In the past two decades, there has been an increased interest in the assessment and treatment of preschool children presenting with concerns about attention problems. This article reviews the research and clinical literature involving assessment of attention and related skills in the preschool years. While inattention among preschoolers is common, symptoms alone do not necessarily indicate a disorder, and most often represent a normal variation in typical preschool child development. Thus, accurate identification of “disordered” attention in preschoolers can be challenging, and development of appropriate, norm-referenced tests of attention for preschoolers is also difficult. The current review suggests that comprehensive assessment of attention and related functions in the preschool child should include thorough review of the child’s history, planned observations, and formal psychometric testing. The three primary methods of psychometric assessment that have been used to characterize attentional functioning in preschool children include performance-based tests, structured caregiver interviews, and rating scales (parent, teacher, and clinician). Among performance-based methods for measurement of attention in the preschool years, tests have been developed to assess sustained attention, selective (focused) attention, span of attention (encoding/manipulation), and (top-down) controlled attention—including freedom from distractibility and set shifting. Many of these tests remain experimental in nature, and review of published methods yields relatively few commercially available, nationally normed tests of attention for preschoolers, and an overall dearth of reliability and validity studies on the available measures.
Keywords: ADHD, preschool, childhood, development, executive function, attention, continuous performance test, cancellation test
Attention Problems in Preschoolers
Attention problems are common among preschool children. By the age of 4 years, as many as 40% of children have sufficient problems with attention to be of concern to parents and preschool teachers (Palfrey, Levine, Walker, & Sullivan, 1985). Symptoms of inattention, even those falling short of formal diagnosis of Attention-deficit/Hyperactivity Disorder (ADHD) are observed to be as high as 3 to 15% in community samples and 50% or higher among clinical referrals (Christophersen & Mortweet, 2003). For example, the number of preschoolers described as “always on the go/driven by a motor” is as high as 72.7% (Pavuluri, Luk, & McGee, 1999). Inattention among preschoolers is not always indicative of ADHD, and may represent a variety of alternative or co-existing conditions, including language disorders, hearing loss, low intellectual functioning, or other forms of psychopathology. Most often, though, inattention is a normal variation observed in typical preschool child development, making identification of “disordered” attention more problematic (Mahone, 2005), especially given the tremendous variability in caregiver ratings of attention and endorsed symptoms of ADHD in this age group (Stefanatos & Baron, 2007). In the past two decades, there has been an increased interest in the assessment and treatment of preschool children presenting with attention problems, especially those associated with symptoms of ADHD, i.e., distractibility and hyperactivity (Shelton & Barkley, 1993). It has been asserted that earlier identification and treatment of attention problems may minimize the harmful impact of childhood disorders, and facilitate appropriate diagnosis, or just as importantly, non-diagnosis (Wilens et al., 2002b).
In the preschool years, ADHD is now the most commonly diagnosed form of psychopathology (Armstrong & Nettleton, 2004), and the prevalence estimates appear to be increasing. For example, DeBar and colleagues (DeBar, Lynch, Powell, & Gale, 2003) reported the occurrence of ADHD to be 2% in a sample of 38,664 general pediatric patients under the age of 5 years, while Connor (2000) reported that the incidence might be as high as 59% in child psychiatry clinics. In another sample of 200 children age 6 years and younger referred to an outpatient psychiatric clinic, 86% met diagnostic criteria for ADHD (Wilens et al., 2002a). The preponderance of research findings suggest that preschool children presenting with disrupted attentional skills are at significant risk for social (Rapport, Scanlan, & Denney, 1999), developmental (Newborg, Stock, & Wnek, 1988), and academic difficulties (Stefanatos & Baron, 2007), relative to typically developing children (American Academy of Pediatrics, 2000), including multiple developmental deficits (Yochman, Ornoy, & Parush, 2006) as well as diagnosis of ADHD and/or other psychopathology in the school-age years (Lahey et al., 2004, 2006; Massetti, et al., 2007; McGee, Partridge, Williams, & Silva, 1991; Wilens et al., 2002b). Attention problems in preschool are also associated with poor social adjustment and frequent emergency medical visits during adolescence (Greenhill, Posner, Vaughan, & Kratochvil, 2008). Even sub-threshold ADHD in early childhood has been shown to be associated with later academic failure and grade retention (Bussing, Mason, Bell, Porter, & Garvan, 2010). Preschool children who actually meet formal diagnostic criteria for ADHD are at even higher risk for behavior problems 6 years later (Lahey et al., 2006), as well as depression and suicidal behavior by age 18 (Chronis-Tuscano, et al., 2010). The Centers for Disease Control estimated that between 1998 and 2009, nearly 9% of children in the US (1 in 11 children between the ages of 5 and 17) have ADHD, with boys receiving the diagnosis approximately twice as often as girls (Akinbami, Liu, Pastor, & Reuben, 2011). Nevertheless, the proportion of girls exhibiting attention problems has also increased rapidly over the past two decades. A recent large epidemiological study of 3907 children found that of the 8.7% who met DSM-IV-TR criteria for ADHD, 51% were boys and 49% were girls (Froelich et al., 2007).
While early identification and treatment of attention problems in preschoolers may minimize the adverse impact (Sonuga-Barke, Koerting, Smith, McCann, & Thompson, 2011), prior to age 4 years, it is difficult to characterize the behavioral features specifically associated with ADHD (or other co-existing disorders), and to distinguish them from attentional difficulties that occur in typically developing children (Smidts & Oosterlaan, 2007). Some researchers have noted that preschool children who meet criteria for the Inattentive ADHD subtype are actually more likely to go on to have reading, spelling, and mathematics problems compared with those presenting with primarily hyperactive/impulsive behaviors, who are more likely to go on to develop ADHD (Massetti et al., 2007). Other investigators have questioned whether the Inattentive subtype of ADHD is meaningful at all in the preschool years; Egger and colleagues noted that the Inattentive subtype of ADHD occurs in fewer than 1 in 1000 preschoolers in the general population (Egger, Kondo, & Angold, 2006). Given these considerations, development of valid objective methods for assessing attention in preschool children is particularly important. Since diagnostic thresholds tend to be viewed though the expectations of those applying the standards (i.e., parents, teachers), what is considered a “disorder” can change over time (Sonuga-Barke et al., 2011), and relying on parent or teacher reports of child symptoms in isolation can lead to over-identification of disorders (Gimpel & Kuhn, 2000). Further, when impairment criteria from the Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR; American Psychiatric Association--APA, 2000) are used carefully in diagnosing preschoolers, fewer children actually meet formal diagnostic criteria for ADHD (Healy, Miller, Castelli, Marks, & Halperin, 2008). Additionally, while ADHD is presently treated as a categorical phenomenon for the purposes of DSM-IV-TR, the syndrome more likely represents dimensional variations rather than a categorical entity (Sonuga-Barke et al., 2011), and the DSM-V is likely to reflect these changes (APA, 2012; Stefanatos & Baron, 2007). Thus, psychometrically sound assessment methods can help quantify these dimensions more accurately, and can facilitate diagnostic accuracy in young children.
Risk Factors for Attention Problems in Preschoolers
Early developmental differences involving attentional control in preschoolers are considered to arise from a variety of influences, including genetic (Biederman & Faraone, 2002), temperamental (Nigg, Goldsmith, & Sachek, 2004), and environmental (Pauli-Pott & Becker, 2011) factors. A recent longitudinal study of over 2000 children from Canada, who were followed from age 5 months to 8 years, showed that the strongest early predictors of attention problems included premature birth, low birth weight, prenatal tobacco exposure, non-intact family, young maternal age, paternal history of antisocial behavior, and maternal depression (Galera et al., 2011). Similarly, a recent study conducted in Israel found that several parameters observed during infancy (birth-1 month) were significantly associated with later development of ADHD: advanced maternal age, lower maternal education, family history of ADHD, and family history of social problems. Between 3–18 months, decrease in head circumference, delay in motor and language milestones, and difficult temperament were all significantly associated with later onset of ADHD, suggesting that temperament, family environment, and early developmental delays are significant risk factors in the preschool years (Gurevitz, Geva, Varon, & Leitner, 2012). As part of the Family Life Project, researchers evaluated behavior and associated risk factors for attention problems among preschoolers ages 3–5 years. They observed that symptoms of inattention and hyperactivity occurred along a single latent factor that did not vary over the preschool years. Further, they observed that low caregiver educational level was the single best predictor of symptom severity (Willoughby et al., 2012).
In the past decade, there has also been increasing concern regarding the amount of screen media used by young children and its relationship with early attention problems. Using retrospective data from the National Longitudinal Survey of Youth, researchers found that number of hours of television watched per day at age 1 and 3 years was associated with attention problems at age 7 years (Christakis, Zimmerman, DiGiuseppe, & McCarty, 2004). There may even be immediate cognitive effects of short-term television viewing in young children. In a recently published study, children who watched a fast-paced television show (specifically a popular fantastical cartoon about an animated sponge that lives under the sea), performed more poorly on a Tower of Hanoi test immediately after viewing than those who had not watched the show (Lillard & Peterson, 2011). These associations remain controversial, however, and there is still a question of whether inattention, per se, represents a cause or an effect of increased television viewing. Nevertheless, the American Academy of Pediatrics (AAP) has taken a conservative approach to television viewing by young children, and has recommended no screen time for children under age 2 years and no more than 1–2 hours a day of quality television and media for older children (AAP, 2011).
Neuropsychological Models of Attention
Attention encompasses several important neuropsychological processes that develop rapidly during the preschool years, including the ability to focus on and attend to stimuli over a period of time and the capacity to take in and report back stimuli immediately after presentation (White, Campbell, Echeverria, Knox, & Janulwicz, 2009). Attention can be considered the foundation on which most other cognitive and neuropsychological functions develop (Cooley & Morris, 1990). Multiple models of attention in the adult brain have been articulated; however, fewer have been translated to apply clinically to the assessment of children (Mahone, 2005). When attentional models are applied to younger children, there exists greater overlap with other developing skills, e.g., executive function, language, visuospatial skills (White et al., 2009), and tests designed to measure attention are affected by (and dependent on) skill development in these other neurobehavioral domains. The prominent neuropsychological models of attention, and their relationship to behavior among preschoolers, are outlined below.
As humans, our senses are constantly bombarded by stimuli. Because there are limits to the capacity of human information processing, development of goal-directed behavior requires a high degree of selectivity within the attentional system (Lachter, Forster, & Ruthruff, 2004). To this end, Broadbent (1958) proposed a selective filter model of attention in which stimuli are selected via top-down control to be processed further, while non-selected (filtered) information is not processed beyond the extraction of its basic physical features. This filtering mechanism becomes more efficient over the course of early development as children use a larger proportion of their attentional capacities to focus on relevant tasks or stimuli (Lane & Pearson, 1982). Broadbent’s theory provided the basis for other contemporary attentional theories (described below), especially those involving selective attention. The selective attention system includes two competing processes: bottom-up and top-down. Bottom-up attention occurs when the brain automatically orients or attends to sensory features in the environment that stand out in some way. Conversely, top-down attention involves conscious (effortful) control of attention toward some target (including shifting of attention). Bottom-up attention has long been considered to be dependent on the posterior parietal cortex, whereas top-down attention is considered to be dependent on the prefrontal cortex and its connections. However, more recent evidence from studies in primates suggests that the dorsolateral prefrontal cortex is also involved in visually based bottom-up selective attention (Katsuki & Constantinidis, 2012).
Pribram and McGuinness (1975) proposed a related theory in which arousal, activation, and effort act as essential elements in controlled attention. In their model, arousal is defined by the orienting response to sensory input (bottom-up), and is considered dependent on the brainstem, reticular system, and hypothalamus. As children mature beyond the preschool years toward adolescence, forebrain control over this system (top-down) is exerted by the amygdala and frontal cortex—which regulate arousal (phasic, short term attention), and by the basal ganglia—which regulate activation (tonic, longer lasting attention). Pribram and McGuinness highlighted the importance of automatic and effortful cognitive processes in understanding attentional control. In their model, automatic processing is performed without intention. It is necessarily brief, not limited by short-term memory, and preferentially processed by the left cerebral hemisphere. Conversely, effortful (conscious, top-down, frontally-mediated) processing, which invokes limitations on one’s capacity, is necessarily slower, uses serial processing, and is used for novel information (Goldberg & Costa, 1981).
Posner and Peterson (Peterson & Posner, 2012; Posner & Peterson, 1990) have asserted that attention is not carried out in a single section of the brain, but rather in a network of regions that complete different, complementary functions. This attentional network is considered separate from the systems of the brain that process data. In the Posner and Peterson model, three primary functions of the attention network are sensory orientation, detection and conscious processing of signals, and maintaining a state of alertness. Visual orienting, which is probably the most relevant to performance-based tests of attention in children, is considered a primary function of the posterior parietal cortex, as well as the lateral pulvinar nucleus of the postereolateral thalamus, and the superior colliculus, with each part carrying out a specific function important in disengaging from a previous focus, shifting, and encoding information from the new stimuli. Posner has asserted that when a target is detected, the brain disengages from a general state of alertness, orients in order to process specific information from that target, and prepares to respond to those specific signals. The brain then maintains a more specific pattern of alertness in order to continue processing (or orienting to) signals with a higher priority. This activation appears to occur primarily in the right hemisphere and involves the noradrenergic system, which is considered to increase the rate of selection of high priority visual information.
Selective or focused attention as described in the models above is often measured using paradigms in which an individual is given two or more concurrent stimuli (or dimensions of stimuli) and must attend to one and ignore the others (Cooley & Morris, 1990). Examples of selective attention measures include: perceptual matching tasks, in which individuals are shown pictures or objects and asked to indicate if a picture is same or different than another; central-incidental learning tasks, in which individuals are given stimuli representing two or more categories, with one designated as central (or important), and then asked to recall both central and non-central (incidental) details; and, visual search or cancellation tasks (described below) in which individuals are asked to search a visual display for a predetermined target.
A criticism of the Broadbent (1958) and other theories of selective attention is that they do not adequately account for simultaneous or parallel processing, requiring divided attention (Lachter et al., 2004). Divided attention is required when one is given two concurrent tasks or stimuli and instructed to respond to both components. Tasks requiring divided attention differ from selective attention tasks by virtue of the additional demand for number of items attended to, thus requiring additional top-down control (Cooley & Morris, 1990). A common method for assessing divided attention is the dual-task interference paradigm, in which (for example) performance on a task is carried out alone, and then contrasted with performance on the same task performed at the same time as a competing task. NEPSY Statue (described below) is an example of a divided attention task that can be used in preschoolers.
Sustained attention or vigilance involves the maintenance of attention over time, and is often based on paradigms that require individuals to detect changes in stimuli over longer periods of time, such as continuous performance tests (Cooley & Morris, 1991). In a model based primarily on factor analytic methods applied to neuropsychological measures in adults and children, Mirsky and colleagues (Mirsky, Anthony, Duncan, Ahern, & Kellam, 1991) were among the first to use continuous performance tests to measure sustained attention. In their studies, Mirsky and colleagues suggested that there are at least four distinct attention functions. These four functions included: focus-execute (i.e., target selection and response—similar to selective attention), sustain (i.e., vigilance, persistence), shift (i.e., flexibility of attentional focus), and encode (i.e., registration, mental manipulation, and recall of information). Similar factors were observed in adults and in children. The authors suggested that while each factor was localized to a different part of the brain, the regions work together as an organized system. “Sustained” attention was dependent on midbrain and brainstem; shifting with the prefrontal cortex; focused attention with the superior temporal cortex, inferior parietal cortex, and corpus striatum; and, encoding with the hippocampus and amygdala. Since Mirsky’s model was based on performance-based tests of attention, it translates easily to the clinical setting, and several computerized continuous performance tests for preschoolers have been developed and normed (see descriptions of tests below).
Attention and Executive Control Functions
There has been a concurrent interest in characterizing problems with attention and executive control functions in preschool children, driven in part by the increase in early identification of psychiatric and neurodevelopmental conditions (Espy, 2004). In the preschool years, these executive function skills have significant overlap with the developmental constructs measured in assessment of attention (Mahone, 2005; Mahone, Pillion, & Hiemenz, 2001; Mahone, Pillion, Hoffman, Hiemenz, & Denckla, 2005). Like their school-age counterparts, preschool children with attention problems may also present with significant executive dysfunction, although the pattern and trajectory of these behaviors in preschoolers may be different than that observed in school-age children (Arons, Katz-Leavy, Wittig, & Wayne Holden, 2002; Byrne, DeWolfe, & Bawden, 1998), with hyperactivity and impulse control (more than inattention and organization) observed as the primary problems (Byrne, Bawden, Beattie, & DeWolfe, 2000; Mahone et al., 2005; Mahone & Hoffman, 2007). This profile, however, may simply reflect what is demanded or expected of a preschool child. Like attention, individual characteristics of executive dysfunction change and are exhibited differently throughout development, from preschool through adult life (Root II & Resnick, 2003), and are elicited by environmental demands. Among preschoolers, however, both attention and executive function skills can be directly facilitated by provision of externally guided, attention-directing behaviors, usually initiated by the parent (Conway & Stifter, 2012).
A number of theories have attempted to capture the developmental overlap between attention and executive function. For example, Knudsen’s model of attention (Knudsen, 2007) emphasized the role of top-down control of both attention and behavior. The model suggests that there are four essential components of attention: working memory, competitive selection, top-down sensitivity control, and salience filters. Sensory information is filtered for what are either behaviorally important, instinctive stimuli, or infrequent stimuli in a bottom-up approach. The stimuli are encoded and go through competitive selection based on relative signal strength in order to determine what gets access to working memory. Working memory (a core executive function) uses the information to direct subsequent behaviors, as well as direct attention using a frontally mediated, top-down approach. The sensitivity of the information is regulated to improve signal-to-noise and attend only to the information relative to stimuli involved in necessary actions or judgments, and to selectively direct the necessary stimuli to be further encoded. Knudson argued that these tasks are dependent on the development of the prefrontal cortex.
Barkley’s model of executive function (Barkley, 2011a) also highlights the dynamic overlap between executive control and elements of attention. His theory emphasized the developmental unfolding of self-regulation and top-down control of behavior as a marker of prefrontal cortex development, and cites at least six key executive functions: self-restraint (executive inhibition), self-directed sensory-motor action (nonverbal working memory), self-directed private speech (verbal working memory), self-directed emotion/motivation (inhibition of strong emotions), self-directed play (planning, innovation, generativity), and self-directed attention (self-awareness). As a theory with a more direct link to top-down control, Barkley’s model has been linked more directly to ADHD than to disorders in which bottom-up or posterior attention systems are more affected. While performance-based tests of the model have been developed, their ecological validity has been criticized, and Barkley has emphasized the importance of rating scales for measuring elements of the model (Barkley, 2011b).
Recently, Dennis and colleagues (Dennis, Sinopoli, Fletcher, & Schachar, 2008) highlighted the importance of situational factors in determining the relationship between attention and executive function. Their model considered the integrated nature of stimulus orienting and response control, by considering the elements of each that are more related to attention networks (i.e., bottom-up), or to executive control networks (i.e., top-down). In their model, orientation to stimuli can occur as a result of a bottom-up (passive, external stimulus driven) or top-down (task driven, internally directed) approach. Response to stimuli can occur in a preprogramed, model-driven, performance and reward-based approach (bottom-up), or in a more top-down approach using instructions and attention priorities. In both stimulus orientating and response control, the individual is involved in three (potentially simultaneous) cognitive processes: activation (directing specific attention), inhibition (voluntary or automatic avoidance or cessation of response), and adjustment (performance monitoring and contingency adjustment), all of which interact dynamically to produce goal-directed behaviors.
Attention and Brain Development in Preschoolers
Development of the human nervous system begins 2–3 weeks after conception (Black, DiCicco-Bloom, & Dreyfus, 1990). Brain systems underlying attentional control are among the earliest to develop, with continued maturation into at least early adulthood (Gogtay et al., 2004). The trajectory of functional development, however, is nonlinear, and progresses in a region-specific manner that coincides with maturation of different brain systems (Halperin & Schulz, 2006). By age 2 years, the brain is approximately 80% of its adult size (Giedd et al., 1999). Subsequently, synapse formation (Huttenlocher & Dabholkar, 1997) and myelination (Kinney, Brody, Kloman, & Gilles, 1988) proceed rapidly up to age 2 years, followed by a plateau phase, during which neurons begin to form complex dendritic trees (Mrzljak, Uylings, Van Eden, & Judas, 1990). Maximum synaptic density (i.e., synaptic overproduction) is observed at age 3 months in the primary auditory cortex, but not until age 15 months in the prefrontal cortex (Huttenlocher & Dabholkar, 1997). After age 5 years, brain development is marked by continued neuronal growth, experience-dependent pruning of inefficient synapses, and cortical organization (Gogtay et al., 2004), with eventual reduction of synaptic density to 60% of its earlier maximum (Huttenlocher & Dabholkar, 1997).
Functional development of attention in the preschool years occurs via a process of active neural development—largely genetically determined—but also through a dynamic process of shaping and constraining abilities through experience, potentially modifying genetic expression (Blair & Raver, 2012). The idea of experiential canalization, described by Gottleib (1991), notes that functional development is shaped concurrently by biology as well as experience (or opportunity). In normal development, this “shaping” occurs via progressive myelination and associated cortical thinning, and is associated with improvements in attentional control. Conversely, pathological pruning (affected in part by experience) may contribute to the disrupted development of attentional skills (Kotrla & Weinberger, 2000; Marsh, Gerber, & Peterson, 2008), including ADHD (Sowell, Thompson, Welcome, Henkenius, Toga, & Peterson, 2003; Shaw et al., 2007).
The prefrontal cortex, which has a prominent role in the development of controlled (top-down) attention, has a protracted period of development, with rapid changes beginning in the first year of life (Diamond, 2002), that continue into young adulthood (Luna et al., 2001). There is evidence that maturation of the prefrontal cortex and its connections during infancy sets the stage for emergence of many “higher” cognitive processes, including top-down control of attention (Colombo & Cheatham, 2006; Kraybill & Bell, 2012). Prefrontal development in infancy and toddlerhood has been most commonly measured via electrophysiology (EEG; Fox, Schmidt, Henderson, & Marshall, 2007), such that frontal EEG power (considered a measure of neuronal excitability) is observed to be associated with controlled attention in toddlers (Morasch & Bell, 2011).
Over the first year of life, the development of attention is most commonly assessed behaviorally using visual attention paradigms (Columbo, 2001). In the first three months of life, infants are visually attracted to objects with contours and/or edges (e.g., faces, checkerboards), and exhibit long visual fixations. During this period, infants have difficulty disengaging visual attention from objects. This difficulty is likely because the pathways from the basal ganglia to the superior colliculus have begun to develop at that time, whereas the parietal lobes have yet to mature (Hood & Atkinson, 1993). Experimental paradigms used in infancy often include habituation and paired comparison, variants of which have been incorporated into infant development scales (e.g., Bayley Scales of Infant and Toddler Development, Third Edition; Bayley, 2006). Object novelty preference typically begins to emerge in infants around age 4–6 months, and is thought to coincide with the maturation of the cortical visual system and the parietal cortex. During this period, infants’ visual gaze time decreases and visual disengagement occurs. By 7–12 months, gaze time begins to increase again, and is accompanied by a shift from involuntary to more voluntary control, which continues to develop throughout toddlerhood and the preschool years (Columbo, 2001).
The development of neural systems supporting attentional control occurs at different rates in boys and girls (De Bellis, 2001). At birth, girls are already considered to be 3 weeks ahead of boys in terms of physical maturation; 1 year ahead by school entry (Eme, 1992). Although there are few reported sex differences in problem behavior in infancy and early childhood; sex differences appear to emerge by age 4 years, with boys showing more aggressive and impulsive behaviors. The change in behavior among girls may be a function of more rapid neurobiological, cognitive, motor, and social development, which, in preschool, may be protective against the manifestation of some ADHD symptoms in early childhood (Biederman et al., 2008). Sexual dimorphism in cerebral development may also contribute to the observed differences in attention problems. Giedd and colleagues compiled normative growth curves, demonstrating the sexual dimorphism in brain development (Lenroot et al., 2007). From age 4 to 20 years, linear increases in white matter volume with age were observed, whereas age-related changes in gray matter were nonlinear, regionally specific, and differed for boys and girls. Total cerebral gray matter volume was 10% larger in boys, but peaked much earlier in girls than boys (10.5 years vs. 14 years). The trajectory was identical for the caudate, which also showed peak at age 10.5 for girls and 14 for boys. Frontal lobe gray matter volume peaked around 10.5 years for boys (9.5 years for girls), and declined during post-adolescence resulting in an overall net decrease across the age span. Results were similar for parietal lobe volumes and differed only in that the slope of the curve was steeper and volumes peaked 1.5 years earlier for each sex (9.0 years for boys, 7.5 years for girls). Similarly, temporal lobe volumes peaked age 11 years for boys and 10 years for girls.
Interventions for Attention Problems in Preschoolers
A variety of programs have been developed to target improvements in behaviors associated with ADHD, including inattention and self-control. Two such programs, Triple P (Bor, Sanders, & Markie-Dads, 2002) and The Incredible Years (Jones, Daley, Hutchings, Bywater, & Eames, 2008), which emphasize parent training, have been shown to be effective in reducing disruptive behaviors, more so than behaviors associated with attentional control (Halperin, Bedard, & Curchack-Lichtin, 2012). Similarly, in a randomized control trial of a treatment program for preschoolers focusing on self-regulation and mother-child interactions (i.e., the Revised New Forest Parent Programme), the authors reported a reduction in symptoms associated with ADHD up to 9 weeks after conclusion of treatment (Thompson et al., 2009). More recently, Halperin and colleagues (Halperin et al., 2012) recently developed a novel method for training attention and other cognitive skills in preschoolers that has shown initial promise. Their Training Executive, Attention, and Motor Skills program utilized parent-directed small groups (3–4 parent-child dyads), that employed “games” emphasizing attention, inhibitory control, working memory, planning, visuospatial skills, and motor skills. Groups occurred daily for 30–45 minutes, and treatments lasted approximately 5–8 weeks. Preliminary evidence suggested that parent and teacher ratings of attention improved (relative to baseline) after completion of treatment, with gains maintained at three-month follow up (Halperin et al., 2012).
The practice of prescribing psychotropic medications for very young children has increased in both the US and Europe (Connor, 2002). For example, Rappley, Eneli, & Mullan (2002) reported on 223 children age 3 years and younger who were receiving treatment for attention problems. More than half of their sample received treatment in an idiosyncratic manner, and had monitoring less than once every three months. In an attempt to improve knowledge about assessment and treatment of attention problems in young children, the NIMH began a clinical trial in 2000 to study the effects of methylphenidate in preschoolers (ages 3–6 years) with ADHD. This study, known as the Preschool ADHD Treatment Study (PATS) has begun to shed light on diagnostic methods and treatments for ADHD and other attentional disorders in the preschool years (Vitiello et al., 2007), including safety of stimulants (Greenhill et al., 2006), short-term (Abikoff et al., 2007) and long-term effectiveness (Vitiello et al., 2007), and associated side effects (Ghuman et al., 2001), including reduced growth rates among preschoolers treated with stimulants (Swanson et al., 2006). In one sample of preschoolers with ADHD treated with stimulant medication, more than 82% of the sample saw improvement in behavior ratings by at least one standard deviation (Short, Manos, Findling, & Schubel, 2004). The presumed mechanism of action of stimulants, which has been established via studies of older children and adults (but not among preschoolers), is by increasing the availability of catecholamines (especially dopamine and norepinephrine) in the synaptic cleft (Plizska, 2007). Given the preponderance of these neurotransmitters in the fronto-striatal circuitry, stimulants have primary action on attentional functions affecting top down control, and improvement in these skills has been observed in preschool children (Abikoff et al., 2007). From these studies, the American Academy of Pediatrics has recently addressed the use of stimulant medication in preschool children (ages 4–5 years), and has recommended using stimulant medications only in those preschool-aged children with symptoms of ADHD who have moderate-to-severe symptoms that have persisted for at least 9 months, with dysfunction manifested in both the home and other settings such as preschool or child care, and who have not responded adequately to behavior therapy (AAP, 2011).
To date, there have been only two published studies of pharmacological treatment of preschool children with non-stimulant medication—both with atomoxetine, a selective norepinephrine reuptake inhibitor. An open-label study of atomoxetine (titrated to 1.8 mg/kg/day) with 12 preschool children ages 3–5 years showed adequate tolerability and reduction of parent reported hyperactivity and impulsivity from baseline (Ghuman et al., 2009). More recently, a larger, 8-week, double blind, placebo-controlled, randomized clinical trial of atomoxetine (titrated to 1.8 mg/kg/day) in 101 children with ADHD (ages 5–6 years) led to significant reductions in core symptoms of inattention (observed by parents and teachers) and hyperactivity (observed by parents), although functional impairment was not significantly affected (Kratochvil et al., 2011). Given the findings from pharmacological studies of preschoolers, it is clear that behavioral treatments are necessary to augment any medication therapy treatment in this age range.
Methods for Assessing Attention in Preschoolers
Comprehensive assessment of attention and related functions in children should include thorough review of the child’s history, planned observations, and formal psychometric testing (Mahone & Slomine, 2008). The three primary methods of psychometric assessment that have been used to characterize attentional functioning in preschool children include performance-based tests, rating scales (parent, teacher, clinician), and structured interviews. Performance-based methods for measurement of attention in the preschool years have been developed to address most of the salient components of attention described by Mirsky, Dennis, and Posner, and include sustained attention, selective (focused) attention, span of attention (encoding/maintaining), and top-down controlled attention, including freedom from distractibility and set-shifting. A review of published methods is provided below, and includes measures that are commercially available, and those that have been published only in the research literature.
Continuous Performance Tests
Kiddie Continuous Performance Test (K-CPT)
The K-CPT (Conners, 2001) is a computerized test of attention for children ages 4 and 5 years. The task lasts 7.5 minutes and uses 11 black and white pictures of common objects (10 targets, 1 non-targets). The child must respond by clicking a mouse or pressing space bar as quickly as possible following all pictures except for the non-target (a soccer ball). Data regarding omissions, commissions, perseverations, hit reaction time, and standard error are collected. Response time data are also used to determine response consistency as the task progresses, as well as in response to the two interstimulus intervals. The normative sample included 454 four- and five-year-old children, of whom 314 were classified as nonclinical, 100 as having ADHD, and 40 as clinical cases without ADHD. The nonclinical sample was relatively even in regard to sex distribution (48% boys, 52% girls); however, the majority of the ADHD sample was boys (75%). Split-half reliability ranged from .72 to .83 (Conners, 2001).
Despite its publication over a decade ago, there have been relatively few validity studies using the K-CPT. In one study combining the K-CPT (ages 3–5) and the CPT-II (Conners, 2000; ages 6–7), omission errors were significantly correlated with the Conners’ Parent Rating Scale-Revised (CPRS-R) Cognitive Problems and Inattention scales; although, commission errors were not found to be associated with the Hyperactivity scale (Rezazadeh, Wilding, & Cornish, 2011). Preschool children without behavioral difficulties are observed to have fewer omissions, lower reaction time standard error, less variability and less deterioration in performance over time than children with hyperactive and oppositional behaviors (Youngwirth, Harvey, Gates, Hashin, & Friedman-Weieneth, 2007). The K-CPT has also been used as an attention measure with healthy preschoolers in research comparing effects of DHA supplements on cognitive functioning (Ryan & Nelson, 2008).
Auditory Continuous Performance Test for Preschoolers (ACPT-P) (Mahone et al., 2001)
The ACPT-P is a computerized go/no-go test developed for use in children ages 36 to 78 months. Omissions, commissions, response latency, and variability of response time are the primary performance indices. This is a true go/no-go test, with only two stimuli—one target (dog bark) and one non-target (bell). Auditory stimuli are presented for 690 msec, with a fixed ISI of 5000 msec. During this five-minute test, 15 target and 15 non-target stimuli are presented. The child presses the space bar immediately following the target stimulus, and ignores the non-target. Initial studies showed no significant differences between typically developing boys and girls on any of the indices. Performance (omissions, response latency, and variability) improved with age from age 3–4 years, leveling off by age 5 years and was correlated with parent ratings on the CPRS-R (Mahone et al., 2001). Preschool children with ADHD demonstrate significantly poorer performance on the ACPT-P with regard to omissions, mean response time, and variability (Mahone et al., 2005). Among preschoolers with ADHD, the ACPT-P omissions, response time, and variability were significantly associated with performance on the NEPSY Statue test (Mahone et al., 2005). Among typically developing preschool children, amount of nighttime sleep was significantly (inversely) associated with number of commission errors on the ACPT-P (Lam, Mahone, Mason, & Scharf, 2011).
Continuous Performance Task for Preschoolers (CPTP) (Corkum, Byrne, & Ellsworth, 1995)
The CPTP is a computerized test designed for children ages 3–5 years. The CPTP uses pictures for stimuli, includes targets and distractors, a sequential presentation of stimuli in a quasi-random fashion, a slowed rate of presentation to allow for longer viewing time, a longer response window, fewer trials to reduce total task duration, and a training phase (Corkum et al., 1995). All six stimuli (1 target, 5 non-targets) are black and white, hand drawn (and scanned) figures with the same basic circular shape. Non-targets include pictures of a girl’s face, the sun, an ice cream cone, a lollipop, and a flower; the target is a pig face. The test presents 240 stimuli (40 targets) in pseudorandom order in which the target and each non-target occur once every six trials. For evaluation purposes, the session is divided into four 60-trial blocks, and the total test is 9 minutes long. Omissions, commissions and response latency are recorded.
In a sample of 60 typically developing preschoolers, an increase in omissions was observed over the 9-minute course of the CPTP. In all blocks, 3-year-olds showed more omissions than 4- and 5-year-olds; however, only in the last three blocks did 4-year-olds display more omissions than 5-year-olds. A greater number of commissions were displayed by 3-year-olds than by the other two groups, and boys displayed more commissions than girls. The sensitivity to target discrimination improved with age as well. When compared with other measures of preschool attention, commissions and omissions on the CPTP were significantly correlated with performance on a preschool picture cancellation test (Corkum et al., 1995).
Hagelthorn and colleagues (Hagelthorn, Hiemenz, Pillion, & Mahone, 2003) adapted the CPTP by shortening the length to three minutes and reducing the number of non-targets to one to facilitate more direct comparison with a preschool auditory CPT (i.e., the ACPT-P described above). In this adaptation, stimulus duration and interstimulus intervals remained identical to those described by Corkum et al. (1995). In this sample, typically developing children displayed a significantly higher rate of omissions and commissions on the visual task than on the auditory task. Mean reaction time and omissions errors decreased with age. Of note, the findings from the Hagelthorn study suggested that 3-year olds likely require interstimulus intervals as long as 5000 msec in order to respond within the allotted interval (and not to the preceding stimulus).
The CPTP has also been used in preschool children with ADHD. In a sample of 50 children ages 3–6 years, children with ADHD made more errors of omission and commission than age-matched typically developing peers (DeWolfe, Byrne, & Bawden, 1999). Preschoolers with ADHD who had not been treated with stimulant medications had significantly more omissions and commissions on the CPTP than matched controls; however, once treated, group differences were eliminated (Byrne et al., 1998). Noland and colleagues also used the CPTP to investigate attention in 4-year-olds who had experienced prenatal substance exposure (Noland et al., 2005). The authors reported that children with prenatal cocaine exposure “passed” the pretest portion of the CPTP at a significantly lower rate than non-exposed children. Additionally, cocaine-exposed and cigarette-exposed children display significantly more commission errors than non-exposed children, and increased exposure to cigarettes was associated with a higher rate of commission errors. Severity of marijuana exposure showed a positive, but non-significant correlation with omission errors.
Zoo Runner was developed by Prather, Saramento, and Alexander (1995) to assess sustained attention in children ages 3 to 6 years. It has two components: an auditory attention task and a visual task. On the auditory test, animal sounds are presented to the child for 1000 msec, and with an ISI of 1000 msec. There are a total of 215 trials, and the task takes 7.2 minutes. There is 1 target and 11 non-target stimuli. Children are asked to press a button when they hear the word “tiger.” Mean reaction time, omissions, and commission errors were recorded. The auditory version of Zoo Runner has been used in both clinical and nonclinical samples. In a sample of 50 children ages 3–6, children with ADHD had similar rates of omissions and commissions on this task compared with typically developing peers (DeWolfe et al., 1999). Similar to the CPTP, preschoolers with ADHD who had not been pharmacologically treated displayed significantly more omissions on the auditory Zoo Runner task than matched controls; however, once treated, this difference was eliminated (Byrne et al., 1998).
The visual version of Zoo Runner requires the child to respond after seeing a picture of a cat. Stimulus presentation time, interstimulus intervals, total number of trials, number of targets and non-targets, and total task duration are the same as in the auditory version. In both tasks, typically developing children were noted to improve with age on omissions, commissions, and reaction times. Children at age 3 years demonstrated a higher number of omissions on both tasks, suggesting that the tasks may be too difficult for typical children of that age. After age 5.5 years, little further improvement is observed (Prather, Sarmento, & Alexander, 1995).
Children’s Continuous Performance Test (C-CPT) (Kerns & Rondeau, 1998)
The C-CPT is a computerized CPT that uses a combined visual/auditory format. Stimuli are presented at 1500 msec intervals—one target for every six non-targets, for a total duration of 5 minutes. Familiar animal pictures are paired with the common noise associated with those animals. Familiarization to the pictures and sounds are completed prior to test administration, and a practice trial is administered until 100% accuracy is obtained. Correct hits, omission errors, commission errors, and reaction times are recorded. Three subtests can be administered to each participant, for a total of 200 stimuli, including 29 randomly presented targets. Task 1 presents the visual and auditory pairing, during which the child is asked to respond to the sheep. Task 2 presents only the audio stimuli (with an X on the screen), and the child is again asked to respond to the sheep sound. Task 3 pairs the visual and auditory stimuli incorrectly, and the child is asked to respond to the picture of the sheep, regardless of the accompanying animal sound.
When administered to typically developing children ages 40 through 64 months, a significant age effect was found for correct hits on all three tasks, and for commission errors on Task 1. Correct hits increased as age increased, while commission errors decreased with age. As a group, children displayed fewer overall hits on Task 2 (auditory only) than on Tasks 1 and 3, suggesting that the task may have been more difficult. More commission errors were made on Task 3 (incorrect pairings) than on Tasks 1 or 2. Reaction times across all three tasks were faster for commission errors than for correct hits. No significant effects of sex were identified (Kerns & Rondeau, 1998). Among clinically-referred preschoolers with attention problems, only 39% had successful completion of all three C-CPT trials (compared with 98.9% control completion), despite all clinical participants being able to complete the practice trial successfully, suggesting that only Task 1 is appropriate for use in clinical groups (Kerns & Rondeau, 1998).
The Preschool-Continuous Performance Test (P-CPT) is a modification of the C-CPT, and includes only Task 1. The child is told that he or she is responsible for feeding the sheep, and must do so by touching the sheep when it appears on the computer screen. The child is not supposed to touch any of the other animals. The task is 5 minutes in duration, includes 200 stimulus presentations, of which 29 are sheep. Omission errors, commission errors, and reaction times are recorded. In a sample of typically developing children ages 3–5 years from private preschools in a socio-economically disadvantaged area of Canada, correct hits (.65), omissions (.63), and reaction time (.77) were all found to display modest test-retest reliability while commission errors had less stability (.44) (Muller, Kerns, & Konkin, 2012). Preschool children with both early and late pre-term birth made significantly more errors of omission and commission than age-matched term birth children (Baron, Kerns, Muller, Ahronovich, & Litman, 2011).
Gordon Diagnostic System (GDS) (Gordon, McClure, & Post, 1986)
The GDS is a self-contained computerized CPT that is most often used with children of school age or adults; however, it can also be used with 4- and 5-year-old children. Normative data for the GDS were collected during the mid-1980s., with data based on more than 1250 children aged 4 to 16 years old (Gordon & Mettelman, 1987). Preschool children (4–5 years-old) are asked to complete two tasks—Delay and Vigilance. On the Delay task, the child is instructed to earn maximum points by pushing a button; however, a delay between presses is required in order to earn points. The child must determine how long to wait, as well as be able to wait that amount of time between presses in order to earn points. Typically, a 6-second delay is required; however, this is decreased to 4 seconds for preschool children. If the child responds sooner than 4 seconds, a buzzer sounds and the timer is reset; however if they wait the 4 seconds before responding, a light flashes and a point is earned. The delay task is 6 minutes in duration. The percentage of correct responses (efficiency ratio) is used to determine the child’s level of impulsivity. The Vigilance task is also modified for children ages 4 and 5 years. Rather than the standard 1/9 combination required for response with older children, the preschool task assesses sustained attention by flashing numbers quickly on the screen and asking the child to respond when a 1 appears. The presentation interval is 2 seconds, and the entire task lasts 6 minutes. Performance is evaluated using the total correct and the total number of commissions.
Mariani and Barkley (1997) used a version of this task with 4- and 5-year old boys in which they extended the standard duration time from 6 minutes to 9 minutes and used the single digit target of 7. Boys with ADHD performed significantly worse on the total correct responses, but not on commission errors. Similarly, Pulsifer and colleagues used the GDS to assess attention in 5-year-old children living in an urban environment, with and without prenatal drug exposure. The authors reported that the drug exposed group had significantly fewer commission errors, although both groups performed below average in regard to sustained attention (Pulsifer, Butz, O'Reilley, Belcher, 2008).
Preschool Vigilance Task (PVT) (Harper & Ottinger, 1992)
The PVT is a computerized task that presents a picture of a tree with an extended right-side branch. A bird appears on the branch for 0.5 seconds 25 times at intermittent intervals ranging from 10 to 60 seconds, for total task duration of 14.5 minutes. The ISIs are chosen randomly, but each participant receives the same sequence. The child is instructed to press the response button only when the bird appears on the tree. The computer records errors of commission, errors of omission, and reaction time. This task was evaluated on a sample of 20 hyperactive 4–6 year olds, predominantly boys, and 20 controls matched on gender and age. Errors of omission demonstrated high test-retest reliability (.80); however, commission errors and reaction time did not. Hyperactive children tended to make more errors of omission, but not commission, on the PVT. The PVT was able to correctly classify hyperactive versus typically developing with 82.5% accuracy (Harper & Ottinger, 1992).
Additional Issues with Preschool CPT Tests
Other continuous performance tasks have been developed that assess sustained attention in preschoolers with and without ADHD, as well as with and without other childhood disorders. Some researchers have adapted tasks designed for older children to be more appropriate for preschool groups, for example, by decreasing the total task duration and using more basic stimuli (Finneran, Francis, & Leonard, 2009). Even with these adaptations, other factors, such as ISI can impact performance (Finneran et al., 2009; Hagelthorn et al., 2003). In a study of preschool children described as low or high risk for ADHD Berwid and colleagues manipulated the ratio of targets to non-targets in a computerized test. Across groups, rates of omission and commission errors decreased with age and the youngest group displayed significantly more errors than the middle and oldest age groups (which did not differ). An interaction effect was observed, such that group differences in commission errors diminished with age. High-risk children also displayed longer and more variable reaction times, though again, mean response time and response time standard deviation decreased with age when comparing the youngest group (ages 3.44 to 4.54) to the older two groups (ages 4.54–5.57, and 5.58–6.95). The greatest response time discrepancies between risk groups were found to be present in the youngest age groups (Berwid, Curko, Marks, Santra, Bender, & Halperin, 2005). Another common problem is that some CPT tasks for preschoolers use letters or numbers as stimuli (Harper & Ottinger, 1992), which presumes the children taking the test have automaticity of recognition of their letters and numbers.
A summary of the CPT tests reviewed is provided in Table 1.
Preschool Continuous Performance Tests
Visual Cancellation Tasks
Picture Deletion Test for Preschoolers (PDTP) (Corkum et al., 1995)
The PDTP presents a quasi-randomized matrix of picture targets and non-targets, and reduces fine motor demands (compared with traditional paper and pencil tasks) via use of a self-inking “bingo” stamper (Corkum et al., 1995). Normative data were collected on 60 Caucasian children ages 3–5 years. Sex distribution in each age group was relatively equal. The PDTP requires the child to search a visual array of targets and non-targets to locate and mark the targets as quickly as possible. The training phase involves teaching the child to identify and mark the appropriate target. The test phase involves four tasks: Geometric Shape Deletion, Cat Deletion, Fish Deletion, and Motor Deletion. The total test phase lasts approximately 10 minutes. The first three tasks include one Discrimination and two Deletion phases. The Discrimination phase is used to determine that the child is able to identify an example of each distractor and the target. In the Deletion phase, the child is presented with two adjacent 10-inch × 6-inch arrays of 15 target and 45 non-target pictures, with an example of the target at the top, and asked to mark the targets as quickly as possible. Performance is measured in time to completion (speed), errors of omission, and errors of commission (accuracy). The Motor Deletion Task assessed the speed of marker use by presenting a single 10-inch × 6-inch array of circles and asking the child to mark all of the circles as quickly as possible.
Across the three age groups, more commissions were observed on the Fish trial than the Cat trial. Three-year olds made more omissions on the Cat trial than on the Shape trial. No significant differences between age groups were observed in regard for omissions and commissions on the Shape trial; however, 3-year olds made more omissions than 4-year-olds on the Cat trial, and the number of omissions decreased on the Fish trial as children got older. Similarly, commissions decreased with age on the Fish trial as well. Age effects were observed in regard to commissions on the Cat trial in the younger two groups as well, with 4-year-olds performing better than 3-year-olds. Performance on the Cat and Fish trials of the PDTP were significantly associated with commission and omission error rates on the CPTP (Corkum et al., 1995).
A revised version of the PDTP has been published, with removal of the Fish trial, an increase in the number of Cat trial arrays, and change in the printed layout of the task (Byrne et al., 1998). Using the revised task in a clinical sample of 50 children with ADHD, ages 3–6 years, there were no group differences (compared with age-matched controls) on the PDTP for omission errors; however, the ADHD group made significantly more commission errors and displayed a longer latency to task completion (DeWolfe et al., 1999). Additionally, preschoolers with ADHD who had not been treated with stimulant medications displayed significantly more commission errors on the PDTP than matched controls; however, once treated, there were no longer group differences (Byrne et al., 1998). The PDTP has more recently been used to assess attention in 4-year-old children with prenatal substance exposure. The children with prenatal cocaine exposure “passed” the pretest portion of this task at a significantly lower rate than non-exposed children. Additionally, preschool children with prenatal tobacco exposure produced a higher rate of commission errors than non-exposed children (Noland et al., 2005).
NEPSY Visual Attention (Korkman, Kirk, & Kemp, 2007)
The original version of the NEPSY was designed to assess neuropsychological development of children ages 3 to 12 years. NEPSY subtests were divided into five content Cores—one of which one was Attention/Executive Functions. The Visual Attention subtest was included in this Core. Only two of the subtests on the NEPSY Attention/Executive Function Core were designed for use with preschool children—Visual Attention and Statue. Both of these measures have been used in studies of preschoolers with symptoms of ADHD (Mahone et al., 2005; Youngwirth et al., 2007), and in evaluating attention in other clinical groups, such as those with exposure to gestational diabetes mellitus (Nomura et al., 2012). The NEPSY Visual Attention subtest is a visual cancellation task that assesses the child’s ability to use selective focus and attention, along with speed and accuracy. The task requires the child to identify and mark the target stimulus among an array of distractors as quickly as possible. For preschoolers, there are two trials: bunnies (arranged in rows) and cats (arranged in random order). The child is required to search the pages and mark each target (which is represented at the top of the page) with a red crayon. Each trial is 120 seconds. Published reliability coefficients for children ages 3–5 years ranged from .68 to .76. In a sample of 184 typically developing children ages 3½ to 6 years, a moderate association was observed between the NEPSY Visual Attention and Statue subtests in children with a verbal span of ≤ 3 digits, but no relation in children with digit span of ≥ 5 (Espy, 2004). Unfortunately, the Visual Attention subtest was not included in the second edition of the NEPSY due to concerns about insufficient clinical sensitivity (Korkman, Kirk, & Kemp, 1998).
Visual Search Task (Visearch; Wilding, Munir, & Cornish, 2001)
This is a visual selection task designed for children ages 3–7 years. The task has two conditions, the single-target search condition and the dual-target search condition. In this task, participants were seated in front of a screen showing a display of black and brown color “holes” of different shapes on a green background with a river and some trees. In the single-target search condition, participants were instructed to touch a hole of prior specified shape and color (e.g., black vertical ellipse or a brown horizontal ellipse) in order to uncover the “king of monsters.” Participants are instructed that small monsters (which are blue for black vertical ellipses and yellow for brown horizontal ellipses) will pop from the target holes, but they have to continue looking until the king of monsters was found. The king always appears on the twentieth target touched. Performance is assessed using the number of false alarms to non-target holes and mean response time per hit. A modified version of the original task was used by Wilding et al. in which the “holes” were larger than in the original version, measuring 8 mm or 6 mm in diameter, with the same measurements for the longer and shorter axes of the ellipses. There were 20 targets in the single-target searches and 15 for each target in the dual-target search. Non-targets were large or small circles and ellipses in both colors; there were 50 non-targets in the single search conditions and 40 non-targets in the dual search condition, making 70 objects in all (Wilding et al., 2001).
Additional Performance-based Tests of Attention
Statue (Korkman et al., 1998; Korkman et al., 2007)
The NEPSY Statue subtest assesses motor persistence and inhibition by asking the child to close his or her eyes, remain in a specified body position, and refrain from speaking or laughing for 75 seconds while the examiner performs potential distractions (e.g., dropping a pencil). The published reliability coefficient for the original NEPSY among children ages 3 to 4 years was only .50; nevertheless, the Statue test has been found to be highly sensitive in clinical groups. Preschoolers (ages 3–5 years) with ADHD were observed to have lower Statue scores than age- and sex-matched controls (Mahone et al., 2005), while preschoolers with behavior problems had lower Statue performance than those without behavior problems (Youngwirth et al., 2007). In the revised NEPSY (NEPSY-II; Korkman et al., 2007), normative data have been updated and the Statue subtest is administered in exactly the same manner as in the first edition. In the NEPSY-II, the reliability coefficient for children ages 3–4 years on the Statue subtest is considerably improved (.82) (Korkman et al., 2007).
Recognition of Pictures (Differential Ability Scales-Second Edition—DAS-II; Elliott, 2007)
The DAS-II was standardized on a sample of 3,480 children, ages 2:6 through 17:11, stratified by six-month age groups for ages 2, 3, and 4, and one-year age groups for ages 5 through 17. A total of 880 children between the ages of 2:6 and 4:11 were included. On the Recognition of Pictures subtest, the child is presented with pictures of common objects for 5 seconds. This is followed by presentation of a different page, on which the target object(s) is presented with similar distractor items. The task requires the child only to point to the target object(s) to identify the target. The number of target items gradually increases, as does the similarity of the targets to the distractor items. Reliability coefficients for the Recognition of Pictures task for children ages 2:6–5:11 range from .77 to .85 (Elliot, 2007). The task assesses short-term recognition memory, which is highly dependent on focused (selective) attention and visual attention span. School-age children with ADHD have been shown to have poorer performance on the Recognition of Pictures test, compared to controls (Weisen, 2008); however, there is little literature supporting its validity among preschoolers.
Digit Span Measures
There are two similar digit span measures that have been published and normed for preschool aged children. Both assess auditory verbal attention span (i.e., the “encode” component of attention described by Mirsky and colleagues). The first is Number Recall (Kaufman Assessment Battery for Children—KABC-II; Kaufman & Kaufman, 2004). The KABC-II was standardized on a sample of 3,025 children, stratified by six-month age groups in ages 3 and 4, and one-year age groups for ages 5 through 18. The Number Recall task requires the child to repeat series of single syllable numbers of increasing length. The numbers in the series are presented orally at a rate of one per second. The series of numbers on the original KABC ranged from two to eight, but was expanded to include nine-digit sequences on the KABC-II. Reliability coefficients for the Number Recall task of the KABC-II for children ages four and five are .87 and .79, respectively (Kaufman & Kaufman, 2004). There is significant improvement in performance among typically developing controls between ages 3–4 years; with slower rate of improvement between 4–5 years (Lam et al., 2011). Mariani and Barkley (1997) reported that preschool boys with ADHD (ages 4–5 years) had significantly lower scores on the Number Recall subtest compared to controls. Among typically developing preschool children in fulltime daycare, the amount of daytime napping was significantly associated with performance on Number Recall (Lam et al., 2011).
The second digit span test for preschoolers is the Recall of Digits Forward (Differential Ability Scales - Second Edition- DAS-II; Elliott, 2007). The DAS-II was standardized on a sample of 3,480 children, ages 2:6 through 17:11, stratified by six-month age groups for ages 2, 3, and 4, and one-year age groups for ages 5 through 17. A total of 880 children between the ages of 2:6 and 4:11 were included. Similar to the KABC-II Number Recall task, the Recall of Digits Forward task requires the child to repeat a series of digits of increasing length. The numbers in the series are presented orally at a rate of two per second in order to prevent rehearsal. The series length begins with 2 digits and gradually increases to 10 digits. There are five trials of each series length. Reliability coefficients for the Recall of Digits Forward task for children ages 2:6–5:11 range from .88 to .91. (Elliot, 2007). Differences have been observed on this task, such that children who were born premature at an extremely low birth weight perform more poorly on this task at age 3 than children who were born at term (Baron, Kerns, Muller, Ahronovich, & Litman, 2011).
Other Verbal Span Tasks
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