Introduction
The ages of 6 and 7 years old are crucial for fundamental learnings of children. Indeed, the end of kindergarten and the beginning of primary school is marked by the discoveries of reading, writing, and mathematics. Concomitantly, this period corresponds to an important step in cognitive development characterized by quantitative and qualitative changes in several cognitive processes. Indeed, besides an important improvement in processing speed (Kail and Ferrer, 2007), efficient cognitive strategies may emerge in children aged 6 to 7, such as “sorting” or “active refreshing” strategies improving short-term and working memory performance (Schneider et al., 2004; Camos and Barrouillet, 2011). These children start also to use a more proactive cognitive control (Lucenet and Blaye, 2014; Gonthier et al., 2019), by preparing in advance for foreseeable demands of tasks, which is known to require more mental efforts but also to be more efficient for minimizing the effects of interfering information (Chevalier, 2015). These changes are accompanied by an important increase in attention performance (Mezzacappa, 2004). The development literature has consistently shown that executive functions and attention components play an important part in children’s academic achievement (Cartwright, 2012; Franceschini et al., 2012; Kim et al., 2013; Hassinger-Das et al., 2014; Kent et al., 2014; Meixner et al., 2019; Valdois et al., 2019).
Posner and Petersen (1990) identified three functions of attention named alertness, orienting, and executive control, all sustained by distinct neural networks. Thus, alertness refers to the elaboration and maintenance of an optimal level of vigilance to be ready to achieve a task or respond to a stimulus (Raz and Buhle, 2006; Petersen and Posner, 2012; Rueda and Posner, 2013; Barra et al., 2015). It can be divided into tonic alertness [i.e., a general cognitive control of arousal during the task (Raz and Buhle, 2006)] and phasic alertness [i.e., a more transient level of readiness to respond (Petersen and Posner, 2012)]. Alertness is controlled by a norepinephrine pathway from the locus coeruleus to frontal and parietal regions. Orienting is related to the ability to enhance the processing of specific information from sensory input by shifting attention to a particular object, event, or location (Waszak et al., 2010; Barra et al., 2015; Mullane et al., 2016). It is controlled by a ventral network, including the temporo-parietal junction and the ventral frontal cortex, and a dorsal network including the frontal eye field and the intraparietal sulcus (Petersen and Posner, 2012). The third function identified by Posner and Petersen (1990), the executive control, refers to error detection, monitoring, and resolution of conflict in goal setting [e.g., during thoughts, feelings, and responses (Petersen and Posner, 2012; Rueda and Posner, 2013)]. In particular, executive control allows the inhibition of irrelevant response tendencies or distracting stimuli to focus on the task demand (Raz and Buhle, 2006). Two dopaminergic networks, the fronto-parietal and cingulo-opercular networks, are mainly involved in these executive processes. The efficiency of the three functions of attention may be evaluated by a single task with the Attention Network Test (Fan et al., 2002). Notably, Rueda et al. (2004) developed a version of this test for children (ANT-C) to study the development of these functions during childhood.
From a developmental point of view, phasic alertness following a visual warning signal gradually improves until 6years of age, with a second developmental phase during early adolescence (Mezzacappa, 2004; Rueda et al., 2004; Federico et al., 2017; Suades-González et al., 2017; Lewis et al., 2018). When an auditory warning signal was used, an improvement of phasic alertness until 12years of age was evidenced, especially between 7 and 9years (Pozuelos et al., 2014; Mullane et al., 2016). Tonic alertness significantly increases in preschoolers (Rueda and Posner, 2013) but may continue to develop until adolescence for monotonous task, with a significant improvement between 6 and 8–9years old (Lin et al., 1999; Kanaka et al., 2008; Lewis et al., 2017). In contrast, the automatic, exogenous orienting toward targets may be almost mature around the age of 6years (Rueda et al., 2004), even if an improvement between 5 and 7years old was shown (Mezzacappa, 2004). Endogenous orienting guided by internal intentions (e.g., following an arrow pointing toward the target location) and the attentional disengagement and reorienting (following invalid spatial information) continue to develop after 6years old, at least until late childhood (Konrad et al., 2005; Wainwright and Bryson, 2005; Iarocci et al., 2009; Waszak et al., 2010; Pozuelos et al., 2014; Johnson et al., 2020). Finally, it is well recognized that executive functions and abilities of children to resolve conflict strongly improved during early childhood (Carlson, 2005; Diamond, 2006; Garon et al., 2008). Nevertheless, depending on the tasks used, an improvement of executive control during moderate and late childhood was highlighted (Best and Miller, 2010). Notably, studies using ANT-C and Flanker tasks showed a development of executive control between 4 and 9years old (Mezzacappa, 2004; Rueda et al., 2004; Checa et al., 2014; Pozuelos et al., 2014; Mullane et al., 2016; Lewis et al., 2018). Its development may extend throughout adolescence because 15-year-old teenagers are not yet at the adult level (Waszak et al., 2010). Therefore, 6 to 7years of age is a crucial period for attentional development during which alertness is not fully mature, the development of exogenous orienting may be completed, and executive control strongly improves. Many environmental factors may influence attentional development and performance at these ages, such as socioeconomic status (Mezzacappa, 2004) or training intervention (Rueda et al., 2005).
Interactions between postural and cognitive, especially attention, activities were studied in adults (Dault et al., 2001; Mitra and Fraizer, 2004) and in children (Olivier et al., 2010; Fabri et al., 2017). These studies were done with the dual-task paradigm: cognitive and postural respective performances are compared between the separate and the concurrent execution of one postural and one cognitive task. Another method consists in observing how the increase in the difficulty level of one task affects the performance in both tasks (Fraizer and Mitra, 2008). The most common explanation for the results observed is that postural and cognitive activities share a set of limited central processing resources which results in decreased performance of one or both tasks if the amount of available resources is exceeded (Woollacott and Shumway-Cook, 2002). However, this conception is not sufficient for explaining the great variety of results observed (Bonnet and Baudry, 2016). Indeed, some cognitive performances may improve in more demanding postures (Barra et al., 2015) and some cognitive activities cause a decrease in body sway – interpreted as a better postural performance – by diverting attention focus from postural control and increasing automaticity (Richer et al., 2017).
Thus, an alternative and more ecological conception was proposed (Stoffregen et al., 1999, 2000, 2007). Postural activity would be functionally integrated with suprapostural activities defined as the “cognitive activities superordinate to the control of posture” (Stoffregen et al., 1999), that is, cognitive activities other than postural control. For example, postural stabilization may occur during precise perceptive tasks in order to improve visual performance (Stoffregen et al., 2007). Other authors also speculated on a functional role of body sway, interpreted as a self-generated body mobility in order to increase the organism’s arousal (Stins and Beek, 2012; Ceyte et al., 2014). Therefore, postural and suprapostural tasks influence each other and the performance during dual tasks strongly depends on the posture and the cognitive function studied (Stoffregen et al., 2007; Abou Khalil et al., 2020). The differences in body sway between a reading and a counting backward task in children aged 8–10 suggest that postural activity may be modulated to facilitate suprapostural task from childhood (Blanchard et al., 2005).
From the first grade of elementary school, the preferential posture at school (in many cultures) remains sitting still, without moving, because body mobility is supposed to disturb their classwork. However, the use of school desks allowing to freely sit down or stand up did not decrease attention performance (Koepp et al., 2012; Aminian et al., 2015; Wick et al., 2018). On the contrary, teachers and children reported that using these desks improved their attention performance (Blake et al., 2012; Aminian et al., 2015; Verloigne et al., 2018; Wick et al., 2018). Therefore, changing posture during lessons may improve children attention. In adults, an increase in alertness (Caldwell et al., 2003; Barra et al., 2015) and to a lesser extent in executive control performance (Rosenbaum et al., 2017; Smith et al., 2019, but see Caron et al., 2020; Kang et al., 2021) were observed by adopting a standing compared to a sitting posture. These improvements may derive from neurophysiological modulations occurring when standing (Tulen et al., 1999; Hennig et al., 2000; Caldwell et al., 2003; Thibault and Raz, 2016) which may increase the level of general and cortical arousal (Barra et al., 2015; Smith et al., 2019). In addition, the lack of difference between sitting and standing for orienting suggests different effects of body posture depending on the attentional function studied (Barra et al., 2015).
This influence of postural and motor systems on higher-cognitive processes supports that mind is “embodied” in bodily experiences. In the theoretical conception of embodied cognition, actions and sensorimotor experiences determine our major cognitive processes (Brouillet, 2019). The crucial role of bodily experiences is also increasingly highlighted for child development and cognition (Marmeleira and Duarte Santos, 2019). For example, bodily and “embodied” activities may enhance mathematical or scientific learnings (Dackermann et al., 2017; Mavilidi et al., 2017). Interestingly, the improvement of working memory performance when children walk (Schaefer, 2019), especially at an un-imposed speed (Schaefer et al., 2010), and their increased motor activity level during cognitive demanding tasks (Patros et al., 2017) may suggest a functional role of spontaneous body mobility on high-cognitive processes. The improvement of children’s tonic alertness (de Greeff et al., 2018) and executive control (Janssen et al., 2014; de Greeff et al., 2018) after acute physical activities suggests that body mobility may also influence attentional functions.
The aim of this study was to analyze the influence of body posture (standing versus sitting) and the influence of these imposed postures compared to a free body mobility on attentional functions in 6- to 7-year-old children. We hypothesized that alertness and executive control, but not orienting, performance improves with standing compared to sitting. Moreover, with a free to move condition, compared to the instruction to stay still, we expected that children would increase their body mobility, which would improve the efficiency of their attentional functions.
Discussion
The aim of this study was to analyze the influence of body posture (standing versus sitting) and the influence of these imposed postures compared to a free body mobility on alertness, orienting, and executive control in children aged 6 to 7years. Contrary to our hypothesis, children did not significantly improve their alertness, neither when they stood still nor when they moved freely, compared to sitting still. Regarding the function of orienting, as expected, we found no difference between sitting and standing still. A slightly larger orienting score was found when the children were free to move. Nevertheless, in general, children did not respond faster when they were previously informed of where the target would appear. Finally, we expected an improvement in executive control when standing compared to sitting, and without the instruction to stay still. The results showed that children did have improved executive control when standing, but we found no further improvement when they were free to move.
Insufficient Mobility for Improved Alertness?
We found no difference between sitting and standing still for children’s alertness. These results are different from previous reports in adults (Caldwell et al., 2003; Barra et al., 2015). In the one hand, the influence of adopting a standing posture on the level of alertness may differ between children aged 6 to 7years and adults, as their postural control (Assaiante and Amblard, 1995; Olivier et al., 2008; Micarelli et al., 2020) and their function of alertness (Rueda et al., 2004) are yet not fully developed. In the other hand, perhaps the instruction to stay still prevented any improvement in alertness with the standing posture. Indeed, directing the attentional focus toward postural control (termed internal focus) causes a more conscious regulation of posture, which may interfere with the automatic processes of postural control and may disrupt postural and cognitive activities in adults and children (Olivier et al., 2008; Remaud et al., 2013; Wulf, 2013; Burcal et al., 2014; Jehu et al., 2014; Richer and Lajoie, 2020). In addition, the instruction to stay still may require the inhibition of spontaneous or impulse motor responses in children and motor inhibitory control may develop into late childhood and adolescence depending on the inhibition task (Best and Miller, 2010).
It can be noted that the use of sit-to-stand desks at school, which seem to improve children’s alertness, allows them to change posture as often as they want (Aminian et al., 2015). This may allow them to increase their body mobility compared to a standing still posture. In the present study, children did not improve their alertness when they were free to move. Nevertheless, the majority of children moved relatively little, even without the instruction to stay still. Therefore, perhaps that a greater body mobility may be necessary to improve the children’s alertness. The increase in children’s tonic alertness after an acute physical activity may support this assumption (de Greeff et al., 2018). Though the ANT-C allows us to evaluate the functions of attention, this task required also important perceptual (visual) abilities, such as to identify the left or right direction of the target. Therefore, we speculate that, in our study, children limited their body mobility in order to stabilize their head and gaze and facilitate their perceptual activity (Stoffregen et al., 2000, 2007; Bonnet and Baudry, 2016).
Incomplete Maturation of Orienting at 6 to 7Years?
No difference was found between the sitting and standing postures for the orienting performance, consistent with our initial hypothesis. A slightly larger orienting score was found when the children were free to move but this score remains small. Our results suggested that the body mobility condition does not improve the orienting function of children, which revolved around zero. Moreover, contrary to adults (Barra et al., 2015), information on the location of the upcoming target does not help children aged 6 to 7years to orient their attention better. Others studies showed a small orienting score in children at these ages (Mezzacappa, 2004; Ishigami and Klein, 2015), what suggests that the function of orienting may not be fully mature (Ishigami and Klein, 2015). These results are consistent with those of Mezzacappa (2004) which showed a development of the use of spatial information on the upcoming target between 5 to 7years.
Improvement of Executive Control by Standing
Results showed a moderate improvement in executive control when the children stood compared to sitting. These results are consistent with some performance of adults (Rosenbaum et al., 2017; Smith et al., 2019). The executive control level is strongly influenced by arousal (Matchock and Toby Mordkoff, 2009; McConnell and Shore, 2011), which may be increased by a standing posture (Barra et al., 2015). This is consistent with physiological and neural modulations occurring when adopting a standing posture compared to a sitting posture (Tulen et al., 1999; Hennig et al., 2000; Caldwell et al., 2003). Easterbrook (1959) suggested that an optimal level of arousal may allow participants to be receptive of relevant information. This is in agreement with the increase in responsiveness to relevant information for a certain level of locus coeruleus activation (Aston-Jones and Cohen, 2005). Some authors have also suggested that a standing posture may induce a specific mental state in order to facilitate actions afforded by this posture (Thibault and Raz, 2016; Smith et al., 2019). In particular, an increase in information discrimination in the standing posture may support good and fast decision-making (e.g., to engage in fight or flight behavior; Smith et al., 2019). Furthermore, no improvement in executive control was found when children were free to move. In regard to alertness, we can speculate that too much freedom may not be optimal to perform this attention task, with the child requesting spatial reference points. More precisely, in regard to the studied visual cognitive task, 6- to 7-year-old children appear to need an environmental anchor that can hold their spontaneous body mobility.
Limitations and Perspectives
This study has limitations. The relative small sample size and the variability between children, as frequently reported in this age range, may limit the generalization of the results. Further studies with increased number of children will be interesting to validate our results. It can also be noted that IQ of children was not evaluated in this study, especially to limit the experiment duration. Nevertheless, it was confirmed during interview with parents that none child had known cognitive, developmental, or motor disorder and that all children were in their appropriate grade level. Furthermore, the number of ANT-C trials for each body mobility condition was reduced as compared to the trials described by Rueda et al. (2004). We had to adjust the experimental design to maintain a sufficient level of engagement (Ishigami and Klein, 2015) and a reduced level of tiredness because of the young age of the children. Validation of the alerting effect and conflict effect suggests that children correctly performed the task in the three-body mobility conditions. In addition, the intra-individual variability in reaction time (Supplementary Figure S2) remained close enough to the values reported by (Lewis et al., 2018) for children of the same age, despite the smaller number of trials. Also, the free to move condition in this study did not allow us to precisely determine whether the results were related more to the absence of instruction on staying still or an increase in body mobility. Nevertheless, testing the influence of this ecological condition on attention networks is interesting because of its practical implications. We found no decline in alertness or executive control when children were free to move, supporting the idea that increasing the freedom of movement among children at school is not always detrimental. Finally, it could have been interesting to more precisely quantify the children’s movements. Nevertheless, a video analysis by two independent observers is an ecological way of evaluating the gross motor activity of children, easily applicable and reproducible in the practical field, and the inter-examiner agreement was correct in the present study.
As a perspective, it may be interesting to replicate the experiment by studying more than one age range with different schooling experience. This perspective is in accordance with the development of the functions of attention occurring between the ages of 6 to 12years, studies especially suggesting a turning point in middle childhood (Rueda et al., 2004) and in late childhood (Suades-González et al., 2017) for executive control and alertness, respectively. The level of spontaneous motor activity also seemed to undergo changes during childhood, with a gradual decrease of motor activity especially after the middle childhood (around 8years, (Eaton et al., 2001; Brocki et al., 2010). In that way, to compare the influence of body mobility on the functions of attention between the early, middle and late childhood seems interesting.