To appear in the P. McCardle, L. Freund, and J. a. Griffin (Eds.) Executive Function in Preschool Age Children: Integrating Measurement, Neurodevelopment and Translational Research, APA Press. Development of Selective Sustained Attention: The Role of Executive Functions Anna Fisher¹ and Heidi Kloos² ¹Carnegie Mellon University; ²University of Cincinnati Please address correspondence to: Anna Fisher, 335-I, Baker Hall, Department of Psychology, Carnegie Mellon University, Pittsburgh PA 15232, fidher49@andrew.cmu.edu Development of Selective Sustained Attention: Draft 1 Attention is a multi-faceted construct which notoriously lacks a commonly agreed upon definition. Nonetheless, there is a widespread agreement that attention is central to human performance. Several sub-functions of attention are commonly distinguished, including alerting (i.e., achieving high sensitivity to incoming stimuli), orienting (i.e., selecting information from sensory input), and executive (or endogenous) attention (i.e., monitoring/resolving cognitive conflict and directing cognitive resources on a volitional basis) (Colombo & Cheatham, 2006; Posner & Petersen, 1990; Posner & Rothbart, 2007). Some theories of attention also include maintenance (i.e., sustaining attention) as a separate sub-function (Kahneman 1973), although others consider it as a part of the alerting function (Posner & Peterson, 1990; Posner & Rothbart, 2007) or the executive function (Colombo & Cheatham, 2006). The focus of this chapter is the type of attention that is both selective (as opposed to divided over multiple tasks) and sustained (i.e., extended over time as opposed to extremely brief, as in visual search which can typically be accomplished in several hundred milliseconds). Selective sustained attention, which has also been referred to as focused attention in the infancy literature (e.g., Colombo & Cheatham, 2006; Oakes, Kannass, & Shaddy, 2002; Ruff & Rothbart, 2001; Tellinghuisen, Oakes, & Tjebkes, 1999), is the ability to maintain focus on a single object, task, or sensory channel for an extended period of time. It is a crucially important ability that has been implicated in learning across development – from the crib to the classroom and beyond (e.g., Kupietz & Richardson, 1978; Oakes, Kannass, & Shaddy, 2002). As Oakes et al. (2002) put it), “if attention were constantly reoriented to every new event, it would be difficult … to learn about any single object or event” (p.1644). This chapter reviews extant 1 Development of Selective Sustained Attention: Draft 1 research on the development of selective sustained attention and discusses research opportunities in furthering our understanding of this important ability. Theoretical Perspectives on Selective Sustained Attention Ruff and Rothbart (2001) proposed that selective sustained attention is subserved by two systems that are anatomically and neurally separate: the orienting system and the executive control system. These two systems are said to have different maturation schedules, with the orienting system maturing during infancy and the executive control system following a protracted maturational schedule that extends into adolescence (Diamond, 2002; Luna, 2009; Posner & Rothbart, 2007). Therefore, the orienting system is assumed to subserve selective sustained attention early in life, whereas the executive control system becomes increasingly important later in development. 2.1. Two-Systems Theory of Selective Sustained Attention Orienting in infants is often characterized as stimulus-driven or automatic (i.e., driven by exogenous factors), rather than participant-driven or voluntary (i.e., driven by endogenous factors). That is to say, the locus of attention in newborns and young infants is determined largely by the properties of the stimulus, such as its frequency and duration for auditory stimuli, and intensity, degree of curvature, and brightness for visual stimuli (Bornstein, 1990; Ruff & Rothbart, 2001). This lack of intentionally guided attention is furthermore illustrated by the phenomenon called obligatory looking: Once a visual stimulus “grabs” attention, 1- to 2-monthold infants often find it difficult to disengage attention, and unlimited exposure to attentiongrabbing stimuli may result in prolonged looking ending in considerable distress (Colombo, 2001; Stechler & Latz, 1966). Obligatory looking diminishes after 2 months of age suggesting development of some degree of control over disengagement of attention. Similarly, control over 2 Development of Selective Sustained Attention: Draft 1 engagement of attention also develops during the first months of life. For example, unlike 4month-old infants, 6-month-olds are capable of both reactionary saccades (saccades in response to the appearing target) and anticipatory saccades (saccades to the anticipated location of a yet invisible target) (Johnson, Amso, & Slemmer, 2003). According to Ruff & Rothbart (2001), periods of selective sustained attention in early infancy are “a prolongation of the orienting response, sustained as long as the object retains some novelty” (p.114). Consequently, early in life sustained attention is at its maximum when objects are novel; termination of sustained attention is particularly likely if there is competition from another novel object or event (Richards, 1988). There is a general agreement in the literature that between 9 and 12 months of age many cognitive processes, including selective sustained attention, gradually come “under control of both systems rather than one” (Ruff & Rothbart, 2001, p.117; see also Colombo & Cheatham, 2006; Diamond, 2006; Oakes et al., 2002). There is also agreement that the ability to sustain attention in a voluntary fashion is supported by higher-order cognitive functions that are typically characterized as executive functions, namely inhibition and working memory. It has been argued that sustaining attention to an object or a task requires inhibition of orienting to irrelevant objects and events (Colombo & Cheatham, 2006; Kane & Engle, 2002; Ruff & Rothbart, 2001). Inhibition is traditionally considered one of the core executive functions (e.g., Miyake et al., 2000; although see MacLeod, Dodd, Sheard, Wilson, & Bibi, 2003 for divergent arguments), and persistent correlations between level of inhibitory control and sustained attention have been documented in children as well as adults (Barkley, 1997; Hrabok, Kerns, & Müller, 2007; Reck & Hund, 2011). 3 Development of Selective Sustained Attention: Draft 1 Working memory, another of the core of executive functions, is also considered to be a key component in the ability to voluntarily sustain attention (Colombo & Cheatham, 2006; Kane & Engle, 2002): one needs to maintain an active representation of a goal in order to organize behavior to achieve this goal. However, Colombo & Cheatham (2006) also argued that the linkages between selective sustained attention and memory are bi-directional, as memory “can serve as a basis for the distribution of attentional resources” and “sustained allocation of attention to a stimulus allows for the establishment of an enduring memory trace” (p. 300). Neural Bases of the Two Systems of Attention Functional neuroimaging data provide support to the proposal that the orienting and executive systems of attention involve distinct anatomical regions and chemical modulators (Colombo & Cheatham, 2006; Fan, McCandliss, Fossella, Flombaum, & Posner, 2005; Posner & Rothbart, 2007). In humans, brain injury to posterior parietal lobe, superior colliculus, or lateral pulvinar nucleus of the thalamus impairs the ability to shift attention covertly (i.e., in the absence of shifting one’s eyes; Posner & Peterson, 1990). However, injury to these brain regions impairs orienting in different ways. Specifically, damage to the posterior parietal lobe produces the greatest impairment in the ability to disengage attention from target stimuli contralateral to the side of the lesion. In contrast, progressive deterioration in the superior colliculus leads to a deficit in the ability to shift attention, regardless of whether attention was first engaged elsewhere or not. Yet a different pattern is found in patients with lesions of the thalamus, who exhibit difficulties in engaging attention to a target stimuli contralateral to the side of the lesion (Posner & Peterson, 1990). The executive control system is traditionally associated with prefrontal cortex (PFC) and anterior cingulate gyrus (e.g., Diamond, 2002; Miller & Cohen, 2001; Posner & Rothbart, 2007). 4 Development of Selective Sustained Attention: Draft 1 PFC damage has long been known to produce profound deficits in goal-directed behavior. Patients with prefrontal damage exhibit difficulties in classic tasks assessing executive functioning, such as Stroop, Wisconsin Card Sorting Task, and Tower of London (Miller & Cohen, 2011). With regards to its maturation, PFC is said to undergo “one of the longest periods of development of any brain region, taking over two decades to reach full maturity” (Diamond, 2002, p. 466). Evidence for protracted maturation of the PFC comes from the postmortem studies of myelination, examination of resting levels of glucose metabolism, and studies of synaptogenesis and gray matter reduction (for review see Casey, Giedd, & Thomas, 2000). Studies of chemical modulation of attention networks are often carried out on alert animals which can perform a variety of attention tasks after being injected with various neuromodulators. Chemical modulation in the brain regions associated with the orienting network has been linked to the neurotransmitter acetylcholine (for review see Davidson & Marrocco, 2000). For example, blocking cholinergic receptors with scopolamine, an anticholinergic drug, impairs orienting and sustained attention in rhesus monkeys and rats (Callahan, Kinsora, Harbaugh, Reeder, & Davis, 1993; Jones & Higgins, 1995). Similarly, reduction in cholinergic neurotransmission through selective lesions in monkeys and rats leads to impaired orienting but not learning or working memory (Chiba, Bushnell, Oshiro, & Gallagher, 1999; Voytko et al., 1994). Finally, direct injections of scopolamine into the lateral intra-parietal area of rhesus monkeys have been shown to produce dose-dependent increases in reaction times and decreases in accuracy during visual orienting tasks (Davidson & Marrocco, 2000). In contrast, chemical modulation in the prefrontal cortex is linked to the neurotransmitter dopamine. For example, local injections of selective dopamine antagonists into the prefrontal cortex in rhesus monkeys led to dose-dependent increases of error rates and reaction time on 5 Development of Selective Sustained Attention: Draft 1 working memory tasks but not on control tasks (Sawaguchi & Goldman-Rakic, 1991); similar findings have been obtained in rats (Seamans, Floresco, & Phillips, 1998). Furthermore, when infant rhesus monkeys show improvement in performance on several tasks thought to involve prefrontal cortex, there is also a concomitant increase in the level of dopamine and density of dopamine receptors in their prefrontal cortex (for a review see Diamond, 2002). In human infants, reduced dopamine level in prefrontal cortex is associated with reduced level of performance on tasks requiring working memory and response inhibition (Diamond, Briand, Fosella, & Gehlbach, 2004; Diamond, Prevor, Callender, & Druin, 1997). Finally, several recent neuroimaging and genetic studies have established linkages between specific genes, neurotransmitters, and attention networks (for review see Posner & Rothbart, 2007). Many genes exhibit variants, or polymorphisms, which are relatively high in frequency. These polymorphisms are thought to lead to different efficiency of cholinergic and dopaminergic modulation, and in turn to individual differences in performance on attention tasks. Several studies have linked specific genes and gene polymorphisms to modulation of orienting through acetylcholine, and executive control through dopamine (Diamond et al., 2004; Parasuraman, Greenwood, Kumar, & Fossella, 2005). Summary Overall, selective sustained attention is commonly thought to be subserved by two distinct systems of attention, the orienting system and the executive system. Neuroimaging and neurophysiological studies suggest that these systems involve distinct anatomical regions and different maturation schedules. Specifically, the executive system (subserved by the prefrontal cortex and anterior cingulate gyrus) is thought to follow a more protracted maturational schedule than the orienting system (subserved by the posterior parietal lobe, superior colliculus, and 6 Development of Selective Sustained Attention: Draft 1 lateral pulvinar nucleus of the thalamus). Neuroimaging and genetic studies indicate that these two systems also involve distinct chemical modulators, with the executive system being linked to dopamine and the orienting system to acetylcholine. Selective Sustained Attention across the Lifespan Characterizing selective sustained attention at different points in development often involves drastically different research paradigms. Therefore, this part of the chapter is organized around different types of measures that have been used to study selective sustained attention from infancy to adulthood. Looking-Based Measurement of Selective Sustained Attention This section summarizes research on selective sustained attention that is based on, or involves to a large degree, measures of looking behavior. Looking has been traditionally used to investigate different aspects of visual attention across the lifespan (for reviews see Colombo, 2001; Henderson & Ferreira, 2004; Just & Carpenter, 1976), and there is evidence that visual attention and saccadic eye movements rely on the same neural mechanisms (Corbetta et al., 1998). Furthermore, looking is sometimes used as a behavioral measure of auditory attention as well (e.g., Reisberg, 1978; Saffran, Newport, & Aslin, 1996; Spelke, 1976). Ample evidence suggests that selective sustained attention is present in young infants, including newborns. For example, when newborns (averaging less than 40 minutes after birth at the moment of testing) are presented with moving schematic face-like images and scrambled images (containing the same features as the face-like stimuli), newborns turn their head and eyes to track both kinds of stimuli, although more so for the face-like images (Goren, Sarty, & Wu, 1975; Johnson, Dziurawiec, Ellis, & Morton, 1991). The findings resulting from this paradigm are usually presented in terms of degree of head and eye rotation rather than duration of visual 7 Development of Selective Sustained Attention: Draft 1 attention; however, based on the reported results it is possible to estimate that newborns can sustain attention to face-like stimuli for up to 9 seconds (mean reported eye rotation was approximately 45° and stimuli were moved at 5° per second; Johnson et al., 1991). Measuring infants’ looking and heart rate, Richards and colleagues (e.g., Richards, 1987; Richards & Casey, 1988) identified different attentional states in 2- to 6-month-old infants including: pre-attention, orienting, sustained attention, and attention termination. In this paradigm, animated stimuli (e.g., a Sesame Street recording or a series of sequentially appearing and disappearing concentric squares) were presented to infants on a TV monitor. Results indicated that rapid heart-rate deceleration accompanied initial orienting to a stimulus; slower heart rate was maintained throughout the sustained attention phase and heart rate returned to baseline level when attention was terminated (for a review see Richards, 2003). Such changes in heart rate show that selective sustained attention to dynamic events in 2- to 6-month-old infants can last from 2 up to 120 seconds, with duration of sustained attention influenced by the state of an infant during testing, stimulus novelty and complexity, as well as individual differences. With regard to static two-dimensional images, a steady age-related decrease in looking duration was found during the first 6 months of life (Colombo & Cheatham, 2006). This decrease is traditionally attributed to improved efficiency of processing with development: the more efficiently an infant can encode the features of an object or event, the shorter looking duration is required to do so. This possibility is supported by negative correlations between duration of looking early in the first year of life and later cognitive outcomes (i.e., IQ and language development) (for a review see Bornstein, 1990). However, it has also been shown that between approximately six months and three years of age duration of looking to static images steadily increases (Colombo & Cheatham, 2006). 8 Development of Selective Sustained Attention: Draft 1 Furthermore, beyond age one, the correlations between looking duration and cognitive outcomes are positive, such that longer looking predicts better learning (Dixon & Salley, 2007), problem solving (Kannass & Colombo, 2007), and better cognitive outcomes later in development (Lawson & Ruff, 2004). Colombo and Cheatham (2006) suggest that nonlinear changes in looking duration during infancy provide support for the hypothesized shift in the locus of attentional control. In particular, they suggest that the U-shaped curve of looking duration in infancy stems from a change in the processes underlying selective sustained attention – from reflexive/endogenous to voluntary/exogenous. According to this proposal, while initial decrease in looking duration over the first six months of life likely reflects improved encoding efficiency, the increase in looking duration over the next 3 years likely reflects “the ability to voluntarily sustain or maintain attention to an object, either in response to the object’s properties or to some short-term goal” (Colombo & Cheatham, 2006, p. 294). There has also been reported a developmental increase in duration of looking at a blank screen in anticipation of a rewarding stimulus. Goldman, Shapiro, and Nelson (2004) developed a computerized measure of sustained attention for toddlers and young children - the Early Childhood Vigilance Task (ECVT). In this task children need to look at a computer screen in the absence of stimuli in order to view interesting stimuli (e.g., moving cartoon characters) when they appear: the better children are able to sustain attention to the blank screen in 5- to 15-second intervals between cartoons, the more likely children are to view the short cartoons when they appear on the screen. Children are videotaped during the task and their looking is later analyzed to determine the total duration of time children spent looking toward the computer screen. With a 9 Development of Selective Sustained Attention: Draft 1 sample of 12- to 46-month-old children, Goldman et al. (2004) found a significant age-related increase in total looking towards the screen on the ECVT. Play-Based Measurement of Selective Sustained Attention Developmental studies of selective sustained attention often use elaborate coding schemes to determine the attentional state of a participant, typically during free play. The coding schemes commonly distinguish between selective sustained (or focused) attention and casual attention. Selective sustained attention is measured by coding a child’s direction of gaze and behavior, including facial expressions that are intent or show concentration or interest (knitted brows, lip biting), body movement changes such as minimal extraneous movement, postural enclosure of the object, or leaning toward while gazing at the object (Choudhury & Gorman, 2000; Oakes, at al., 2002; Ruff & Capozzoli, 2003; Ruff & Rothbart, 2001; Tellinghuisen, Oakes, & Tjebkes, 1999). Studies that utilized coding schemes similar to the one described above point to a steady increase in duration of selective sustained attention, from approximately 2 minutes in 21-month-old infants to 4 minutes in 2- and 3-year-old children, and to over 9 minutes in 5- and 6-year-olds (Choudhury& Gorman, 2000; Ruff & Lawson, 1990; Sarid & Breznitz, 1997). Being in the state of selective sustained attention has been shown to affect children’s response to environmental distracters. For example, following an episode of distraction children are more likely to return to the interrupted activity if they were in a state of selective sustained attention than in the state of casual attention (Oakes & Tellinghuisen, 1994). Furthermore, infants and children take longer to orient to environmental distracters when in the state of selective sustained attention (Lansink & Richards, 1997; Oakes et al., 2002; Oakes & Tellinghuisen, 1994). For example, Oakes et al. (2002) presented 6- to 9-month-old infants with 10 Development of Selective Sustained Attention: Draft 1 target events that consisted of colorful multipart toys. As infants investigated the toy, distracter events were presented in the periphery on a computer monitor. Distracters consisted of visualauditory compounds (i.e., colored blinking rectangles accompanied by a beeping sound) and were presented until infants visually fixated them. Latencies to orient to a distracter were longer when infants were in a state of selective sustained attention and target events were novel. Similarly, Richards (1987) showed that latency to orient to a distracter is greater if the distracter is presented during the maximum heart rate deceleration (i.e., the sustained attention phase to the target stimulus) compared to distracter presentation during heart rate acceleration (i.e., return to baseline which marks termination of selective sustained attention). Performance-Based Measurement of Selective Sustained Attention Beyond infancy and toddlerhood, one of the most widely used tests of selective sustained attention is the Continuous Performance Test (CPT; Rosvold, Mirsky, Sarason, Bransome, & Beck, 19561). The CPT was originally developed as a screening tool for brain damage, but is widely used today in research on sustained attention. This includes attention in neurotypical adults (e.g., Davies and Parasuraman, 1982; Nuechterlein, Parasuraman, & Jiang, 1983), attention in typically developing children (e.g., Akshoomoff, 2002; Corkum, Byrne, & Ellsworth, 1995), and attention in patients with attention deficit hyperactivity disorder (ADHD) (e.g., Barkley, 1990; Kerns & Rondeau, 1998) and schizophrenia (e.g., Cornblatt & Keilp, 1992; Nuechterlein & Dawson, 1984). The core feature of the CPT is that participants are presented with a continuous stream of stimuli (visual or auditory) consisting of infrequently appearing targets and frequently appearing Several commercial versions of this task have been developed (e.g., Conners’ CPT: Conners, 2002; Gordon Diagnostic System: Gordon, 1983; Test of Variables of Attention: Greenberg & Waldman, 1993). Note however, that there are many versions and modifications of the CPT, with some versions being referred to by other names (e.g., “Picture Selection Task”, Akshoomoff, 2002). 1 11 Development of Selective Sustained Attention: Draft 1 non-targets (usually numbers or letters). The typical duration ranges from 5 to 40 minutes (with shorter durations usually used with younger participants). Participants have to respond to targets (usually via a button press) and withhold responses to non-target stimuli. Originally performance on the CPT was measured in terms of commission errors (false alarms), omission errors (misses), and reaction time; however, signal detection indices d' (sensitivity) and β (response criterion) have become increasingly popular (Davies & Parasuraman, 1981). A variety of factors were found to affect performance on the CPT (for extensive reviews see Ballard, 1996; Riccio, Reynolds, & Lowe, 2001). Depending on the version of the test, they include (1) the ratio of targets to non-targets, (2) the presentation rate, (3) the type of target event (e.g., target event can be defined as letter “X” in the X-CPT version or as letter “X” preceded by a different letter, for instance “A”, in the AX-CPT version); (4) the modality in which the task is administered (i.e., visual vs. auditory); (5) demographics (primarily age, although some effects of education level and gender have been observed; Chen, Hsiao, Hsiao, & Hwu, 1998); (6) whether clinical symptoms are present (i.e., the diagnosis of ADHD, schizophrenia, and more recently Specific Language Impairment; Spaulding, Plante, & Vance, 2008); (6) environmental factors (e.g., noise and temperature); and (7) the person’s physiological state (e.g., amount of sleep; intake of caffeine, glucose, alcohol, or medication). Summarizing these effects is beyond the scope of this chapter, particularly given the many different versions of the CPT; instead we will concentrate on the typical patterns of performance in neurotypical populations. The core CPT pattern with adults is a decrease in performance over time, usually referred to as vigilance decrement. Vigilance decrement in CPT typically occurs for relatively long task durations; however, under certain conditions (e.g., detection of perceptually degraded stimuli), decrements in performance can occur after less than 10 minutes of performing the task 12 Development of Selective Sustained Attention: Draft 1 (Nuechterlein et al., 1983). Standard versions of the CPT have been successfully used with children starting from approximately 5 to 6 years of age (e.g., Edley & Knopf, 1987; Gordon, Thomason, & Copper, 1990). However, the task was deemed inappropriate for younger children, primarily because of long task durations and possible unfamiliarity with letters and numbers. Corkum et al. (1995) created the first adaptation of the CPT that closely paralleled the adult versions. In their version, letters and numbers were substituted for pictures of familiar objects (e.g., ice-cream, sun, pig, lollipop), task duration was reduced to 9 minutes, rate of presentation of stimuli was decreased to allow for longer viewing time and a longer response window, and a training phase was included to familiarize children with the task. Despite these changes, 50% of 3-year-olds failed to complete the task. Performance of the 3-year-old children who completed the task was significantly below that of 4- and 5-year-olds in terms of both misses and false alarms; additionally, younger children spent more time looking away from the computer screen during the task than did older children. Importantly, vigilance decrement was observed in all three age groups for omission errors, with the slope of the decrement being steeper for younger children. Based on the results reported by Corkum et al. (1995), successive studies using the CPT with preschool-age children further reduced the task duration to 5 minutes (Akshoomoff, 2002; Kerns & Rondeau, 1998). With the reduced task duration, almost all children were able to complete the task, although Akshoomoff (2002) found that nearly half of the children below 4.5 years of age did not reach the performance criterion for inclusion in data analyses (i.e., at least 50% hits and less than 20% false alarms). Overall, developmental studies indicate a clear agerelated improvement in CPT performance from preschool age until adolescence (Akshoomoff, 13 Development of Selective Sustained Attention: Draft 1 2002; Annett, Bender, & Gordon, 2007; Corkum et al., 1995; Cornblutt et al., 1988; Kerns & Rondeau, 1998) and decreased performance with aging (e.g., Chen et al., 1998). Summary In infancy, development of selective sustained attention follows a U-shaped pattern, characterized by initial decrease in looking duration at static images until approximately 6 months of age, and subsequent increase in looking over the next three years. Beyond the first year of life, all paradigms used to investigate selective sustained attention (i.e., looking-based, play-based, and performance-based paradigms) indicate improvement in this ability from infancy to adulthood, with marked gains during the preschool years. Performance-based measures also indicate a decline in selective sustained attention in the course of aging. Opportunities for Research Despite much progress made in the study of development of selective sustained attention, important issues remain to be addressed, including clarifying several conceptual issues and advancing the methodological toolbox. Addressing these two issues will ultimately allow us to specify more precisely the coordination of the two systems supporting selective sustained attention at different points in development. Conceptual Issues in the Study of Selective Sustained Attention Whenever multiple tasks are used to assess purportedly the same psychological process, it is important to understand whether these different tasks tap into the same process. With regards to selective sustained attention, there are at least two important differences between the paradigms used with younger and older participants. The first critical difference is that lookingbased and play-based measures are self-paced and allow children to stay on task until they lose interest, whereas predetermined task durations are used in the CPT. It is possible that this 14 Development of Selective Sustained Attention: Draft 1 difference taps into the distinction between controlled and automatic processes: looking- and play-based measures may be well suited to assess selective attention sustained in an automatic stimulus-driven fashion and CPT may be well suited to assess selective attention sustained in a controlled fashion. However, caution is needed when adopting this interpretation of task differences. Specifically, while infants indeed sustain attention to an object or activity for as long as it maintains some level of novelty, research reviewed earlier in this chapter indicates that toddlers and preschoolers clearly have some degree of control over how their attention is allocated and maintained. Therefore, as Ruff & Rothbart (2001) pointed out, the differences uncovered by different paradigms may stem not only from the differences in the locus of control of attention, but also from the differences in the degree to which the task is motivating to participants of different ages. One could argue that executive control is needed precisely when the task/activity is not intrinsically motivating but needs to be performed nonetheless. This, however, poses a new problem, because executive control is often defined as “the ability to orchestrate thought and action in accordance with internal goals” (Miller & Cohen, 2001, p. 167). Intrinsic motivation is by definition driven by the participants’ intentions (although it can interact with the properties of the outside world). Clearly, further research is needed to clarify the relationship among selective sustained attention, motivation, and executive control. The second important difference is that in looking/play-based measures of selective sustained attention participants actively engage in an activity when the measurement is taken, whereas in the CPT participants spend a significant proportion of the time in preparation for action – often referred to as vigilance. Therefore, it is not at all clear whether the two kinds of paradigms measure the same kind of process. Both sustained attention and vigilance refer to attentional processes unfolding over time. However, unlike vigilance, which involves 15 Development of Selective Sustained Attention: Draft 1 maintaining alert state, sustained attention refers to active engagement with a particular activity for a period of time. Traditionally, the vast majority of researchers use the term sustained attention interchangeably with the term vigilance. This is problematic if the two processes are distinct, and this possibility has been recently raised by Egeland and Kovalik-Gran (2010). In a recent study, these researchers examined the factor structure of the commercial Conner’s CPT (Conners, 2002) in a clinical sample of participants with compromised sub-functions of attention. The scores loaded onto five different factors, identified as focusing, hyperactivity–impulsivity, sustained attention, mental control, and vigilance. Egeland and Kovalik-Gran (2010) concluded that the CPT assesses “not only sustained attention, as we are accustomed to think, but also other aspects of attention” (p. 343). With regard to the distinction between vigilance and sustained attention, Egeland & Kovalik-Gran summarized it as a “differentiation between a fall in vigilance when driving on monotonous straight roads as opposed to fatigue because of a high activity level over time”. Measurement Issues in the Study of Selective Sustained Attention As stated above, the CPT is by far the most common measure of selective sustained attention from preschoolage onward. Originally this task has been considered a relatively “pure” measure of selective sustained attention (Ballard, 1996). However, subsequent research highlighted that it is not clear to what degree the CPT measures selective sustained attention versus other aspects of performance. For example, there is a consistent relationship between CPT performance and academic readiness (Edley & Knopf, 1987), classroom inattentiveness (Kupietz & Richardson, 1978), and academic performance (Annett et al., 2007; Riccio, Reynolds, Lowe, & Moore, 2001). At the same time, CPT performance is correlated not only with academic success but also with general tests of intelligence, memory, and speed of processing (Annett et 16 Development of Selective Sustained Attention: Draft 1 al., 2007; Gordon et al., 1990; Riccio, et al., 2001). All of these factors are also known to correlate with academic achievement; thus it is not clear what proportion of the variance in academic achievement is uniquely accounted for by CPT performance. More importantly, it is not clear to what extent general intelligence, memory, and speed of processing are reflected in CPT performance. Shalev, Ben-Simon, Mevorach, Cohen, & Tsal (2011) recently evaluated a new version of the CPT that is intended to minimize memory and perceptual components of the task. The results of this evaluation are promising; however, further evaluations are clearly needed, particularly with children and clinical populations. Tapping multiple aspects of performance is not unique to the CPT: many cognitive measurement tools, particularly those designed to study higher-order processes, tap more than one aspect of performance – an issue to which Miyake et al. (2000) referred as the “task impurity problem.” Miyake and colleagues offered the following solution to this problem in their research on the structure of executive functions: “We … carefully select multiple tasks that tap each target executive function, and examine the extent of unity or diversity of these three executive functions at the level of latent variables (i.e., what is shared among the multiple exemplar tasks for each executive function), rather than at the level of manifest variables (i.e., individual tasks)” (p. 54). Implementation of this elegant solution to the task impurity problem indicated that set shifting, information monitoring, and inhibition are separable but related functions. Notice that attention maintenance was not included in Miake et al.’s (2000) study, as it was not included in the majority of other similar analyses of the unity and diversity of executive functions (for a review see Garon, Bryson, & Smith, 2008). One reason for this omission could be that attention maintenance is not under the purview of executive control, although several theoretical proposals suggest otherwise (Colombo & Cheatham, 2006; Ruff & Rothbart, 2001). 17 Development of Selective Sustained Attention: Draft 1 Another reason could be relative paucity of tools for assessing selective sustained attention, which would make the central feature of Miake et al.’s approach (i.e., selection of multiple tasks that putatively tap the same construct) impossible. Given the suggested task impurity problem with regards to the CPT, an important direction for future research in this area is development of new measurement tools, particularly tools that are not based on the CPT paradigm. In the next section we briefly describe our research on developing a new developmentally-sensitive paradigm – the Object Tracking task – for assessment of selective sustained attention in the visual domain. The Object Tracking Task and Associated Findings In the Object Tracking task participants visually track a target moving among several distracters. All objects move along a random trajectory on a grid and participants are asked to report the last location visited by the target object before it disappears; in the studies briefly described below each location was marked by a different cartoon character to facilitate reporting. Targets and distracters are randomly selected on each trial from a pool of unique objects (e.g., a red circle, a green diamond) At the onset of each trial the target is clearly marked by being encircled in red (see Figure 1; the circle disappears when the objects start moving). At the end of each trial participants are asked to identify the target object. This memory check helps to discriminate between two possible reasons why a participant may fail to correctly report the location where the target object disappears. The first possibility is that a child may fail to actively maintain the representation of the specific object to be tracked; this would indicate working memory failure. The second possibility is that a child may track distracters for a part of the trial despite remembering which object was supposed to be watched; this would indicate the failure of selective sustained attention. 18 Development of Selective Sustained Attention: Draft 1 Empirical results based on the Object Tracking paradigm are partially described in Fisher (2010) and we will only briefly summarize them here. Three- to 5-year-old children were presented with the task, with trial duration set at 10 seconds. There were two experimental conditions. In the Homogeneous Distracters condition there were two distracters which were identical to each other and different from the target; in the Heterogeneous Distracters condition, the two distracters were different from each other and from the target (see Figure 1). The target objects were expected to be more distinct, and thus more salient, in the Homogeneous Distracters condition. All children were presented with these conditions in counterbalanced order. We predicted that performance in the Heterogeneous Distracters condition should reflect the contribution of predominantly endogenous factors, as children were engaged in a task that was not intrinsically motivating and the task provided no contextual support that could benefit performance (i.e., target objects were not more salient than distracters). In the Homogeneous Distracters condition each target object was unique and likely more salient than distracters. Thus, performance in this condition was expected to reflect the contributions of both endogenous factors (e.g., completing a task that is not intrinsically motivating) and exogenous factors (e.g., higher saliency of target objects compared to distracters). The difference in performance between these conditions was expected to reflect the unique contribution of exogenous factors to performance on this task at different points in development. It is important to note that manipulating saliency of the target objects within the same paradigm allowed us to addresses the concern raised by Ruff & Rothbart (2001) regarding the interpretation of findings as reflecting exogenous or endogenous locus of attentional control. Specifically, any differences in performance observed between conditions could not be due to greater motivation to perform one task vs. another, as all children performed the same task. 19 Development of Selective Sustained Attention: Draft 1 Differences in tracking performance could arise from differences in memory demands, but memory performance was equivalent in both conditions (Figure 2): memory accuracy was lower in 3-year-olds than in both older age groups. However there were no differences in memory performance between the Homogeneous and Heterogeneous Distracters conditions in any age group. Furthermore, memory performance was equivalent in 4- and 5-year-old children. Despite equivalent memory performance, there were substantial differences in tracking accuracy in the two experimental conditions in younger children, with greater accuracy in the Homogeneous than Heterogeneous Distracters condition (Figure 2). Follow-up experiments indicate that some parametric manipulations (e.g., removing background images) decrease task difficulty and thus make it possible to extend the task to younger children, and other parametric manipulations (e.g., increasing the number of distracters and the grid size) increase the task difficulty, and thus make it possible to extend the task to older children. Test-retest reliability of this task has been relatively high in our initial testing (r = .80). Overall, our research indicates that the Object Tracking task is developmentally sensitive, has good parametric properties, allows dissociating memory failures from attention failures, and makes it possible to estimate the contribution of exogenous and endogenous factors to maintaining selective attention within the same paradigm. While these initial results are promising, clearly further research is needed to evaluate this new paradigm as well as develop other paradigms for investigating selective sustained attention and its underlying mechanisms. Conclusions Selective sustained attention is an important cognitive process, implicated in both successful learning and performance. Several theoretical accounts suggest that in early infancy sustaining selective attention is subserved by the orienting system, and beyond infancy by the 20 Development of Selective Sustained Attention: Draft 1 executive control system. Ample empirical evidence has been accumulated to support the role of the orienting system in selective sustained attention; however, there is less direct evidence for the role of the executive control system and very little is known about the coordination of these two systems in the course of development. Lastly, several conceptual issues and measurement issues in the study of selective sustained attention remain to be addressed in future research. 21 Development of Selective Sustained Attention: Draft 1 Acknowledgements Preparation of this chapter was supported in part by grant number 1R03HD060086-01A1 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development to Anna Fisher and by grant number NSF DRL #723638 from the National Science Foundation to Heidi Kloos. 22 Development of Selective Sustained Attention: Draft 1 References Akshoomoff, N.A. (2002). Selective attention and active engagement in young children. 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