Association of the Conners’ Kiddie Continuous Performance Test (K-CPT) Performance and Parent-Report Measures of Behavior and Executive Functioning

Abstract

Objective: To explore the relationship between the Conners’ Kiddie Continuous Performance Test (K-CPT) performance and parent-report measures of child behavior and executive functioning, and clarify the role of sex in K-CPT performance in preschoolers. Method: Mothers and children recruited to the Health Outcomes and Measures of the Environment Study with complete 5-year assessment data relevant to the analyses were included (N = 127). We examined the association between K-CPT scores and Behavior Assessment System for Children–Second Edition (BASC-2) and Behavior Rating Inventory of Executive Function (BRIEF) scores, with covariate adjustment. Results: We found no significant associations between K-CPT, BASC-2, and BRIEF scores in the full sample. In sex-stratified analyses, we found unusually fast reaction time on K-CPT was related to executive control difficulties in girls, whereas unusually slow reaction time was related to the same difficulties in boys. Omission errors were associated with executive difficulties only in boys. Conclusion: The K-CPT may prove to be a useful indicator for early onset of executive control difficulties in preschool-aged children.

Keywords

K-CPT BASC-2 BRIEF ADHD attention executive functions continuous performance

ADHD, the most common childhood neurobehavioral disorder (Froehlich et al., 2007), is characterized by clinically significant levels of inattention and hyperactivity/impulsivity (American Psychiatric Association [APA], 2013), as well as multiple areas of functional impairment, including social problems, family dysfunction, and academic difficulties (Mannuzza, Klein, Bessler, Malloy, & LaPadula, 1993). It has been suggested that ADHD arises from a primary deficit in one or several skills that fall under the larger category of executive functions (e.g., response inhibition, working memory, cognitive set-shifting, vigilance/sustained attention, planning/organization; for example, Fuster, 1997; Stuss & Benson, 1986). Meta-analyses of published studies pertaining to ADHD that administered at least one executive functioning measure indicated medium between-group effect sizes (d = 0.53-0.60; Yeates, Ris, Taylor, & Pennington, 2010) for measures of inhibition, working memory, vigilance, and planning in school-age samples (Willcutt et al., 2005; Willcutt, Doyle, Nigg, Faraone, & Pennington, 2005). Given that clinical symptoms of ADHD generally present prior to the age of 12 (APA, 2013), these areas are potential candidates for assessment and early identification of ADHD symptomatology in children. It has been suggested that early detection and intervention in ADHD may prevent or ameliorate the development of the disorder and/or reduce its long-term impact (Sonuga-Barke, Koerting, Smith, McCann, & Thompson, 2011).

Continuous performance tasks (CPTs) are often used to investigate the performance of individuals with inattention, impulsivity, and executive control problems. CPTs generally require participants to inhibit a response to a visually presented stimulus (e.g., a picture or letter). For example, a child may be asked to press a specified key whenever a target stimulus appears and refrain from pressing the key when the non-stimulus appears. CPTs can provide information on participants’ response times, changes in reaction time speed and consistency (i.e., intra-participant variability), commission errors (i.e., hitting a key when the non-target [no go] stimulus is presented), and omission errors (i.e., failing to hit a key when a target [go] stimulus is presented). Omission errors provide a theoretical measure of sustained attention/vigilance, commission errors measure response inhibition, mean hit response time measures speed of processing and responding, and mean hit response time standard error (SE) measures consistency of executive control (Conners, 2001, 2006). CPTs are designed to assess persons of different ages and across different modalities (e.g., Conners, 2014; Diaz-Orueta et al., 2012); however, all CPTs share a common goal of assessing sustained performance over time.

Despite the intuitive mapping of omission and commission errors onto the constructs of vigilance and response inhibition, respectively, the utility of CPTs in detecting ADHD has been called into question due to inconsistent findings across studies. Egeland, Johansen, and Ueland (2009) documented correlations between CPT omission errors and parent and teacher ratings of inattention, and Epstein et al. (2003) found that children with ADHD had more variable CPT response times, increased errors of commission and omission, and poorer perceptual sensitivity compared with control children. In contrast, other studies have not observed significant associations between CPT performance and parent or teacher ratings of inattention or hyperactivity/impulsivity (Alloway et al., 2009).

Sex differences among males and females with ADHD have been documented in several studies. Boys generally exhibit more hyperactivity and impulsivity, and higher rates of comorbid conduct and oppositional defiant disorder; in contrast, girls are more likely to exhibit inattention and experience comorbid anxiety and depressive disorders (e.g., APA, 2000; Gaub & Carlson, 1997; Gershon, 2002; Levy, Hay, Bennet, & McStephen, 2005). A meta-analysis of sex differences in children with ADHD found that females with ADHD were significantly less impaired than males with ADHD, specifically in the areas of hyperactivity (d₊ = .29, p < .05), inattention (d₊ = .23, p < .05), and impulsivity (d₊ = .22, p < .05). In addition, the study found that females with ADHD demonstrated fewer externalizing problems (d₊ = .21, p < .05) and more internalizing problems (d₊ = −.12, p < .05) than males with ADHD (Gershon, 2002).

Intriguingly, however, evidence that boys and girls differ in their CPT performance patterns may help to explain inconsistent associations between CPT performance and ADHD symptoms across studies. Only a few studies have stratified their analyses by sex and evaluated differences in performance on CPTs (for example, Conners’ CPT and various Go/No Go tasks; see Berlin & Bohlin, 2002; Berlin, Bohlin, & Rydell, 2003; Hasson & Fine, 2012; von Stauffenberg & Campbell, 2007). A meta-analytic review studying gender differences among children with ADHD on CPTs (Hasson & Fine, 2012) indicated that boys made more commissions errors when compared with girls (d = .31), with no statistically significant sex difference found with regard to omission errors. Overall, this meta-analysis suggested that inhibitory control performance might be moderated, in part, by sex.

A growing body of research has examined symptoms of ADHD in preschool-aged children using objective measures such as the Kiddie Continuous Performance Test (K-CPT; Conners, 2001, 2006). Several have indicated that preschool children with symptoms of ADHD make more errors of commission and omission on CPT measures when compared with typically developing preschool children (Berwid et al., 2005; Byrne, Bawden, DeWolfe, & Beattie, 1998; Harper & Ottinger, 1992; Mahone, Pillon, Hoffman, Hiemenz, & Denckla, 2005; von Stauffenberg & Campbell, 2007). In addition, on Go/No Go tasks, preschool children exhibiting symptoms of ADHD were found to have more difficulty with inhibitory control as compared with typically developing children (Brocki, Nyberg, Thorell, & Bohlin, 2007; Thorell, 2007). Some studies have examined the relationship between parental ratings of behaviors in preschool children with ADHD and performance-based measures of executive functioning (Berwid et al., 2005; Byrne et al., 1998; Mahone et al., 2005; Thorell, 2007; Youngwirth, Harvey, Gates, Hashim, & Friedman-Weieneth, 2007). Mahone et al. (2005) showed that omission errors on a CPT measure were positively correlated with parent behavior ratings of hyperactivity in preschoolers; however, it is noteworthy that this study utilized a clinical sample. Only a handful of studies have evaluated executive functioning in preschoolers using objective measures of continuous performance in community-based samples (Berlin et al., 2003; Berwid et al., 2005; Thorell, 2007; von Stauffenberg & Campbell, 2007; Youngwirth et al., 2007), and only one (Youngwirth et al., 2007) used the K-CPT in its investigation. This latter study found significant main effects of group (i.e., mother-reported behavioral problems vs. children without behavioral problems) across all K-CPT outcome variables when controlling for the effects of sex, but did not stratify analyses to determine whether the relationship between the K-CPT and behavioral measures differed by sex.

Given that clinical symptoms of ADHD often appear in early childhood, the K-CPT may be a valuable measure for early detection of symptoms associated with ADHD in young children. Thus, the purpose of the current study is to explore the relationship between K-CPT performance and parent-report measures of behavior and executive functioning in preschool-aged children from a community-based, non-clinical sample. In addition, given the sex differences in CPT performance observed in samples of older children, we sought to clarify the role of sex in CPT performance of preschool-aged children and extend the research on sex and CPT performance interactions (Berlin & Bohlin, 2002; Berlin et al., 2003; von Stauffenberg & Campbell, 2007). It is our hypothesis that the relationship between K-CPT performance and parent-reported behavioral outcome measures will differ across males and females, with males exhibiting greater symptoms of hyperactivity/impulsivity in relation to errors of commission when compared with girls.

Method

Participants

The current sample is comprised of mothers and children who were enrolled in the Health Outcomes and Measures of the Environment (HOME) Study. This is an ongoing, prospective pregnancy and birth cohort study designed to examine the impact of low-level exposure to a variety of common environmental toxicants on child health and development. Detailed study eligibility criteria and enrollment methods have been described elsewhere (Yolton et al., 2009). Briefly, between March, 2003 and February, 2006, we enrolled 468 healthy adult (>18 years) pregnant women in the Cincinnati, Ohio area, and 389 remained in the study to deliver live singleton infants. The cohort is socioeconomically diverse, including urban, suburban, and rural participants. Institutional review boards of all involved research institutions, hospitals, and laboratories approved the study protocol. For the current analysis, we included those children who attended the 5-year assessment visit and had complete data relevant to the analysis (n = 127).

Measures

K-CPT

The K-CPT (Version 5; Conners, 2001, 2006), adapted from the Conners’ Continuous Performance Task–Second Edition (CPT-II), was designed for assessment of attention disorders in children 4-to-5 years of age. On the K-CPT, children are presented with a series of easily recognizable pictures (e.g., a house, a soccer ball, and a boat) on a computer screen. The child is required to press the space bar every time he or she sees a picture that is not a soccer ball. The K-CPT run time is set at 7.5 min. Each K-CPT administration includes 5 blocks, each containing a 20-trial subblock of 1.5-s inter-stimulus intervals (ISIs) and a 20-trial subblock of 3-s ISIs (for a total of 200 trials). Stimulus presentation time is 500 ms. The K-CPT was validated on a sample of 454 four- and five-year old children, 314 of whom were classified as non-clinical, while 100 were classified as clinical with ADHD, and 40 were other clinical cases (not ADHD). The K-CPT generates T-scores and percentiles that include (but are not limited to) commission errors (i.e., hitting a key when the non-target [soccer ball] stimulus is presented), omission errors (i.e., failing to hit the key when a target stimulus is presented), hit reaction time, and hit reaction time SE. In addition to these standard performance indicators, Ex-Gaussian indicators of reaction time were also computed using RTSYS 1.0 software (Heathcote, 1996). The Ex-Gaussian indicators represent the sum of the independent Gaussian distribution and the exponential part of the distribution characterized by positive skew. The three reaction time (RT) performance indicators are mu (µ), sigma (σ), and tau (τ). Mu represents the mean, and sigma represents the standard deviation of the normal component of the distribution. Tau represents the exponential component of the distribution or positive skew. High values of tau indicate instances of long RTs in the RT stream. These long RTs characterize one of the primary sources of increased RT variability in children with ADHD (Epstein et al., 2011; Tamm et al., 2012). In the current study, we focused on the T-scores for omissions, commissions, and hit reaction time, as well as tau. For this study, the K-CPT was administered by trained examiners using a standardized script and protocol developed to ensure that all children received identical instructions. This visit was conducted in a quiet room free from distractions in our clinical research center. As the K-CPT was the last test administered within a battery of tests (lasting approximately 90 min), children were offered a short break before beginning the K-CPT.

Behavior Assessment System for Children–Second Edition (BASC-2)

The BASC-2 (ages 2-5; Reynolds & Kamphaus, 2004) Parent Rating Scale was completed by the child’s primary caregiver (typically the mother), in a separate room. This is a 134-item measure validated on a sample of 2,250 preschool-aged children, which offers a comprehensive assessment of a child’s adaptive and problem behaviors in community, home, and school settings. The measure yields composite scores for Adaptive Skills, Behavior Symptoms Index, Externalizing Problems, and Internalizing Problems, as well as clinical subscales for Adaptability, Social Skills, Activities of Daily Living, Functional Communication, Atypicality, Withdrawal, Attention Problems, Anxiety, Depression, Somatization, Hyperactivity, and Aggression. Publisher-supplied software was used to calculate T-scores from entered raw data. To minimize the number of comparisons, the current study focused on the Externalizing Composite and the Attention and Hyperactivity subscales, selected a priori based up relatedness to ADHD symptomatology and previously documented sex differences.

Behavior Rating Inventory of Executive Function (BRIEF)

The BRIEF (Gioia, Isquith, Guy, & Kenworthy, 2000) was also completed by the child’s primary caregiver (typically the mother), in a separate room. It contains 86 items and was validated on a sample of 1,419 children between the ages of 5 and 18. This measure allows parents to rate aspects of a child’s executive functioning, yielding subscale scores for Inhibit, Shift, Emotional Control, Initiate, Working Memory, Plan/Organize, Organization of Materials, and Monitor in the context of his or her everyday environments. The clinical scales form two broad indices (i.e., Behavioral Regulation Index [BRI] and Metacognition Index [MI]) and one composite score (i.e., Global Executive Composite). We included the BRI, MI, and Global Executive Composite (GEC) in the current study.

Covariates

We collected demographic and socioeconomic information (i.e., race, maternal education, marital status, household income, etc.) of the participants in baseline questionnaires. We also completed the HOME Inventory (an observational tool that assesses the quality of the home environment, including physical characteristics, variety of stimulation, and nurturing behavior from the parent; Caldwell & Bradley, 1984) at the 1-year home visit. Child IQ was measured at the 5-year visit using Wechsler Preschool and Primary Scale of Intelligence–III (WPPSI-III) (Wechsler, 2004).

Data Analyses

We examined the data distribution and descriptive statistics of the K-CPT, BASC-2, and BRIEF, as well as mother and child characteristics identified as potential covariates (e.g., maternal age at delivery, socioeconomic factors, substance use/abuse during pregnancy, etc.). In bivariate analyses, we evaluated mother and child characteristics as predictors of K-CPT summary scores. We examined the association between the K-CPT and BASC-2, with adjustment for child sex and covariates that were significant predictors of both K-CPT and BASC-2 summary scores in the bivariate analyses (i.e., child IQ and household income). In addition, we assessed whether the associations differed by child sex in stratified analyses. Similar analyses were conducted to explore the relationship between the K-CPT and BRIEF. All data analyses were conducted using SAS® Version 9.3.

Results

Descriptive Statistics

We included 127 children who completed the K-CPT at age 5 years in the current analysis, of which 125 also had parent-completed BASC-2 and BRIEF assessments. The mothers, on average, were approximately 30 years old at time of delivery, were mostly non-Hispanic White (59%), married (65%), and had at least some college education (76%; Table 1). The median household income was $56,000 (inter-quartile range: $22K-$76K). Forty-two percent of the children were male. The mean child IQ score was 103 (±14). On average, the children completed the K-CPT assessment at age 62 (±3) months. Descriptive statistics of the K-CPT, BASC-2, and BRIEF summary scores are presented in Table 2. The targeted composite/index and subscale T-scores of the these assessments exhibited a mean close to 50 and standard deviation close to 10, indicating this group of children were comparable with the normative population. The 262 children who did not completed the K-CPT (and thus were not included in the current study) had very similar demographic characteristics, such as maternal age (M = 29 [±6] years), race (62% non-Hispanic White), marital status (64% married), and household income (median of $66, 000).

Table 1.

Mother and Child Characteristics (N = 127).

	Value^a
Maternal characteristics
Maternal age at delivery (years)^b	30 (5.7)
Race
White, non-Hispanic	75 (59%)
Black, non-Hispanic	43 (34%)
Other	9 (7%)
Marital status
Married	83 (65%)
Not married, living with someone	14 (11%)
Not married, living alone	30 (24%)
Household income ($)^c	56K (22K-76K)
Employed	112 (88%)
Education
≤HS or GED	30 (24%)
Some college or college graduate	75 (59%)
Graduate or professional school	22 (17%)
Alcohol use during pregnancy
Never drank alcohol during pregnancy	75 (59%)
Drank <1 alcoholic drink per month	38 (30%)
Drank ≥1 alcoholic drink per month	14 (11%)
Marijuana use during pregnancy	5 (4%)
Max. blood lead (microg/dL)^d	0.82 [0.76, 0.87]
Max. serum cotinine (ng/mL)^d	0.092 [0.059, 0.143]
Reported active smoking during pregnancy	13 (10%)
HOME inventory score^b	38 (5)
Children characteristics
Male	53 (42%)
Age at K-CPT exam (months)^b	62 (3)
Full scale IQ (by WPPSI)^b	103(14)

Note. HS = high school; GED = general education development; HOME = to Home Observation for Measurement of the Environment. K-CPT = Kiddie Continuous Performance Test; WPPSI = Wechsler Preschool and Primary Scale of Intelligence.

Numbers present frequency (percent), unless otherwise noted.

Mean (SD).

Median (25th, 75th percentile)

Geometric mean (95% confidence interval).

Table 2.

Descriptive Statistics of the K-CPT, BASC-2, and BRIEF.

	n	Minimum	Maximum	M	SD
K-CPT
Omissions T-score	127	33.4	116.1	54.1	14.7
Commissions T-score	127	35.4	74.3	57.4	8.2
Reaction time T-score	127	18.2	69.2	43.9	10.4
Tau^a	107	67.8	714.6	265.7	120.5
BASC-2
Externalizing T-score	125	31	83	46.7	9.7
Attention T-score	125	33	77	50.5	9.5
Hyperactivity T-score	125	30	82	47.3	9.9
BRIEF
Behavioral regulation T-score	125	33	93	47.0	10.8
Metacognition T-score	125	32	89	45.0	10.1
Global executive T-score	125	32	94	45.7	10.8

Note. K-CPT = Kiddie Continuous Performance Test. BASC-2 = Behavior Assessment System for Children–Second Edition. BRIEF = Behavior Rating Inventory of Executive Function.

Tau, an exponential Gaussian distribution parameter derived for the reaction time, available for 107 children.

K-CPT Outcomes in Relation to Maternal or Child Characteristics

Table 3 presents the K-CPT summary scores in relation to selected mother and child characteristics. The omission T-scores significantly increased with the child’s age, and decreased with higher income and child IQ. The commission T-scores and tau also significantly decreased as child IQ increased. In addition, boys had higher omission errors, lower commission errors, and faster reaction time as compared with girls. Black children also had higher omission errors compared with children of other races/ethnicities. We did not observe significant differences or changes in the K-CPT summary scores in relation to maternal education, marital status, or HOME Inventory scores.

Table 3.

K-CPT Summary Scores by Mother or Child Characteristics.

	Omissions	Commissions	Reaction time	tau
Child sex
Female (ref.)	56.2 ± 8.4	56.8 ± 15.7	46.8 ± 9.9	271.5 ± 126.2
Male	59.1 ± 7.7*	50.2 ± 12.3*	39.7 ± 9.7*	257.3 ± 112.8
Maternal race
Non-Black (ref)	56.4 ± 8.8	53.6 ± 16.1	44.2 ± 10.2	266.8 ± 111.5
Black	59.4 ± 6.5*	55 ± 11.7	43.3 ± 10.8	263.5 ± 139
Maternal education
>High school (ref)	57.8 ± 6.5	57.2 ± 14.9	43.8 ± 11.9	273.6 ± 151.6
HS or less	57.3 ± 8.7	53.1 ± 14.6	43.9 ± 9.9	263.3 ± 110.3
Marital status
Married (ref)	57.1 ± 8.6	52.9 ± 15	43.3 ± 10.2	255.3 ± 112.7
Not married	58 ± 7.5	56.2 ± 14.1	45 ± 10.8	287.1 ± 134.4
Child age (months)^a	0.243**	0.102	0.044	0.131
Household income (K$)^a	−0.203**	−0.106	−0.026	−0.131
Child IQ^a	−0.242**	−0.206**	−0.062	−0.345**
HOME inventory score^a	−0.105	−0.108	−0.05	−0.118

Note. K-CPT = Kiddie Continuous Performance Task. HOME = Home Observation for Measurement of the Environment. Mean and standard deviation reported.

Pearson’s correlation coefficient reported.

comparison with reference group significantly different at p < .05.

p value of coefficient <.05.

Association Between the K-CPT and the BASC-2

In the analyses examining the whole sample, there were no significant associations observed between K-CPT performance and BASC-2 scores, with adjustment for important covariates (i.e., child sex, child IQ, and household income; Table 4). However, analyses stratified by child sex showed a statistically significant association between K-CPT reaction time T-scores and the BASC-2 Externalizing Problems Composite scores (p < .05) in girls, but not boys. Specifically, lower reaction time T-scores (indicating unusually fast reaction time) were associated with more parent-reported externalizing behaviors in girls. No significant associations were noted between K-CPT commission error T-scores or tau and BASC-2 index or subscale scores. Supplemental analyses were run exploring associations between K-CPT reaction time SE, mu, and sigma (see Supplemental Table 1). Reaction time SE was found to be associated with hyperactivity on the BASC-2 in boys only (p < .05); no other significant findings were noted.

Table 4.

Association Between the K-CPT and the BASC-2 (Adjusted for Covariates).

	Omissions		Commissions		Reaction time		tau
	Estimate	p value	Estimate	p value	Estimate	p value	Estimate	p value
Whole sample^a
Externalizing	0.068	.272	0.083	.455	−0.060	.499	0.001	.946
Attention	0.054	.361	0.002	.985	−0.089	.284	−0.009	.268
Hyperactivity	0.101	.113	0.008	.943	−0.035	.698	0.001	.902
Girls only^b
Externalizing	0.061	.423	0.129	.372	−0.245	.034*	−0.004	.663
Attention	0.075	.289	0.094	.481	−0.206	.055	−0.012	.252
Hyperactivity	0.100	.192	0.047	.747	−0.204	.083	−0.004	.734
Boys only^b
Externalizing	0.113	.311	−0.008	.963	0.206	.119	0.008	.458
Attention	0.022	.848	−0.153	.383	0.078	.561	−0.004	.773
Hyperactivity	0.127	.282	−0.072	.699	0.206	.143	0.008	.506

Note. K-CPT = Kiddie Continuous Performance Task. BASC-2 = Behavior Assessment System for Children–Second Edition.

Adjusted for child sex, child IQ, and household income.

Adjusted for child IQ and household income.

p < .05.

Association Between the K-CPT and the BRIEF

With adjustment for important covariates (i.e., child sex, child IQ, and household income), analyses on the whole sample demonstrated no significant associations between K-CPT performance and BRIEF index scores (Table 5). However, in sex-stratified analyses, a strong and consistent relationship between K-CPT reaction time T-scores and all three BRIEF index scores was evident in both girls and boys; and interestingly, the direction of the relationship differed across sex groups. Specifically, lower reaction time T-scores (indicating unusually fast reaction time) in girls were significantly associated (p < .05) with more parent-reported executive difficulties (i.e., elevated BRI, MI, and GEC scores), whereas higher reaction time T-scores (unusually slow reaction time) were associated (p < .05) with more parent-reported executive difficulties (i.e., elevated BRI and GEC scores) in boys. In addition, a statistically significant relationship was noted between increased omission errors and elevated BRI in boys only. No significant relationships were noted among commission errors T-score or tau and BRIEF outcome variables. Supplemental analyses were run exploring associations between K-CPT reaction time SE, mu, and sigma (see Supplemental Table 2). Sigma was found to be associated with the Metacognition and GEC scores (p < .05) on the BRIEF in girls only; no other significant findings were noted.

Table 5.

Association Between the K-CPT and the BRIEF (Adjusted for Covariates).

	Omissions		Commissions		Reaction time		tau
	Estimate	p value	Estimate	p value	Estimate	p value	Estimate	p value
Whole sample^a
Behavioral regulation	0.036	.590	0.040	.738	−0.040	.677	−0.005	.531
Metacognition	0.003	.968	0.038	.735	−0.064	.473	−0.007	.429
Global executive composite	0.019	.776	0.040	.739	−0.055	.561	−0.006	.486
Girls only^b
Behavioral regulation	−0.023	.781	0.196	.208	−0.279	.025*	−0.022	.055
Metacognition	−0.026	.751	0.202	.195	−0.249	.048*	−0.017	.133
Global executive composite	−0.024	.783	0.214	.185	−0.276	.034*	−0.020	.095
Boys only^b
Behavioral regulation	0.238	.040*	−0.233	.206	0.301	.030*	0.022	.071
Metacognition	0.137	.143	−0.248	.089	0.196	.078	0.012	.225
Global executive composite	0.189	.074	−0.265	.109	0.257	.041*	0.017	.124

Note. K-CPT = Kiddie Continuous Performance Task. BRIEF = Behavior Rating Inventory of Executive Function.

Adjusted for child sex, child IQ, and household income.

Adjusted for child IQ and household income.

p < .05.

Discussion

Although ADHD is one of the most prevalent disorders of early childhood, the research community has struggled to find consistent neurocognitive constructs that are predictive of behavioral symptoms associated with the disorder. Different manifestations of symptoms by sex have further complicated clinical characterization and early identification efforts.

The current study sought to investigate the relationship between K-CPT performance and parent-report measures of child behavior and executive functioning in a preschool-aged sample, as well as to clarify the role of sex in K-CPT performance and its behavior-related associations. Adjusted analyses indicated that, across the whole sample, K-CPT performance was not correlated with parent ratings of behavior on the BASC-2 or of executive functions on the BRIEF. Previous research utilizing the K-CPT has focused primarily on clinical samples and/or group comparisons (e.g., children with identified behavioral problems vs. children without behavioral problems). Thus, the current study represents a novel approach in a community-based sample and suggests that, to discern executive control difficulties in preschool-aged children across the population, research may have to focus on empirically supported group differences (e.g., sex differences) in the manifestation of such difficulties.

Despite the lack of whole-sample findings, the current study did find different manifestations of early executive control difficulties, as measured by the K-CPT, across boys and girls. Specifically, the direction of the relationship between K-CPT reaction time and selected behavioral outcome variables (on the BASC-2 and BRIEF) differed by child sex, and omission errors were uniquely associated with parent-reported executive difficulties in boys only.

The Utility of the K-CPT in Early Identification

Psychologists are often asked to identify signs of executive dysfunction in children at increasingly younger ages, both because executive dysfunction (and behavioral manifestations thereof) is commonly seen in children who have experienced a variety of early neurodevelopmental insults (e.g., prematurity, perinatal injury) and because increased awareness of ADHD has resulted in heightened emphasis on early identification. Current results suggest that reaction time (rather than commission errors or tau) may represent a unique indicator of parent-reported symptoms of executive dysfunction in preschool-aged children. Thus, for children who grow up to manifest inattention, impulsivity, and hyperactivity, it is possible that atypically fast or atypically slow reaction time represents an early cognitive indicator of executive control difficulties.

The Importance of Sex

A particularly striking finding of the current study concerns the role of sex in the manifestation of executive control difficulties. Specifically, the direction of the relationship between reaction time and BASC-2 and BRIEF outcome scores was opposite for boys as compared with girls, indicating that atypically fast reaction time was related to elevated BASC-2 and BRIEF scores (and thus greater parent-reported executive dysfunction) in girls, whereas atypically slow reaction time was associated with elevated BRIEF scores in boys. In addition, errors of omission represented a unique predictor of elevated executive difficulties in boys, whereas no such finding was evident in girls. Thus, it is possible that, in girls, unusually heightened vigilance/engagement (e.g., faster reaction time suggestive of hyper-focus) is more predictive of behavioral and attentional difficulties. In contrast, it is possible that, in boys, unusually suppressed vigilance/disengagement (e.g., slower reaction time/omission errors suggestive of lacking focus) is more predictive of such difficulties. Regardless, increased understanding of the initial manifestations of executive control difficulties, and differential manifestation across boys and girls, may enhance early identification and treatment efforts.

Limitations

The current study is not without limitations. First, executive dysfunction in the current sample was measured solely per parent report, and study participants were not assessed for a clinical diagnosis of ADHD. Thus, current results may apply to only a narrow range of executive functioning and, taken in the context of behavioral expectations associated with sex/gender roles, could represent parental reporting bias. As an example, girls who manifest faster reaction time (e.g., hyper-vigilance) may be more readily identifiable as “atypical” to parents, whereas similar behavior in boys might be considered more “normal.” However, as the clinical diagnosis of ADHD and, to a large degree, executive dysfunction more generally, is identified via parent/caregiver/teacher report, this represents a limitation of our clinical diagnostic system as well.

Second, the current study sample included only about one third of the larger HOME study sample. However, the children included are representative of the original HOME study cohort as they are very similar to those who did not complete the K-CPT in terms of baseline demographic characteristics. Third, the current study utilized only one direct measure related to executive control in children (i.e., K-CPT); thus, results may not generalize well to studies using other measures or assessing other aspects of executive functioning. However, few studies in the literature have explored the utility of the K-CPT in characterizing executive functions in young children, and most available studies have explored K-CPT performance in a clinically referred sample. In addition, preschool-aged children were administered a battery of tests, of which the K-CPT was last; thus, fatigue may have factored into performance. Finally, although efforts were taken to carefully select the most empirically supported variables for inclusion in the current analysis to minimize comparisons, no adjustments or controls were made for multiple comparisons in the current study; thus, the generalizability of results should be considered with caution.

Future Directions

The results of the current study, although compelling, are just one step toward better understanding the manifestation of executive control difficulties in early childhood. Future direction for research might include exploration of new variables (e.g., exposure to teratogens either in or ex utero) that may mediate or moderate the relationship between K-CPT performance and parent-reported behavioral outcomes. In addition, future studies may seek to replicate or further characterize the unique relationship between sex and the manifestation of executive control difficulties in preschool children.

In summary, this study is one of the first to explore K-CPT performance as related to ADHD symptomatology and executive control difficulties in a community-based sample. We examined the child-completed K-CPT in relation to parent-completed BASC-2 and BRIEF. Across the whole sample, K-CPT performance was not correlated with behavior on the BASC-2 or executive functions on the BRIEF. However, we found different patterns between boys and girls. In girls, atypically fast reaction time on the K-CPT was related to elevated BASC-2 and BRIEF scores as rated by the parent. In boys, atypically slow reaction time was associated with elevated BRIEF scores in boys, and errors of omission represented a unique predictor of elevated executive difficulties in boys.

Footnotes

Authors’ Note

The Health Outcomes and Measures of the Environment (HOME) Study, on which this research is based, has a formal data-sharing and data-use agreement process. Interested researchers should contact the corresponding author.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was partially supported by grants from the National Institute of Environmental Health Sciences and Environmental Protection Agency (P01 ES11261; R01 ES014575) and the National Institute of Mental Health (K23 MH08388). The study sponsors made no contributions to study design, data collection, analysis, interpretation, authorship, or decisions to submit for publication.

Author Biographies

Holly Barnard, PhD, ABPP/CN, is a board certified neuropsychologist, research associate at Cincinnati Children’s Hospital Medical Center, and active instructor in the doctoral program at the University of Cincinnati. Her research interests primarily include genetic and environment contributors to neurodevelopmental disorders such as ADHD.

Roshni Rao, MEd, is a third-year clinical psychology doctoral student at Wright State University, School of Professional Psychology, and psychology trainee at Cincinnati Children’s Hospital Medical Center. Her research interests include the study of pediatric neurodevelopmental and genetic disorders and effective neuropsychological assessment.

Yingying Xu, MS, is a senior biostatistician at Cincinnati Children’s Hospital Medical Center. She has conducted statistical analyses of various projects involving neurobehavioral outcomes, especially using HOME study data, on which the current study was based.

Tanya Froehlich, MD, is a developmental-behavioral pediatrician and an Associate Professor of Pediatrics at Cincinnati Children’s Hospital Medical Center, where her work focuses on childhood learning and behavioral issues in general and on ADHD in particular. Dr. Froehlich strives for a multi-dimensional understanding of ADHD, and her research has approached the disorder from the vantage points of epidemiology, etiology, and treatment.

Jeffery Epstein, PhD, is a professor of pediatrics in the Division of Behavioral Medicine and Clinical Psychology at Cincinnati Children’s Hospital Medical Center with a joint appointment in the University of Cincinnati, Department of Psychology. He is also the director of the Cincinnati Children’s Center for ADHD. Much of his empirical research has concentrated on ADHD-related cognitive deficits and the promotion of the evidence-based ADHD care in community settings.

Bruce P. Lanphear, MD, MPH, is a clinician scientist at the Child and Family Research Institute, British Columbia Children’s Hospital, and a professor in the Faculty of Health Sciences at Simon Fraser University in Vancouver, British Columbia. He is leading an effort to build an online Atlas of Environmental Health to enhance public understanding of how environmental influences affect human health.

Kimberly Yolton, PhD, is an associate professor of pediatrics at Cincinnati Children’s Hospital Medical Center. She is a developmental psychologist studying the impact of prenatal and postnatal exposures and experiences on subsequent neurobehavioral outcomes in infancy and throughout childhood by way of epidemiologic research methods.

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