to control their reactions and less able to inhibit their motor response when non-target stimuli appear on the screen. Paradoxically, we found this type of error in the neutral condition among pathological gamblers but not in the incongruent condition (Table 3). The primary strengths of our study are the controlled design and the relatively large sample size composed of unmedicated subjects. Our results, however, may be influenced by selection bias, for our patients were selected from an ambulatory setting, and patients with comorbid substance and alcohol abuse were excluded from the study. Since PG is commonly comorbid with alcohol and/or other substance abuse, it is possible that the results of our study may not be generalizable to the population of pathological gamblers seen in actual clinical practice. Another limitation of our study is that results of the Stroop paradigm were not correlated with other tests of executive function or personality traits (such as impulsivity). Despite these limitations, however, our study suggests that the Stroop task can be easily administered to a group of pathological gamblers. This study also shows that pathological gamblers may have specific neurocognitive deficits, for our study subjects had slower and less accurate performance than controls in a neurocognitive test of interference control. An intriguing finding of this study was that our study patients had more impaired performance on neurocognitive tasks of the least complexity. We recommend that future studies address the question of whether pathological gamblers show an inverse relationship between task performance and level of difficulty in tests of neurocognitive function. Further studies are needed to confirm our findings, for there is evidence that neurocognitive deficits in patients with PG may represent

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important predisposing and perpetuating risk factors for gambling behavior.

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