J Abnorm Child Psychol (2014) 42:1–6 DOI 10.1007/s10802-013-9825-x
Sluggish Cognitive Tempo in Abnormal Child Psychology: An Historical Overview and Introduction to the Special Section Stephen P. Becker & Stephen A. Marshall & Keith McBurnett
Published online: 24 November 2013 # Springer Science+Business Media New York 2013
Abstract There has recently been a resurgence of interest in Sluggish Cognitive Tempo (SCT) as an important construct in the field of abnormal child psychology. Characterized by drowsiness, daydreaming, lethargy, mental confusion, and slowed thinking/behavior, SCT has primarily been studied as a feature of Attention-Deficit/Hyperactivity Disorder (ADHD), and namely the predominately inattentive subtype/ presentation. Although SCT is strongly associated with ADHD inattention, research increasingly supports the possibility that SCT is distinct from ADHD or perhaps a different mental health condition altogether, with unique relations to child and adolescent psychosocial adjustment. This introductory article to the Special Section on SCT provides an historical overview of the SCT construct and briefly describes the contributions of the eight empirical papers included in the Special Section. Given the emerging importance of SCT for abnormal psychology and clinical science, there is a clear need for additional studies that examine (1) the measurement, structure, and multidimensional nature of SCT, (2) SCT as statistically distinct from not only ADHD-inattention but also other psychopathologies (particularly depression and anxiety),
S. P. Becker (*) Department of Psychology, Miami University, 90 North Patterson Avenue, Oxford, OH 45056, USA e-mail: [email protected] S. P. Becker Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA S. A. Marshall Department of Psychology, Ohio University, Athens, OH, USA K. McBurnett Department of Psychiatry, University of California, San Francisco, San Francisco, CA, USA
(3) genetic and environmental contributions to the development of SCT symptoms, and (4) functional impairments associated with SCT. This Special Section brings together papers to advance the current knowledge related to these issues as well as to spur research in this exciting and expanding area of abnormal psychology. Keywords ADHD . Attention deficit disorder . Attention-deficit/hyperactivity disorder . Comorbidity . Concentration deficit disorder . DSM-5 . History . SCT . Sluggish cognitive tempo Sluggish Cognitive Tempo (SCT) is characterized by behavioral symptoms such as drowsiness/sleepiness, seeming to be “in a fog,” daydreaming, mental confusion, slowness, physical hypoactivity/lethargy, and apathy. Given these descriptors, and as described in more detail below, it is not surprising that the study of SCT as a construct largely emerged from investigations of Attention Deficit Disorder (ADD), and, more recently, Attention-Deficit/Hyperactivity Disorder (ADHD). Given the clear association between SCT and ADHD, there has been ongoing and increasing interest in whether or not SCT is empirically distinct from dimensions of ADHD as defined by the fourth and fifth editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV and DSM-5 ; American Psychiatric Association [APA] 1994, 2013), as well as the degree to which SCT is itself associated with psychosocial functioning and impairment. Indeed, there has been a marked increase in the last dozen years in the number of studies examining SCT. In order to more clearly illustrate this rise of interest in the topic of SCT, a search of journal articles was conducted using PsycINFO, PubMed, and GoogleScholar databases. Articles that included “sluggish cognitive tempo” (or related terms such as “slow cognitive tempo”) in the title or abstract were identified, as
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were articles that did not mention SCT in the article title/ abstract but mentioned SCT (or related terms) elsewhere in the article. The number of articles identified in each of these two categories is displayed in Fig. 1. As shown, very few papers explicitly examined or even mentioned SCT between 1985 and 1999. Since 2000, however, there has been a clear and relatively steady increase in the number of studies that focus on SCT or mention SCT in the body of the paper. Many of the studies in this latter group make reference to SCT in the Discussion of the study findings, highlighting the growing awareness of, and interest in, SCT as an important area for research and clinical attention. It is within this context that the set of papers included in this Special Section were prepared. Before briefly reviewing the contributions included in the Special Section, we provide an historical overview of the study of the SCT construct.
An Historical Overview of SCT Conceptualizations of difficulties related to inattention, hyperactivity, and impulsivity have undergone several important changes, both before and after entering the psychiatric nomenclature as Hyperkinetic Reaction of Childhood in the DSM-II in 1968 (APA 1968). Although a detailed summary of the history of ADHD is beyond the scope of this article (see Barkley 2006, for a thorough review), the study of SCT is closely tied to the study of ADHD. Many early references to ADHD-like conditions in the literature, such as Heinrich Hoffman’s description of Fidgety Phil in 1865 (Stewart 1970) and George Still’s lectures in the Lancet in 1902 (Still 1902), emphasize overactivity and disinhibition as hallmark features of the disorder. However, even as early as 1798, a
Number of Articles
45 40
SCT in Article Text
35
SCT in Article Title and/or Abstract
30 25 20 15 10 5 0
Year of Publication
Fig. 1 Number of journal articles published in print or online between 1985 and 2012 that include sluggish cognitive tempo (SCT) in the article title/abstract (black fill) or the article body (diagonal line fill). Search was conducted using PsycINFO, PubMed, and GoogleScholar databases
medical textbook written by Alexander Crichton (Crichton 1798) described two forms of attentional deficits: one involving overarousal of attentional systems and the other involving underarousal and low levels of mental energy (see Palmer and Finger 2001). Study of this underactive form of inattention took a back seat to the study of children with observable hyperactivity and impulsivity (e.g., Laufer et al. 1957). However, work by Virginia Douglas in the 1970’s (e.g., Douglas 1972) stressed that inattention caused more impairment for these children than hyperactivity. Influenced by her work, the DSM-III (APA 1980) positioned inattention as the core symptom dimension under the diagnostic label of Attention Deficit Disorder (ADD; APA 1980). In addition, for the first time, the DSM-III allowed for the diagnosis of a subtype that presented without hyperactivity. This new subtype was formed primarily to encourage research on nonhyperactive presentations which, despite being observed clinically, had received little empirical attention (Milich et al. 2001). SCT took shape as a construct around this same time. Even as early as the 1960’s and 1970’s, individual SCT symptoms (e.g., daydreaming, drowsiness, lethargy, laziness in school) were included in broadband rating scales for children (e.g., Conners 1969; Peterson 1961; Quay and Quay 1965). However, whereas many studies indicated that inattention represented a separable dimension from hyperactivity (see Hinshaw 1987, for a review), SCT and other inattention items loaded together on a unidimensional inattention factor, such as the Attentional Problems-Immaturity subscale of the Revised Behavior Problem Checklist (RBPC; Quay and Quay 1965; Quay 1983) or the Inattentive-Passive subscale of the Conners Rating Scales (Conners 1969). Interestingly, the single inattention factor extracted from a wide item pool in a 1971 study by Dielman, Cattell, and Leeper was even labeled “Sluggishness” because it included SCT-like items (drowsiness, easily fatigued, easily confused, laziness in tasks, and passivity), yet, again, inattentive items (e.g., short attention span, inattentiveness to what other say, and distractibility) loaded with these SCT items. It was not until the mid-1980’s that empirical support for a SCT dimension separate from inattention emerged, led in large part by the work of Benjamin Lahey, Ph.D., and Caryn Carlson, Ph.D. (see Carlson 1986). Specifically, in a large, school-based sample, Neeper and Lahey (1986) replicated the often-found separation of inattention from hyperactivity; however, a factor labeled “Slow Tempo” also emerged that was comprised of sluggish, apathetic, lethargic, drowsy, and “in a world of his or her own” items. Soon after, Lahey et al. (1988) extracted a comparable sluggish tempo factor (with forgetful, sluggish, drowsy, and “difficulty following instructions” items) in a clinic sample, and found further that a three-factor model of hyperactivity–impulsivity, inattention– disorganization, and slow tempo provided the best-fitting model of ADD.
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It is important to note that this division of inattention into two dimensions also aligned with the division of ADD into two subtypes in the DSM-III during the same decade (APA, 1980). For instance, studies found that inattention subscales on commonly used rating scales such as the RBPC and the Child Behavior Checklist (CBCL; Achenbach and Edelbrock 1983) did not uniformly apply to both ADD subtypes. Children with ADD with hyperactivity (ADD/H) were uniquely elevated in attentional problems characterized by distractibility, sloppiness, carelessness, and irresponsibility items, whereas children with ADD without hyperactivity (ADD/noH) were uniquely elevated in attentional problems characterized by sluggishness, drowsiness, slowness, being “lost in a fog,” daydreaming, and apathy (Barkley et al. 1990; Lahey et al. 1985). Once factor analytic work had identified a distinct SCT factor, other studies found that SCT scores were uniquely elevated in children with ADD/noH as compared to children with ADD/H (Lahey et al. 1987, 1988). In an indirect fashion, the validity of SCT was supported by research showing that the two ADD subtypes were associated with a different pattern of external correlates. ADD/H was uniquely associated with higher levels of aggression, conduct problems, impulsivity, and peer rejection and lower levels of guilt, whereas ADD/noH was uniquely associated with higher levels of anxiety, unhappiness, shyness, and peer withdrawal and lower levels academic performance and math achievement (see Milich et al. 2001, for a review). Family psychiatric histories also differentiated the groups, as more ADD/H and substance abuse problems were reported in relatives of children with ADD/H and more anxiety and learning problems were reported in relatives of children with ADD/noH (Barkley et al. 1990). Although there were rarely differences between the two subtypes on neuropsychological tests (see Milich et al. 2001), some studies found that the ADD/H group exhibited greater problems with disinhibition (Barkley et al. 1991) whereas the ADD/noH group exhibited more problems with perceptual-motor speed, automatized processing, and inconsistent performance on a memory task (Barkley et al. 1990, 1991; Hynd et al. 1991). In 1987, the DSM-III-R eliminated the subtyping of ADD and instead created a single disorder named AttentionDeficit/Hyperactivity Disorder (ADHD; APA 1987). However, this decision to remove subtypes was short-lived, as the DSM-IV Work Group on Disorders Usually First Diagnosed in Infancy, Childhood, or Adolescence decided to revisit subtypes for the classification of ADHD. Influenced by the DSM-III ADD subtype validation research and SCT factor analytic work from the 1980’s, the DSM-IV work group considered incorporating SCT symptoms in the new diagnostic criteria for a reinstated nonhyperactive subtype of ADHD. The DSM-IV Options Book (APA 1991) proposed using two partially overlapping yet distinct sets of inattention symptoms to identify each of the subtypes: six overlapping symptoms
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(i.e., difficulty following instructions, difficulty sustaining attention, trouble listening, loses things, inattention to details, and disorganization), two symptoms unique to ADD/H (i.e., distractibility and shifts between uncompleted activities), and four SCT symptoms unique to ADD/noH (i.e., forgetfulness, daydreaminess, sluggishness/drowsiness, and apathy). Three of these SCT items–forgetfulness, daydreaminess, and sluggishness/drowsiness–were tested in the DSM-IV field trials. Although all three demonstrated strong positive predictive power (PPP), the daydreamy and sluggish/drowsy items showed poor negative predictive power (NPP), leading the work group to decide on a single, parsimonious list of inattention symptoms to be used for diagnosing both subtypes (Frick et al. 1994). Of the proposed SCT symptoms, only the forgetful item was included in the DSM-IV because it showed utility for both hyperactive and nonhyperactive subtypes (Frick et al. 1994). The exclusion of all but one SCT symptom from the DSM-IV ADHD criteria did not end interest in the construct. One reason for continued interest was that research examining the validity of DSM-IV subtypes was unconvincing (see Willcutt et al. 2012), and some thought that the DSM-IV diagnostic criteria for the new inattentive subtype (ADHD Predominantly Inattentive Type [ADHD-I]), which had been changed considerably from DSM-III criteria, identified too heterogeneous a group (McBurnett et al. 2001; Milich et al. 2001). Many cases with ADHD-I were found to have low levels of SCT, while a subset of others with ADHD-I showed high levels of SCT (Carlson and Mann 2002). Further, under DSM-IV criteria, individuals with up to 4 or 5 symptoms of hyperactivity-impulsivity could be diagnosed with ADHD-I, whereas many others diagnosed with ADHDI showed very few or no symptoms of hyperactivityimpulsivity (see Milich et al. 2001). This variability in ADHD-I was highlighted in a collection of commentaries in a 2001 issue of Clinical Psychology: Science and Practice , in which a number of ADHD experts argued that research into SCT could help specify an important dimension of attentional problems, as well as a distinct classification of attentional disorder (e.g., Milich et al. 2001). In conjunction with these commentaries, an empirical paper by McBurnett et al. (2001) replicated the factor analytic work of Lahey and colleagues from the 1980’s by extracting a similar SCT factor (forgetful, daydreams, sluggish/drowsy) in a large ADHD clinic sample. As illustrated in Fig. 1, this group of articles stimulated the growth in SCT research seen over the past dozen years. This growing body of research has focused on developing more comprehensive measures of SCT symptomatology and, in concert, using factor analysis to validate the internal and discriminant validity of the SCT construct. It is within this context of renewed interest in the measurement, validity, and correlates of SCT that this Special Section was prepared.
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Special Section Studies This Special Section includes eight empirical articles as well as a commentary by Russell Barkley, Ph.D. The empirical articles use an array of sample types and methodologies that together provide an important advance of the current literature. In the literature published up to this date, one of the most consistent findings regarding the internal validity of SCT is that it constitutes a latent factor that is separate from that of ADHD Inattention. Of the eight papers herein, four (Becker et al. 2014, this issue; Lee et al. 2014, this issue; McBurnett et al. 2014, this issue; Willcutt et al. 2014, this issue) evaluated internal consistency with various methods. All four replicated the general finding that SCT represents a distinct latent factor. Thus, this particular question—is there such a thing as SCT that is different from ADHD Inattention—seems to be laid to rest as of this issue of JACP because of the consistency with which a separate SCT factor is extracted across methods and data sets (note that recent studies also document SCT to be distinct from ADHD in adults; Barkley 2012; Becker et al. 2013). Another question in this literature is whether SCT is a different construct from internalizing problems in general, and from depression more specifically. Three of the papers (Becker et al. 2014, this issue; Lee et al. 2014, this issue; McBurnett et al. 2014, this issue) pose this question from different approaches. Overall, the findings suggest that SCT and internalizing disorder symptoms are indeed distinct, and that impairment correlated with SCT is not fully explained by the presence of internalizing symptoms. However, to complicate matters, some authors found that items indicating low activity, speed, or energy levels have the potential to confound SCT and depressive factors. It may be that behaviors related to sluggishness, a cardinal indicator of SCT, may in fact be a clinically observable feature of SCT, while at the same time such behaviors may not be helpful in measures of SCT when discriminant validity is the goal. SCT may be of little consequence if it can only be shown to be psychometrically distinct from ADHD and other psychopathologies but does not also predict meaningful external constructs. Nearly all of the papers in this Section, including those cited above as well as those from Langberg et al. (2014, this issue), Marshall et al. (2014, this issue), and Watabe et al. (2014, this issue) report on the external correlates of SCT. A key finding is that some first-order associations that do not seem to make sense—such as the positive associations of SCT with ADHD hyperactive-impulsive and oppositional defiant disorder (ODD) symptoms—seem to become nonexistent (or negative in direction) when other psychopathology dimensions such as ADHD inattention are also included in the model (Lee et al. 2014, this issue). Turning to impairment, the general finding of papers in this Special Section is that SCT adversely impacts some aspects of social and academic
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functioning, even when the contributions from ADHD symptoms are controlled. Watabe et al. (2014, this issue) provide the exception: depending on informant and context (school vs. home), SCT could appear adaptive or maladaptive. Future resolution of this conundrum might take into account the inverse association of SCT with ODD symptoms or behavioral dysregulation once other psychopathology symptoms are controlled (Becker et al. 2014, this issue; Lee et al. 2014, this issue), and the report from Weinberg and Brumback (1990) that children with Primary Disorder of Vigilance (a clinical syndrome with some resemblance to SCT) are unusually sweet and well-behaved. Likewise, it is possible that SCT represents a type of pathological mind wandering (Adams et al. 2010), which itself may be adaptive in certain circumstances (Smallwood and Schooler 2006). Future research integrating these literatures and associated methodologies is of critical importance. Much of the work in this section evaluates hypotheses drawn from previous literature, but there are also some novel findings. For example, Moruzzi, Rijsdijk, and Battaglia (2014, this issue) report that SCT, in contrast to inattention and hyperactivity, may be more influenced by non-shared environmental factors. To our knowledge, this is the first available evidence that SCT has an etiology that differs from ADHD. McBurnett et al. (2014, this issue) report that behaviors that resemble some aspects of working memory problems may be construed as a subfactor of SCT. This new finding is intriguing but highly preliminary and ripe for further study. Finally, the Lee et al. (2014, this issue) and the McBurnett et al. (2014, this issue) studies employed novel methods of measuring SCT. Other studies (Langberg et al. 2014, this issue; Willcutt et al. 2014, this issue) measured SCT using emerging measures that more adequately sample SCT than early studies that used only 2-4 items found in existing rating scales. However, the ample contributions made by other papers herein demonstrate that measures of SCT that are limited to the few items found on existing rating scales may still be of substantial value in exploiting archival data.
Conclusion Given the increasing interest in the study of SCT, and studies documenting its importance, it is an opportune time for a set of papers that together provide a review of SCT-related research conducted to date, address timely issues in the field, and point toward important research and clinical directions. Interestingly, DSM-5 was published as this Special Section was being prepared. In DSM-IV, SCT was to some extent included under the “Not Otherwise Specified” designation, whereby individuals who did not meet full criteria for ADHD but displayed inattention and “a behavioral pattern marked by sluggishness, daydreaming, and hypoactivity” could receive an ADHD
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NOS diagnosis. In DSM-5 , symptoms of SCT are no longer mentioned. In many regards, this is a welcome change, as increasing evidence (including multiple studies in this Special Section) provide support for SCT to no longer be subsumed under the umbrella of ADHD but rather to be considered as distinct from it. As such, there is a need for more studies that do not only examine SCT in ADHD-defined samples, particularly as SCT-related research extends to new disciplines and sub-disciplines (e.g., pediatric psychology; see Becker 2013) in an effort to further understand the causes, correlates, and consequences of SCT. On the other hand, the removal of any mention of SCT from DSM-5 may stall research (and, in turn, clinical practice), as most research conducted in psychology and psychiatry remains wedded to the use of DSM-defined categorical diagnoses. While we believe it is premature to consider SCT as a psychiatric disorder of its own, researchers should continue to investigate this possibility while also pursuing new and novel avenues of research. For example, although highly speculative at this point in time, it is interesting to consider whether SCT may be useful as a transdiagnostic construct as opposed to a disorder per se, much like emotion regulation is not itself a disorder but is nonetheless critically important for understanding psychopathology across the life span. These and many other directions for research are needed, and so we hope that this Special Section not only brings together papers to advance the current knowledge related to SCT but also spurs research in this exciting and expanding area of abnormal psychology.
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6 Lahey, B. B., Pelham, W. E., Schaughency, E. A., Atkins, M. S., Murphy, A., & Hynd, G. (1988). Dimensions and types of attention deficit disorder. Journal of the American Academy of Child and Adolescent Psychiatry, 27, 330–335. *Langberg, J. M., Becker, S. P., & Dvorsky, M. R. (2014). The association between sluggish cognitive tempo and academic functioning in youth with attention-deficit/hyperactivity disorder (ADHD). Journal of Abnormal Child Psychology. doi: 10.1007/s10802-0139722-3. Laufer, M., Denhoff, E., & Solomons, G. (1957). Hyperkinetic impulse disorder in children’s behavioral problems. Psychosomatic Medicine, 19, 38–49. *Lee, S., Burns, G. L., Snell, J., & McBurnett, K. (2014). Validity of the sluggish cognitive tempo symptom dimension in children: Sluggish cognitive tempo and ADHD-inattention as distinct symptom dimensions. Journal of Abnormal Child Psychology. doi: 10.1007/ s10802-013-9714-3. *Marshall, S. A., Evans, S. W., Eiraldi, R. B., Becker, S. P., & Power, T. J. (2014). Social and academic impairment in youth with ADHD, predominately inattentive type and sluggish cognitive tempo. Journal of Abnormal Child Psychology. doi: 10.1007/s10802-0139758-4. McBurnett, K., Pfiffner, L. J., & Frick, P. J. (2001). Symptom properties as a function of ADHD type: an argument for continued study of sluggish cognitive tempo. Journal of Abnormal Child Psychology, 29, 207–213. doi:10.1023/A:1010377530749. *McBurnett, K., Villodas, M., Burns, L. G., Hinshaw, S. P., Beaulieu, A., & Pfiffner, L. J. (2014). Structure and validity of sluggish cognitive tempo using an expanded item pool in children with attentiondeficit/hyperactivity disorder. Journal of Abnormal Child Psychology. Milich, R., Balentine, A. C., & Lynam, D. R. (2001). ADHD combined type and ADHD predominantly inattentive type are distinct and unrelated disorders. Clinical Psychology: Science and Practice, 8, 463–488. doi:10.1093/clipsy.8.4.463. *Moruzzi, S., Rijsdijk, F., & Battaglia, M. (2014). A twin study of the relationships among inattention, hyperactivity/ impulsivity and sluggish cognitive tempo problems. Journal
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Sluggish Cognitive Tempo in Abnormal Child Psychology: An Historical Overview and Introduction to the Special Section Stephen P. Becker & Stephen A. Marshall & Keith McBurnett
Published online: 24 November 2013 # Springer Science+Business Media New York 2013
Abstract There has recently been a resurgence of interest in Sluggish Cognitive Tempo (SCT) as an important construct in the field of abnormal child psychology. Characterized by drowsiness, daydreaming, lethargy, mental confusion, and slowed thinking/behavior, SCT has primarily been studied as a feature of Attention-Deficit/Hyperactivity Disorder (ADHD), and namely the predominately inattentive subtype/ presentation. Although SCT is strongly associated with ADHD inattention, research increasingly supports the possibility that SCT is distinct from ADHD or perhaps a different mental health condition altogether, with unique relations to child and adolescent psychosocial adjustment. This introductory article to the Special Section on SCT provides an historical overview of the SCT construct and briefly describes the contributions of the eight empirical papers included in the Special Section. Given the emerging importance of SCT for abnormal psychology and clinical science, there is a clear need for additional studies that examine (1) the measurement, structure, and multidimensional nature of SCT, (2) SCT as statistically distinct from not only ADHD-inattention but also other psychopathologies (particularly depression and anxiety),
S. P. Becker (*) Department of Psychology, Miami University, 90 North Patterson Avenue, Oxford, OH 45056, USA e-mail: [email protected] S. P. Becker Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA S. A. Marshall Department of Psychology, Ohio University, Athens, OH, USA K. McBurnett Department of Psychiatry, University of California, San Francisco, San Francisco, CA, USA
(3) genetic and environmental contributions to the development of SCT symptoms, and (4) functional impairments associated with SCT. This Special Section brings together papers to advance the current knowledge related to these issues as well as to spur research in this exciting and expanding area of abnormal psychology. Keywords ADHD . Attention deficit disorder . Attention-deficit/hyperactivity disorder . Comorbidity . Concentration deficit disorder . DSM-5 . History . SCT . Sluggish cognitive tempo Sluggish Cognitive Tempo (SCT) is characterized by behavioral symptoms such as drowsiness/sleepiness, seeming to be “in a fog,” daydreaming, mental confusion, slowness, physical hypoactivity/lethargy, and apathy. Given these descriptors, and as described in more detail below, it is not surprising that the study of SCT as a construct largely emerged from investigations of Attention Deficit Disorder (ADD), and, more recently, Attention-Deficit/Hyperactivity Disorder (ADHD). Given the clear association between SCT and ADHD, there has been ongoing and increasing interest in whether or not SCT is empirically distinct from dimensions of ADHD as defined by the fourth and fifth editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV and DSM-5 ; American Psychiatric Association [APA] 1994, 2013), as well as the degree to which SCT is itself associated with psychosocial functioning and impairment. Indeed, there has been a marked increase in the last dozen years in the number of studies examining SCT. In order to more clearly illustrate this rise of interest in the topic of SCT, a search of journal articles was conducted using PsycINFO, PubMed, and GoogleScholar databases. Articles that included “sluggish cognitive tempo” (or related terms such as “slow cognitive tempo”) in the title or abstract were identified, as
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were articles that did not mention SCT in the article title/ abstract but mentioned SCT (or related terms) elsewhere in the article. The number of articles identified in each of these two categories is displayed in Fig. 1. As shown, very few papers explicitly examined or even mentioned SCT between 1985 and 1999. Since 2000, however, there has been a clear and relatively steady increase in the number of studies that focus on SCT or mention SCT in the body of the paper. Many of the studies in this latter group make reference to SCT in the Discussion of the study findings, highlighting the growing awareness of, and interest in, SCT as an important area for research and clinical attention. It is within this context that the set of papers included in this Special Section were prepared. Before briefly reviewing the contributions included in the Special Section, we provide an historical overview of the study of the SCT construct.
An Historical Overview of SCT Conceptualizations of difficulties related to inattention, hyperactivity, and impulsivity have undergone several important changes, both before and after entering the psychiatric nomenclature as Hyperkinetic Reaction of Childhood in the DSM-II in 1968 (APA 1968). Although a detailed summary of the history of ADHD is beyond the scope of this article (see Barkley 2006, for a thorough review), the study of SCT is closely tied to the study of ADHD. Many early references to ADHD-like conditions in the literature, such as Heinrich Hoffman’s description of Fidgety Phil in 1865 (Stewart 1970) and George Still’s lectures in the Lancet in 1902 (Still 1902), emphasize overactivity and disinhibition as hallmark features of the disorder. However, even as early as 1798, a
Number of Articles
45 40
SCT in Article Text
35
SCT in Article Title and/or Abstract
30 25 20 15 10 5 0
Year of Publication
Fig. 1 Number of journal articles published in print or online between 1985 and 2012 that include sluggish cognitive tempo (SCT) in the article title/abstract (black fill) or the article body (diagonal line fill). Search was conducted using PsycINFO, PubMed, and GoogleScholar databases
medical textbook written by Alexander Crichton (Crichton 1798) described two forms of attentional deficits: one involving overarousal of attentional systems and the other involving underarousal and low levels of mental energy (see Palmer and Finger 2001). Study of this underactive form of inattention took a back seat to the study of children with observable hyperactivity and impulsivity (e.g., Laufer et al. 1957). However, work by Virginia Douglas in the 1970’s (e.g., Douglas 1972) stressed that inattention caused more impairment for these children than hyperactivity. Influenced by her work, the DSM-III (APA 1980) positioned inattention as the core symptom dimension under the diagnostic label of Attention Deficit Disorder (ADD; APA 1980). In addition, for the first time, the DSM-III allowed for the diagnosis of a subtype that presented without hyperactivity. This new subtype was formed primarily to encourage research on nonhyperactive presentations which, despite being observed clinically, had received little empirical attention (Milich et al. 2001). SCT took shape as a construct around this same time. Even as early as the 1960’s and 1970’s, individual SCT symptoms (e.g., daydreaming, drowsiness, lethargy, laziness in school) were included in broadband rating scales for children (e.g., Conners 1969; Peterson 1961; Quay and Quay 1965). However, whereas many studies indicated that inattention represented a separable dimension from hyperactivity (see Hinshaw 1987, for a review), SCT and other inattention items loaded together on a unidimensional inattention factor, such as the Attentional Problems-Immaturity subscale of the Revised Behavior Problem Checklist (RBPC; Quay and Quay 1965; Quay 1983) or the Inattentive-Passive subscale of the Conners Rating Scales (Conners 1969). Interestingly, the single inattention factor extracted from a wide item pool in a 1971 study by Dielman, Cattell, and Leeper was even labeled “Sluggishness” because it included SCT-like items (drowsiness, easily fatigued, easily confused, laziness in tasks, and passivity), yet, again, inattentive items (e.g., short attention span, inattentiveness to what other say, and distractibility) loaded with these SCT items. It was not until the mid-1980’s that empirical support for a SCT dimension separate from inattention emerged, led in large part by the work of Benjamin Lahey, Ph.D., and Caryn Carlson, Ph.D. (see Carlson 1986). Specifically, in a large, school-based sample, Neeper and Lahey (1986) replicated the often-found separation of inattention from hyperactivity; however, a factor labeled “Slow Tempo” also emerged that was comprised of sluggish, apathetic, lethargic, drowsy, and “in a world of his or her own” items. Soon after, Lahey et al. (1988) extracted a comparable sluggish tempo factor (with forgetful, sluggish, drowsy, and “difficulty following instructions” items) in a clinic sample, and found further that a three-factor model of hyperactivity–impulsivity, inattention– disorganization, and slow tempo provided the best-fitting model of ADD.
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It is important to note that this division of inattention into two dimensions also aligned with the division of ADD into two subtypes in the DSM-III during the same decade (APA, 1980). For instance, studies found that inattention subscales on commonly used rating scales such as the RBPC and the Child Behavior Checklist (CBCL; Achenbach and Edelbrock 1983) did not uniformly apply to both ADD subtypes. Children with ADD with hyperactivity (ADD/H) were uniquely elevated in attentional problems characterized by distractibility, sloppiness, carelessness, and irresponsibility items, whereas children with ADD without hyperactivity (ADD/noH) were uniquely elevated in attentional problems characterized by sluggishness, drowsiness, slowness, being “lost in a fog,” daydreaming, and apathy (Barkley et al. 1990; Lahey et al. 1985). Once factor analytic work had identified a distinct SCT factor, other studies found that SCT scores were uniquely elevated in children with ADD/noH as compared to children with ADD/H (Lahey et al. 1987, 1988). In an indirect fashion, the validity of SCT was supported by research showing that the two ADD subtypes were associated with a different pattern of external correlates. ADD/H was uniquely associated with higher levels of aggression, conduct problems, impulsivity, and peer rejection and lower levels of guilt, whereas ADD/noH was uniquely associated with higher levels of anxiety, unhappiness, shyness, and peer withdrawal and lower levels academic performance and math achievement (see Milich et al. 2001, for a review). Family psychiatric histories also differentiated the groups, as more ADD/H and substance abuse problems were reported in relatives of children with ADD/H and more anxiety and learning problems were reported in relatives of children with ADD/noH (Barkley et al. 1990). Although there were rarely differences between the two subtypes on neuropsychological tests (see Milich et al. 2001), some studies found that the ADD/H group exhibited greater problems with disinhibition (Barkley et al. 1991) whereas the ADD/noH group exhibited more problems with perceptual-motor speed, automatized processing, and inconsistent performance on a memory task (Barkley et al. 1990, 1991; Hynd et al. 1991). In 1987, the DSM-III-R eliminated the subtyping of ADD and instead created a single disorder named AttentionDeficit/Hyperactivity Disorder (ADHD; APA 1987). However, this decision to remove subtypes was short-lived, as the DSM-IV Work Group on Disorders Usually First Diagnosed in Infancy, Childhood, or Adolescence decided to revisit subtypes for the classification of ADHD. Influenced by the DSM-III ADD subtype validation research and SCT factor analytic work from the 1980’s, the DSM-IV work group considered incorporating SCT symptoms in the new diagnostic criteria for a reinstated nonhyperactive subtype of ADHD. The DSM-IV Options Book (APA 1991) proposed using two partially overlapping yet distinct sets of inattention symptoms to identify each of the subtypes: six overlapping symptoms
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(i.e., difficulty following instructions, difficulty sustaining attention, trouble listening, loses things, inattention to details, and disorganization), two symptoms unique to ADD/H (i.e., distractibility and shifts between uncompleted activities), and four SCT symptoms unique to ADD/noH (i.e., forgetfulness, daydreaminess, sluggishness/drowsiness, and apathy). Three of these SCT items–forgetfulness, daydreaminess, and sluggishness/drowsiness–were tested in the DSM-IV field trials. Although all three demonstrated strong positive predictive power (PPP), the daydreamy and sluggish/drowsy items showed poor negative predictive power (NPP), leading the work group to decide on a single, parsimonious list of inattention symptoms to be used for diagnosing both subtypes (Frick et al. 1994). Of the proposed SCT symptoms, only the forgetful item was included in the DSM-IV because it showed utility for both hyperactive and nonhyperactive subtypes (Frick et al. 1994). The exclusion of all but one SCT symptom from the DSM-IV ADHD criteria did not end interest in the construct. One reason for continued interest was that research examining the validity of DSM-IV subtypes was unconvincing (see Willcutt et al. 2012), and some thought that the DSM-IV diagnostic criteria for the new inattentive subtype (ADHD Predominantly Inattentive Type [ADHD-I]), which had been changed considerably from DSM-III criteria, identified too heterogeneous a group (McBurnett et al. 2001; Milich et al. 2001). Many cases with ADHD-I were found to have low levels of SCT, while a subset of others with ADHD-I showed high levels of SCT (Carlson and Mann 2002). Further, under DSM-IV criteria, individuals with up to 4 or 5 symptoms of hyperactivity-impulsivity could be diagnosed with ADHD-I, whereas many others diagnosed with ADHDI showed very few or no symptoms of hyperactivityimpulsivity (see Milich et al. 2001). This variability in ADHD-I was highlighted in a collection of commentaries in a 2001 issue of Clinical Psychology: Science and Practice , in which a number of ADHD experts argued that research into SCT could help specify an important dimension of attentional problems, as well as a distinct classification of attentional disorder (e.g., Milich et al. 2001). In conjunction with these commentaries, an empirical paper by McBurnett et al. (2001) replicated the factor analytic work of Lahey and colleagues from the 1980’s by extracting a similar SCT factor (forgetful, daydreams, sluggish/drowsy) in a large ADHD clinic sample. As illustrated in Fig. 1, this group of articles stimulated the growth in SCT research seen over the past dozen years. This growing body of research has focused on developing more comprehensive measures of SCT symptomatology and, in concert, using factor analysis to validate the internal and discriminant validity of the SCT construct. It is within this context of renewed interest in the measurement, validity, and correlates of SCT that this Special Section was prepared.
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Special Section Studies This Special Section includes eight empirical articles as well as a commentary by Russell Barkley, Ph.D. The empirical articles use an array of sample types and methodologies that together provide an important advance of the current literature. In the literature published up to this date, one of the most consistent findings regarding the internal validity of SCT is that it constitutes a latent factor that is separate from that of ADHD Inattention. Of the eight papers herein, four (Becker et al. 2014, this issue; Lee et al. 2014, this issue; McBurnett et al. 2014, this issue; Willcutt et al. 2014, this issue) evaluated internal consistency with various methods. All four replicated the general finding that SCT represents a distinct latent factor. Thus, this particular question—is there such a thing as SCT that is different from ADHD Inattention—seems to be laid to rest as of this issue of JACP because of the consistency with which a separate SCT factor is extracted across methods and data sets (note that recent studies also document SCT to be distinct from ADHD in adults; Barkley 2012; Becker et al. 2013). Another question in this literature is whether SCT is a different construct from internalizing problems in general, and from depression more specifically. Three of the papers (Becker et al. 2014, this issue; Lee et al. 2014, this issue; McBurnett et al. 2014, this issue) pose this question from different approaches. Overall, the findings suggest that SCT and internalizing disorder symptoms are indeed distinct, and that impairment correlated with SCT is not fully explained by the presence of internalizing symptoms. However, to complicate matters, some authors found that items indicating low activity, speed, or energy levels have the potential to confound SCT and depressive factors. It may be that behaviors related to sluggishness, a cardinal indicator of SCT, may in fact be a clinically observable feature of SCT, while at the same time such behaviors may not be helpful in measures of SCT when discriminant validity is the goal. SCT may be of little consequence if it can only be shown to be psychometrically distinct from ADHD and other psychopathologies but does not also predict meaningful external constructs. Nearly all of the papers in this Section, including those cited above as well as those from Langberg et al. (2014, this issue), Marshall et al. (2014, this issue), and Watabe et al. (2014, this issue) report on the external correlates of SCT. A key finding is that some first-order associations that do not seem to make sense—such as the positive associations of SCT with ADHD hyperactive-impulsive and oppositional defiant disorder (ODD) symptoms—seem to become nonexistent (or negative in direction) when other psychopathology dimensions such as ADHD inattention are also included in the model (Lee et al. 2014, this issue). Turning to impairment, the general finding of papers in this Special Section is that SCT adversely impacts some aspects of social and academic
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functioning, even when the contributions from ADHD symptoms are controlled. Watabe et al. (2014, this issue) provide the exception: depending on informant and context (school vs. home), SCT could appear adaptive or maladaptive. Future resolution of this conundrum might take into account the inverse association of SCT with ODD symptoms or behavioral dysregulation once other psychopathology symptoms are controlled (Becker et al. 2014, this issue; Lee et al. 2014, this issue), and the report from Weinberg and Brumback (1990) that children with Primary Disorder of Vigilance (a clinical syndrome with some resemblance to SCT) are unusually sweet and well-behaved. Likewise, it is possible that SCT represents a type of pathological mind wandering (Adams et al. 2010), which itself may be adaptive in certain circumstances (Smallwood and Schooler 2006). Future research integrating these literatures and associated methodologies is of critical importance. Much of the work in this section evaluates hypotheses drawn from previous literature, but there are also some novel findings. For example, Moruzzi, Rijsdijk, and Battaglia (2014, this issue) report that SCT, in contrast to inattention and hyperactivity, may be more influenced by non-shared environmental factors. To our knowledge, this is the first available evidence that SCT has an etiology that differs from ADHD. McBurnett et al. (2014, this issue) report that behaviors that resemble some aspects of working memory problems may be construed as a subfactor of SCT. This new finding is intriguing but highly preliminary and ripe for further study. Finally, the Lee et al. (2014, this issue) and the McBurnett et al. (2014, this issue) studies employed novel methods of measuring SCT. Other studies (Langberg et al. 2014, this issue; Willcutt et al. 2014, this issue) measured SCT using emerging measures that more adequately sample SCT than early studies that used only 2-4 items found in existing rating scales. However, the ample contributions made by other papers herein demonstrate that measures of SCT that are limited to the few items found on existing rating scales may still be of substantial value in exploiting archival data.
Conclusion Given the increasing interest in the study of SCT, and studies documenting its importance, it is an opportune time for a set of papers that together provide a review of SCT-related research conducted to date, address timely issues in the field, and point toward important research and clinical directions. Interestingly, DSM-5 was published as this Special Section was being prepared. In DSM-IV, SCT was to some extent included under the “Not Otherwise Specified” designation, whereby individuals who did not meet full criteria for ADHD but displayed inattention and “a behavioral pattern marked by sluggishness, daydreaming, and hypoactivity” could receive an ADHD
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NOS diagnosis. In DSM-5 , symptoms of SCT are no longer mentioned. In many regards, this is a welcome change, as increasing evidence (including multiple studies in this Special Section) provide support for SCT to no longer be subsumed under the umbrella of ADHD but rather to be considered as distinct from it. As such, there is a need for more studies that do not only examine SCT in ADHD-defined samples, particularly as SCT-related research extends to new disciplines and sub-disciplines (e.g., pediatric psychology; see Becker 2013) in an effort to further understand the causes, correlates, and consequences of SCT. On the other hand, the removal of any mention of SCT from DSM-5 may stall research (and, in turn, clinical practice), as most research conducted in psychology and psychiatry remains wedded to the use of DSM-defined categorical diagnoses. While we believe it is premature to consider SCT as a psychiatric disorder of its own, researchers should continue to investigate this possibility while also pursuing new and novel avenues of research. For example, although highly speculative at this point in time, it is interesting to consider whether SCT may be useful as a transdiagnostic construct as opposed to a disorder per se, much like emotion regulation is not itself a disorder but is nonetheless critically important for understanding psychopathology across the life span. These and many other directions for research are needed, and so we hope that this Special Section not only brings together papers to advance the current knowledge related to SCT but also spurs research in this exciting and expanding area of abnormal psychology.
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6 Lahey, B. B., Pelham, W. E., Schaughency, E. A., Atkins, M. S., Murphy, A., & Hynd, G. (1988). Dimensions and types of attention deficit disorder. Journal of the American Academy of Child and Adolescent Psychiatry, 27, 330–335. *Langberg, J. M., Becker, S. P., & Dvorsky, M. R. (2014). The association between sluggish cognitive tempo and academic functioning in youth with attention-deficit/hyperactivity disorder (ADHD). Journal of Abnormal Child Psychology. doi: 10.1007/s10802-0139722-3. Laufer, M., Denhoff, E., & Solomons, G. (1957). Hyperkinetic impulse disorder in children’s behavioral problems. Psychosomatic Medicine, 19, 38–49. *Lee, S., Burns, G. L., Snell, J., & McBurnett, K. (2014). Validity of the sluggish cognitive tempo symptom dimension in children: Sluggish cognitive tempo and ADHD-inattention as distinct symptom dimensions. Journal of Abnormal Child Psychology. doi: 10.1007/ s10802-013-9714-3. *Marshall, S. A., Evans, S. W., Eiraldi, R. B., Becker, S. P., & Power, T. J. (2014). Social and academic impairment in youth with ADHD, predominately inattentive type and sluggish cognitive tempo. Journal of Abnormal Child Psychology. doi: 10.1007/s10802-0139758-4. McBurnett, K., Pfiffner, L. J., & Frick, P. J. (2001). Symptom properties as a function of ADHD type: an argument for continued study of sluggish cognitive tempo. Journal of Abnormal Child Psychology, 29, 207–213. doi:10.1023/A:1010377530749. *McBurnett, K., Villodas, M., Burns, L. G., Hinshaw, S. P., Beaulieu, A., & Pfiffner, L. J. (2014). Structure and validity of sluggish cognitive tempo using an expanded item pool in children with attentiondeficit/hyperactivity disorder. Journal of Abnormal Child Psychology. Milich, R., Balentine, A. C., & Lynam, D. R. (2001). ADHD combined type and ADHD predominantly inattentive type are distinct and unrelated disorders. Clinical Psychology: Science and Practice, 8, 463–488. doi:10.1093/clipsy.8.4.463. *Moruzzi, S., Rijsdijk, F., & Battaglia, M. (2014). A twin study of the relationships among inattention, hyperactivity/ impulsivity and sluggish cognitive tempo problems. Journal
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