A Comparison Between Adults With Conduct Disorder

8/2/2019 A Comparison Between Adults With Conduct Disorder

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The Psychological Record, 2000, 50, 203-219

A COMPARISON BETWEEN ADULTS WITH CONDUCT DISORDERAND NORMAL CONTROLS ON A CONTINUOUS PERFORMANCETEST: DIFFERENCES IN IMPULSIVE RESPONSECHARACTERISTICSDONALD M. DOUGHERTY, JAMES M. BJORK, DAWN M. MARSH,and F. GERARD MOELLERUniversity of Texas - Houston Health Science Center

Continuous Performance Test (CPT) responding wascompared between 15 adults with a history (childhood/adolescent)of Conduct Disorder (CD) and 15 normal controls. Of particularinterest was whether response latencies and commission errors,which have been suggested to be measures of impulsivity, woulddiffer between the groups. The CPT procedure used included twoconditions: Immediate Memory Task and Delayed Memory Task(IMT/DMT; Dougherty et aI., 1998). Both the IMT (0.5-s delay) andDMT (3.5-s delay with distracter stimuli at 0.5-s intervals) requiredthe subject to respond if a briefly displayed number was identicalto the one presented before it. Stimuli included target (identicalmatch), catch (four of five digits matched), and novel (no match).Participants completed six 22-min testing sessions scheduledacross a single day.The most significant findings were that the CDgroup (compared to the control group) had (a) elevatedcommission errors (responses to catch stimuli); (b) lower stimulusdiscriminability (between target and catch stimuli); and (c) shorterresponse latencies. These results are consistent with the fewprevious studies indicating that these parameters are related toimpulsive behaviors.

A number of different approaches have been used to study impulsiveresponding in the laboratory. One of the most popular methods is theoperant model, which defines impulsive responding as a choice for asmaller immediate reinforcer over a larger delayed reinforcer. Theadvantages of this approach are its rich history from which comparisonscan be made and the clearly defined responses that are amenable tostatistical and theoretical analyses (see Anslie, 1975, for a review). As aresult, the operant conditioning perspective remains a popular model forinvestigating impulsive choice behavior in both humans and nonhumans(e.g., Green & Rachlin, 1996; Rachlin, Raineri, & Cross, 1991). It is importantThis research was supported by grants from the National Institute on Alcoholism andAlcohol Abuse (AA-10095 & AA-10828) and the National Institute on Drug Abuse (DA-08425). Requests for reprints or the computerized memory tasks used in this study shouldbe directed to Donald M. Dougherty, Department of Psychiatry & Behavioral Sciences, 1300Moursund Street, Houston, TX 77030. (E-mail: [email protected]).


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204 DOUGHERTY ET AL.

to recognize, however, that impulsivity measured by operant methodologymay be only one type of impulsive behavior. Impulsivity is multidimensional,in that it involves several aspects of behavior. For example, Barratt andcolleagues (Barratt, 1985; Patton, Stanford, & Barratt, 1995) have proposeda three-factor model of impulsivity. Their theory views impulsiveness as acombination of three distinct factors: (a) motor impulsiveness, which is actingon the spur of the moment and having an inconsistent lifestyle; (b) attentionalimpulsiveness, which is an inability to focus on the task at hand and apropensity for racing and interrupted thoughts; and (c) nonplanningimpulsiveness, which is the inability to plan and think carefully, along with alack of enjoyment of challenging mental tasks. All three factors includedimensions of arousal, information processing, and social learning. Supportfor the three-factor theory has been provided by a factor analyses of theBarratt Impulsiveness Scale-11 (Patton et aI., 1995), a psychometricinstrument of impulsivity.The operant approach to the study of impulsiveness falls primarily intoBarratt's (1985) nonplanning factor of impulsiveness. However, in order tostudy impulsiveness from a different perspective, we used a modifiedversion of the Continuous Performance Test (CPT; Rosvold, Mirsky,Sarason, Bransome, & Beck, 1956), a popular measure of attentionalcapacity. There have been some studies indicating that attentional deficits,as measured by the CPT, may be related to impulsive behaviors (seediscussion below). This approach differs from the operant approach in that ithas characteristics that would seem to involve both the attentional and/ormotor factors of the three-factor theory of impulsiveness.The CPT typically requires participants to respond selectively to aseries of stimuli (e.g., abstract shapes, letters, or numbers) that arepresented briefly and rapidly (usually pre&entations and delays of lessthan 500 ms). Since its inception, the CPT has been modified many times,but usually the subject responds to identify a single target stimulus (e.g.,"0") or a series of target stimuli (e.g., "A" followed by "X") which remainsconstant throughout a testing session. These CPT procedures have beenused to identify and characterize attentional deficits in a variety of subjectpopulations including attention deficit disorder in children and adults(Halperin, Wolf, Greenblatt, & Young, 1991), schizophrenics and personsat-risk for schizophrenia (see reviews by Erlenmeyer-Kimling &Cornblatt,1987; Nuechterlein & Dawson, 1984), as well as persons with learningdisabilities (Dykman, Ackerman, & Oglesby, 1979; Swanson, 1981).Despite the number of variations, the CPT yields several key data,each parameter believed to evaluate different components of attentionalprocessing. Three primary measures are used. First, omission errors (ormisses) are failures to respond to a target stimulus. Most researchersagree that these errors represent deficits in sustained attention orvigilance. Second, commission errors (or false alarms) are responsesmade to stimuli other than target stimuli. Researchers have varied in boththe way they have defined commission errors (in various paradigms) andin the interpretation of these errors. Some have defined commission


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CONDUCT DISORDER AND CPT PERFORMANCE 205

errors as any response to a nontarget stimulus and have suggestedelevated frequency of these errors represents impulsive responding(O'Dougherty, Nuechterlein, & Drew, 1984; Sykes, Douglas, Weis, &Minde, 1971). However, others disagree with the breadth of thisinterpretation (Halperin et aI., 1988, 1991; Sostek, Buchsbaum, &Rapoport, 1980; Sykes, Douglas, & Morgenstern, 1973; Wohlberg &Kornetsky, 1973) and define impulsive-type commission errors as asubset of all errors in which incomplete processing of a stimulus similarto the target leads to a rapid, but incorrect response. These more narrowlydefined commission errors may be more indicative of impulsive behavior.And third, latencies are the delay between the onset of a stimulus and theparticipant's response. Latencies provide information about the temporalrequirements for processing, indicate how difficult a discrimination is in aparticular CPT task, and may also give an indication about how differentpopulations process stimuli before responding (Dougherty et aI., 1998;Halperin et aI., 1988, 1991).The present study was primari'ly concerned with two of the abovemeasures, commission errors and response latencies, because they maybe related to impulsivity. Although some authors may disagree with thisinterpretation, at least part of the skepticism surrounding thisinterpretation stems from the fact that little effort has been made toexternally validate these measures with populations having impulsecontrol problems. The use of commission errors and latencies asmeasures of impulsivity are consistent with the "fast-guess" model ofimpulsivity, whereby judgment or accuracy is found to be compromised forthe sake of speed (Oilman, 1966; Vellot, 1971). According to this model,making decisions takes a certain amount of processing time anddecisions (or responses) made before processing has been completedare impulsive (Sergeant & Sholten, 1985; Sperling, 1984; Vellot, 1971). Inother words, commission errors result from failure to withhold responsesuntil a stimulus identity could be completely processed, and are thereforeimpulsive. When this model is applied to the commission errors andresponse latencies of the CPT, it follows that impulsive responding wouldbe characterized by shorter latencies and more commission errors(because stimuli have not been completely processed).

CPT research with adults with histories of conduct disorder has beenscant. However, other data exist which suggest that men with conductdisorder histories may represent a population likely to evidence CPTperformance deficits. Behavioral disinhibition has been extensivelyresearched in the context of EEG responses evoked during go/no-go tasks.Like the CPT, these tasks require subjects to respond to a target stimulusand to withhold responses to an inhibitory stimulus. In particular, in humansthe neural processes involved in withholding responses to rapidly presentednontarget stimuli generated a substantial P300 EEG wave compared tobrain activity when processing a target stimulus (discussed in Roberts, Rau,Lutzenberger, & Birbaumer, 1994). Interestingly, men with a history ofchildhood conduct disorder (CD) have been shown to have blunted frontal


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cortex electroencephalographic (P300) activity to nontarget stimuli (Bauer,1997). Moreover, in these men, the number of conduct disorder symptomsprior to age 15 correlated negatively with frontal P300 amplitude during atask similar to the CPT used in the present study. Additionally, P300amplitude has been shown to be inversely proportional to BarrattImpulsiveness Scale scores (Barratt, 1965; Branchey, Buydens-Branchey, &Horvath, 1993). This literature suggests that persons with histories of DSMIII-R-defined conduct disorder represent an ideal population in which todetermine the external validity of CPT commission errors and latency asmeasuring impulsiveness.Some studies have found increased commission error rates and shorterlatencies in other impulsive populations. For example, Halperin et al. (1991)found certain types of commission errors on the CPT ("A followed by X"version) to be more frequently made by children with attention deficitdisorder (compared to normal controls), and that reaction times (latencies)were shorter in duration. Commission error rates are also elevated innonalcoholic subjects having a family (parental) history of alcohol-relatedproblems (Miner, 1984; unpublished dissertation) or history of OWl arrests(Koch & Morguet, 1985). These studies indirectly support the idea thatcommission error rates and latencies are perhaps related to impulsive ordisinhibited behaviors/traits.To investigate this possibility, we used a recentlydeveloped CPT procedure (The Immediate Memory Task and DelayedMemory Task, IMT/DMT; Dougherty et aI., 1998).Specifically, the main purpose of this study was to compare CPTperformance between 15 controls and 15 adults with a self-reportedchildhood/adolescent history of behavior that would have met criteria forconduct disorder (CD). We chose CD individuals because impulsivenesshas been an important factor in explaining this common childhoodcondition (Loeber, 1990; Quay, 1988; Schachar, Tannock, & Logan, 1993).Gorenstein and Newman (1980) included CD in a constellation of"syndromes of disinhibition" which they proposed to have a commonfoundation of disinhibited, impulsive behaviors. Because externalizeddisinhibition is a main feature of CD (Windle & Windle, 1993), wehypothesized that adults with a history of childhood CD would havemaintained several impulsive traits, and that these would be evidenced inthe IMT/DMT performance in the following ways: (1) higher rates of falsealarm commission errors, (2) shorter response latencies, (3) lowerstimulus discriminability, and (4) liberal responding strategy (measured bythe signal detection parameter Beta). Furthermore, we hypothesized thatthese measures would be related to scores on a self-reported measure ofimpulsivity, the Barratt Impulsivity Scale (BIS-11; Patton et aI., 1995).

MethodSubjectsThe conduct disorder group (n = 15) consisted of persons who metcriteria for childhood/adolescent conduct disorder (CD) with onset before


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age 15. Diagnosis was made using the Antisocial Personality Disorder(ASPD) modute of the Structured Clinical Interview for DSM-III-R Axis IIDisorders (SCID-II; Spitzer, Williams, Gibbon, & First, 1990; at the time of thestudy the SCID-II fo r DSM-IV was not yet available). In the CD group, 2subjects were Caucasian, 1 was Hispanic, and 12 were African-American.The mean age and years of education for this group were 30.5 + SO 7.4, and11.0 + SO 1.36, respectively. Subjects in the control group (n =15) wererecruited to demographically resemble the CD group with respect to age,education, and race, with the highest matching priorities placed on age andeducation. In the control group, 6 were Caucasian, 3 were Hispanic, and 6were African-American. The mean age and years of education for this groupwere 27.6 + SO 6.4 and 13.6 + SO 1.9, respectively.Both groups were recruited from the community using newspaperadvertisements. Prospective participants were screened in a brieftelephone interview and callers who reported no psychiatric history wereinvited to a subsequent on-site interview. The on-site interview consistedof a medical history interview and a Structured Clinical Interview for DSMIV Axis I disorders (First, Spitzer, Gibbon, & Williams, 1996), as well asthe SCID-II for DSM-III-R (Spitzer, Williams, Gibbon, & First, 1990).Applicants were not admitted for study if the interviews indicated asignificant current medical condition or the presence of current or pastAxis I disorder other than substance abuse.

For both study groups, participation in the research study was voluntaryand informed consent was obtained. All methods and consent forms wereapproved by the University of Texas-Houston Institutional Review Board.Subjects were told that the study was concerned with memory and motorperformance; no mention was made of impulsivity, either verbally or in theconsent forms. After completing the last testing session and otherpsychometric measures subjects were paid approximately $45.Testing schedule. Each subject participated throughout 1 day.Subjects began testing at 0800 hrs, at which time they submitted breathand urine samples for tests of current alcohol or other drug use; allsubject samples tested negative. Subjects then completed a total of sixCPT sessions (using the Immediate Memory Task I Delayed MemoryTask, described below), with each of these sessions beginning at 0830,0930, 1030, 1130, 0130, and 0330. Lunch was provided at noon.Physical apparatus. Behavioral testing was performed in 1.8-m x 1.8-m sound-insulated chamber equipped with an IBM-compatible colormonitor, a ventilation fan (which provided masking noise), and a twobutton computer mouse. A computer located in an adjacent roomcontrolled and monitored experimental events.Continuous Performance TestA modification of the original CPT, the Immediate Memory Task IDelayed Memory Task (IMT/DMT; Dougherty et aI., 1998) was used forthis investigation. In each testing session, the two task conditions (IMTand DMT) alternated in 5-min testing blocks with a 30-s rest period


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preceding each block. The IMT was always first and alternated with theDMT, with each presented twice. As a result, testing sessions lastedexactly 22 minutes. Both conditions are described below.Immediate Memory Task (IMT). This task was designed to measure briefattentional capacity. A series of 5-digit numbers (e.g., 73021) were displayedon the monitor for 0.5 s and separated by a 0.5-s blackout period. Each ofthe digits measured 2.0 cm wide x 3.3 cm high, and the numbers werepresented on the computer monitor in black on a white background.There were several distinct types of stimuli presented and types ofresponses that could be made. Subjects were instructed to respond on thecomputer's left mouse button when a 5-digit number (the target stimulus)appeared that was exactly like the preceding stimulus. The probability of atarget stimulus was 33%. A response made while a target stimulus appearedon the monitor, or made before the next stimulus appeared (1.0 s total), wasrecorded as a correct detection (hit). A failure to respond to a target stimuluswas recorded as an omission error (miss). In addition to target stimuli, therewas a 33% probability that a catch stimulus would appear. A catch stimuluswas a number that differed from the preceding number by one of the fivedigits (its position and value was determined randomly). Responses (errors)made to catch stimuli were considered commission errors (false alarms).The remaining stimuli, novel stimuli (numbers), which were not either targetor catch trials were called filler stimuli and responses made to these stimuli

were categorized as "other errors:' [Note: A novel stimulus always followed atarget or catch trial.]Delayed Memory Task (DMT). This task was designed to measure asubject's ability to retain a stimulus and identify it after a longer delay(compared to the IMT above). The primary difference between this task andthe IMT was that all stimuli (including target, catch, and filler) were separatedby the number "12345:' which was repeated three times at the same rate andduration as all other stimuli. For example, one possible sequence involving atarget stimulus would be: 39863, 12345, 12345, 12345, 39863. Subjectswere instructed to ignore the "12345" and only to remember and identifystimuli separated by the series of "12345" numbers. These stimuli, "12345:'were designated as distracter stimuli. Presenting these distracter stimuliallowed us to increase task difficulty, to control for rates of visual stimuluspresentation, and to improve task sensitivity.In addition to the number of responses made to each type of stimulus,response latencies for correct detections and commission errors wererecorded. The time between onset of stimulus presentation and aresponse was recorded in milliseconds.Psychometric InstrumentsBarratt Impulsiveness Scale (BIS). The BIS (Version 11, Patton et al.,1995) is a self-completed, 30-item questionnaire on which participantsrate their frequency of several common impulsive behaviors and traits(e.g., "I do things without thinking" ) or nonimpulsive behaviors/traits(scored in reverse; e.g., "I am self-controlled") on a scale from 1


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("rarely/never") to 4 ("almost always/always"). In order to examine therelationship between impulsivity and CPT performance, severalcorrelations were made between BIS scores and parameters of the CPT.Wisconsin Card Sorting Test (WCST). The WCST (Computer Version-2; Curtiss &Tuttle, 1993; Heaton, Curtiss, Tuttle, & PAR Staff, 1993) is aneuropsychological test that purportedly measures deficits in frontal lobeor "executive functioning." This test involves memory, abstraction, andsensitivity to performance feedback. A subject is instructed to match acard to one of a set of four stimulus cards based on an unknown sortingdimension (color, shape, or number of symbols) which changesperiodically during testing. To determine whether our two groups differed

in WCST performance, we compared percentage of errors, percentage ofperseverative responses (continuing to match by an incorrect sortingprinciple), and number of categories completed.Beck Depression and Anxiety Inventories. As part of our screeningprocedure subjects completed the Beck Depression (BDI; Beck, Rush,Shaw, & Emery, 1979) and the Beck Anxiety Inventories (BAI; Beck,Brown, Epstein, & Steer, 1988). These instruments were only used toquickly identify persons with possible psychiatric problems and tocompare subclinical symptoms between our two groups.The BDI is a commonly used self-report instrument which provides anumerical index of symptomatology associated with depression. On the

BDI, the rater selects from a series of numerically graded statementspertaining to mood, self-worth, suicidal thoughts, and somaticsymptomatology during the previous week. On the BAI, the respondentassigns a rating from 0-3 to the severity of symptoms of anxiety, such asfear of dying, breathing difficulty, and unsteadiness.Data Analysis. Response latencies to target and catch stimuli,percentages of correct detections (responses to target stimuli),percentages of commission errors (responses to similar but not identicalstimuli), discriminability (d'), and Beta Values (description of d' and Betaparameters appears below in results) were analyzed in repeatedmeasures analyses of variance in a 2 x 6 x 2 design, with task type (IMTvs. DMT) and session (1-6) as within-subject factors, and group (CD vs.control) as the between-subject factor. In the latency analysis, stimulustype (target vs. catch) was also included as a within-subject factor. Finally,response latencies, commission errors (false alarms), correct detections,and BIS scores were correlated using Spearman correlation. Otherbetween-group differences in demographic variables and psychometricinstruments were assessed using independent t tests or chi-square tests(where appropriate). In previous studies we have failed to detect a withinsession effect of block (time) on any parameter of IMT and DMTperformance (e.g., Dougherty et aI., 1998). For this reason, data from thetwo blocks within each testing session were averaged. Additionally,because of the near absence of responses to random and/or distracter"12345" stimuli, statistical analysis of rates of these types of errors wasnot appropriate, and brief"descriptive data are presented instead.


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All correllations were conservatively calculated using Spearman'snonparametric tests because of the number of correlations being done.

ResultsIndependent t tests and chi-square tests indicated that the two subjectgroups did not significantly differ (p > .05) in age, gender, or racialcomposition. The control group averaged 2.6 years more education than the

eo group, which was statistically different [28) = 4.28, P < .001]. APearson's chi-square test showed the incidence of past substanceabuse/dependence between the eD (n = 7) and control groups (n = 3) wasnot significantly different (p> .05). Independent t tests showed commissionerror rates and latencies for IMT and OMT conditions did not differ (p> .05)between subjects with or without a history of substance abuse/dependence.BAI and BDI scores indicated no significant between-groupdifferences in subclinical symptoms of anxiety or depression. Additionally,using independent t tests .we found no group differences in any

component of WeST performance (p > .40 for % errors, % perseverativeresponses, and number of categories completed). Psychometricmeasures (WeST, BIS, BOI, and BAI) were not obtained from 2 subjects.Correct detections (hits). Subjects made responses to the majority oftarget stimuli presented in both the IMT and OMT, making a few morecorrect detections on the IMT than on the OMT [main effect of task typeF(1, 28) =7.504, p = 011]. These data appear in Figure 1. The main effectof session showed a slight, but Significant, increase in correct detectionsacross sessions [F(5, 140) =2.632, P = 026]. The main effect of groupwas not significant, indicating that the groups did not differ in the rates ofcorrect detections [F(1, 28) = 0.718, p = .404].

100en 90c0 80-+-'0a> 70-'Q)0 60+-'0 50)L -L -a 40( )+-' 30cQ) 20L -a> 10..

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Immediate Memory Task

___ Conduct Disorder Group_ Control Group

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100908070605040302010

Delayed Memory Task

O ~ - - ~ - - ~ - - ~ ~ - - ~ -1 234 5Session 6

Figure 1. Percentages of correct detections (correct responses to target stimuli) made forthe conduct disorder and control groups in the IMT (left panel) and the DMT (right panel)across six testing sessions (error bars represent the SEM.).


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All higher-order interaction effects were not significant: task type xsubject group [F(1, 28) =0.013, P= .909], session x subject group [F(5,140) =0.70, P= .622], task type x session [F(5, 140) =0.88, P= .496],and task type x session x subject group [F(5, 140) =0.278, P= 924].Commission errors (false alarms). The CD subjects madeapproximately twice as many commission errors (responses made tosimilar but not identical stimuli) than controls in both the IMT and DMT[F(1, 28) = 28.915, P< .0001]. These data appear in Figure 2. The maineffects of task type [F(1, 28) =1.485, P= 233] and session [F(5, 140) =1.066, P= 381] on commission error rates were not significant.All other effects were not significant: task type x subject group [F(1,28) =0.102, P = .752], session x subject group [F(5, 140) =0.820, p =.537], task type x session [F(S, 140) = 1.76S, p = .124], and task type xsession x subject group [F(5,140) = 0.856, p = .512].

o50

t::: 40Wc::o 30.-E 20(Jc::

10Q)a.

1

Immediate Memory Task

- I I - Conduct Disorder Group-e- Control Group

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50

40

30

20

10

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Delayed Memory Task

23456SessionFigure 2. Rates of commission errors (responses to "catch" stimuli which differed from theprevious stimulus by only one digit). Percentages of catch stimuli to which the conductdisorderand control groups responded in the IMT and the DMT appear in the left and rightpanels, respectively (error bars represent the SEM.).

Discriminability (dJ. The signal detection parameter d', the measure ofdiscriminability between signal and noise (Le., between target and catch stimuli),was calculated and appears in the top panels of Figure 3. For d', higher valuesindicate better discriminability. These values were calculated using standardizedformulas taken from Gescheider (198S, p. 97). The main effect of memory tasktype was significant, indicating that discrimination was more difficult in the DMTcompared to the IMT [F(1, 28) =31.950, p < .0001]. Also, CD subjects had d'values that were significantly lower than controls for both tasks [main effect ofgroup was F(1, 28) =36.418, p < .0001].All other effects and interactions were not significant: session [F(5, 140) =0.S21 , P= 760], session x subject group [F(S, 140) =0.431, P= 83], session xmemory task type [F(5, 140) =0.497, p = 778], subject group x memory task


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type [F(1 ,28) = 1.863, P= .183], and session x memory task type x subject group[F(5, 140) = 0.472, P= .797].Beta. An identical analysis was performed using the signal detectionparameter Beta. These data appear in the bottom panels of Figure 3. Beta scoresgive an indication of how subjects' response criteria are distributed (e.g., eitherconservative or liberal). Higher scores indicate a more conservative responsestrategy. These values were calculated using standardized formulas taken fromGescheider (1985, p. 97). Subjects with histories of CD did not respond moreliberally than controls to CPT stimuli in general. Beta was not Significantly higher incontrols compared to CD subjects [F{1, 28) = 1.059, P = .312]. All subjects weremore conservative in responding to DMT stimuli (higher beta values) than IMTstimuli [memory task type main effect F{1,28) =23.824, P< .0001].

Immediate Memory Task Delayed Memory Task3 3--- Conduct Disorder Group-e-- Control Group2 +-+ +- + + +. 2

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1 1

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o ~ - - ~ - - ~ - - ~ - - ~ - - ~ 1 2 345 6 1 2 345 6Session SessionFigure 3. Shown in this figure are the signal detection parameters d' and Beta.Discriminability (d') between target and catch stimuli in the IMT and DMT are shown for theIMT and DMT in the top panels. Response bias (Beta) values in the IMT and the DMT areshown in the bottom panels (error bars represent the SEM).


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All other effects were not significant: session [F(5,140) = 1.303,. P =.266], session x subject group [F(5,140) = 1.127, P = .349], session xmemory task type [F(5, 140) =0.964, P= 442], subject group x memory tasktype [F(1,28) = 1.31, P = .261], and session x memory task type x subjectgroup [F(5,140) =1.578, P= 170].Response latencies. As shown in Figure 4, response latencies were shorterfor the CD subjects compared to controls across both memory tasks [main effectof group F(1, 28) =4.211 , P= 049]. Across all subjects, latencies were shorterin the IMT than the DMT [main effect of memory task type [F(1 , 28) = 56.893, P< .0001]. The memory task type x group interaction was not significant [F(1, 28)=0.349, P= 559]. In addition, there was also a main effect of session [F(5, 140)=2.651, P= 025], with latencies becoming shorter in succeeding sessions. Thiseffect was not specific to group or to task [session x group F(5, 140) =1.262, P= 283; session x task F(5, 140) =0.813, p= 542].

700.-..

650Ec::.::..600c:Q) 550+- 'ctS...JQ) 500enc:0g.450Q)a: 400 1

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700

- . . - Conduct Disorder- Target 650--+- Conduct Disorder-Catch

23456Session

600550500450

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Delayed Memory Task

23456SessionFigure 4. Response latencies (measured in ms) to target and catch stimuli on the IMT (leftpanel) and the DMT (right panel) .

There was no main effect of stimulus type [target vs. catch; F(1, 28) = 2.582,P= 119] on latency, but the data suggested higher order interactions of stimulusby task type. For example, although response latencies to catch and targetstimuli in the IMT were strikingly similar, there was a trend for longer latencies forcatch stimuli compared to target stimuli in the DMT [stimulus x task type F(1, 28)=3.581, P= 068]. Moreover, the session by stimulus interaction [F(5, 140) =3.171, P = .009] indicated that subjects took longer to respond to catch stimuliacross sessions, and the session x stimulus x memory task type interactionrevealed a trend for this to be specific to the DMT [F(5, 140) =2.181, P= 069].With respect to between-group differences, a significant stimulus x groupinteraction [F(1, 28) = 4.750, P = .037] suggested that CD subjects (but notcontrols) had longer latencies to catch stimuli than target stimuli. No other higherorder interactions were Significant.


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Commission errors corresponded to shorter response times. IMTcommission error rates negatively correlated with mean IMT latencies (r= -.620,p < .0002), as did DMT commission error rates with mean DMT latencies (r =-.740, P< .0001). These Spearman correlations appear in the top panels ofFigure 5. To determ ine whether or not the differences in latencies could beresponsible for the differences in commission error rates between our twogroups, we reanalyzed the between-group differences with latency added as acovariate. In this analysis we found that adjusted mean commission error ratesbetween the two groups were still significantly different in the IMT [group maineffect F(1, 27) =22.044, P= 0001] and DMT [F{1, 27) =24.186, P< .0001].

Immediate Memory Task Delayed Memory TaskC/) 80 80-.6202 -.7403r = r ='- - p = 0002W 70 70 p < .0001c 0 60 60-/)C/) 50 - 50 E E 40 40U .. . .. '+ - 30 300 ... ) 20 20 :.c . E . ::J 10 10Z c 0 0300 400 500 600 700 800 900 300 400 500 600 700 800 900)

Mean Latency (in ms) Mean Latency (in ms)

80 80e r = .4229 r = .1915 .0250 70 .3291= P =c 60 60.-/) I/) 50 50E E 40 400 U 30 30+- '- Q) 20 20 .c E 10 10:JZC 0 0m 40 45 50 55 60 65 70 75 80 85 40 45 50 55 60 65 70 75 80 85) BIS Total Score BIS Total Score

Figure 5. These figures show Spearman's rho correlations between mean response latenciesand mean number of commission errors (top panels) and between the Barratt ImpulsivenessScale (BIS-11) and mean number of commission errors (bottom panels). Ellipses indicate .90normal density using the means, standard deviations, and correlations from the data. The toppanels show a negative correlation between the number of commission errors and latency forboth IMT and DMT. The bottom panels show a positive correlation between the number ofcommission errors and the BIS total score (possible score range: 30-120 points), although thisrelationship was not significant for the DMT condition.


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Other errors. Responding to random (novel) or distracter stimuli ("12345" inthe DMT) was rare in both groups, suggesting that all subjects could easilydiscriminate stimuli which differed noticeably from target stimuli. These errorresponses were made to less than 1 of these stimUli. Collectively, rates ofthese sporadic responses were not suitable for an analysis of variance.Psychometric measures. Barratt Impulsiveness Scale (BIS-11 ; Patton et aI.,1995) total scores were significantly higher for CD subjects (Mean =67.3, SO =7.4) than for controls [M =57.1, SO =13.9; 26) =2.43, P= 0225]. The BISnonplanning subscale scores were also higher for the CD subjects (M=30.9, 'SO =6.9) than for controls [M=23.07, SO =6.6; ~ 2 6 ) =3.081, P= 0048].Neither tt"le motor nor the attentional BIS subscales were significantlydifferent between groups.BIS scores were correlated with IMT/DMT commission error rates(averaged across the six sessions; Figure 5) to determine how impulsivity in theIMT/DMT (conceptua lized here as high commission error rates and shorterlatencies) related to an external measure of impulsivity. Across all subjects, BISscores correlated positive ly with IMT commission error rates (r = .42, P= .025)but not with DMT commission error rates (r = .19, P = .329). Correlationsbetween the BIS and response latencies (target and catch stimuli latencies eachaveraged across sess ions) showed no significant relationship for either the IMT(r= -.19, p= 341) or the DMT (r= .01, P= 926).

DiscussionWe hypothesized that adults whose childhood/adolescent behavior met theStructured Clinical Interview for DSM-III-R (Spitzer et aI., 1990) criteria forConduct Disorder (CD) would perform in a manner consistent with what previousCPT researchers have proposed as impulsive response characteristics.Compared to control subjects, CD subjects had significantly (a) higher rates ofcommission errors (Le., more false alarms) on both the IMT and DMT; (b) shorterresponse latencies (approximately 100 ms); and (c) lower discriminability (d)

between target and catch stimuli.Not only were significant differences observed in IMT/DMT behaviorbetween the two groups, but the BIS total and nonplanning subtrait scores for theCD group were significantly higher than the control group. The BIS total scorealso Significantly correlated with IMT, but not DMT commission error rates, whichis very likely a reflection of fundamental differences in the tasks. The IMT requiresfast, repetitive discriminations and is more closely related to previous CPT tasks,while the DMT is a more difficult task with the inclusion of delays and distracterstimuli. The greater difficulty of the DMT has probably contributed to an increasein variability which reduces the likelihood of finding a meaningful relationship withthe BIS scores. However, overall, the data seem to provide further support for thecontention that CPT commission errors may be related to impulsivity.Our findings are especially interesting given that there exists data indicatingthat electrophysiological responses to commission errors (on tasks similar toIMT/DMT) differ between various populations. For example, men with historiesof conduct disorder prior to age 15 have been shown to have blunted frontal


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cortex electroencephalographic (P300) activity in a task similar to the one usedin our study (Bauer, 1997). The P300 wave is generally considered an indicationof attention or interest. Interestingly, Bauer reported that P300 amplitudedecrements were not evident when subjects were deciding whether to respondto target stimuli, but rather the P300 deficit was evident only when subjects werepresented with stimuli analogous to the CPT catch stimuli of this study. Moreover,these P300 decrements were only found in men with conduct disorder historyprior to age 15. Additionally, P300 amplitude has been shown to be inverselyproportional to Barratt Impulsiveness Scale scores (Barratt, 1965; Branchey etaI., 1993). This neurophysiological data, together with our present findings,suggest that conduct disorder prior to age 15 may predict discrimination andresponse inhibition deficits as an adult.Although the studies described above collectively support the contentionthat commission errors may be an indicator of impulsive behavior, some cautionshould be exercised. Only a handful of studies (mostly with children) haveexamined the relationship between commission errors and impulsivity. Otherinterpretations of the data are plausible. For example, group differences inlatencies and commission error rates may be the result of attentional, memory,or perhaps sensory deficits of adults with a history of conduct disorder. Thesefactors could explain why the CD group showed longer commission errorlatencies compared to the control group. While commission error rates and theoverall CD group latencies were significantly different than controls for both IMTand DMT conditions as we hypothesized, the specific commission error latencygroup difference did not support our hypothesis.Some of the parameters of the IMT/DMT procedures may have maximizeddifferences in commission error rates and are worth noting. First, previousstudies have often used liberal definitions of commission errors, such as definingthese errors as any response made to some stimulus other than the targetstimulus. We suggest that defining commission error responses in this mannerlimits the interpretation of the data. It cannot be determined whether the errorsare made because the subject cannot discriminate between signal (target) andnoise (other stimuli), or whether the errors are a result of a population's elevatedarousal levels (e.g., ADHD Children). Procedures that more conservatively definecommission errors allow for a comparison of two types of error rates betweenstimuli which are both similar to, and different from, the target stimuli. Differentialresponding to these two error types would provide clues to whether responseswere due to discriminability or to higher arousal levels.Second, increasing the task difficulty compared to earlier CPT versionsprovided more distinctive differences between groups. The magnitude of thedifferences in commission error rates between groups was large. Previousstudies which used easier CPT procedures engendered relatively low rates ofcommission errors, and so differences between normal and patient populationswere small. Generally, commission error rates were less than 100;0, withdifferences between populations being less than 5%. Previous researchindicates that detecting subtle differences in attention in adult populationsappears to be dependent on the difficulty of the CPT procedure used; easiertasks are not as sensitive as difficult tasks (for a discussion see Cornblatt & Keilp,


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1994}. Additionally, in order to better discriminate between populations(especially between adult populations) the task should be of sufficient difficulty toproduce sufficient numbers of errors to allow for a better separation betweenpopulations. A higher commission error rate may be more sensitive to theintroduction of independent variable manipulations. .There are a number of obvious routes that future research, examining therelationship between commission errors and impulsivity, should take. First,the effects of drugs of abuse and medications on commission errors shouldbe studied. This can be approached from two different perspectives: (a)studying the effects of medications (e.g., stimulants) on commission errorrates, and (b) how drugs of abuse (e.g., alcohol) may increase commissionerror rates. The expectation, from an impulsivity approach, would be thatalcohol would increase impulsive responding, and stimulants (at therapeuticdoses) would decrease impulsive responding. In fact, a recent study with 18social alcohol drinkers (Dougherty et aI., 1999) found that small doses ofalcohol (achieving BACs of approximately 0.035) increased commission errorrates, and changes in performance were .specific to these errors. Second,commission error rates should be studied by systematically examining theeffects of contingencies on performance to determine whether or notdifferences between populations can be minimized. And third, otherneuropsychological measures should be taken in an attempt to determine thenature of the deficits between populations and to explore whether otherinterpretations of data could account for these observed differences.

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Documents

A Comparison Between Adults With Conduct Disorder