Based on earlier observations regarding sex differences in sustained attention across various age groups, we investigated performance differences among children. Furthermore, given that sustained attention is sensitive to sleep loss, we objectively evaluated sleep quality and time in bed using actigraphic objective measurements. The time in bed of weekdays and weekend reflected the recommended time in bed (more than 9.5 h) [35].
Our findings supported the first hypothesis by showing no sex differences in sleep patterns. These findings are in line with previous reports suggesting no sex differences before puberty. For example, Jenni and LeBourgeois [36] reported no sex differences in sleep EEG power bands in prepubescent boys and girls, and Feinberg et al. [37] reported no sex differences in NREM delta power between ages 9 and 11. The authors suggested that the emergence of sex differences at puberty are due to sexual maturation. Furthermore, the authors also suggested that sex hormone regulatory mechanisms may play a role in the decline of NREM delta power density.
Next, we examined the association between sleep duration and PVT performance. In accordance with previous meta-analyses [19, 20], we did not find any correlation. While among adults and adolescents sleep loss results in inattention, among children domains typically sensitive to sleep loss, such as sustained attention, show no significant relationship with sleep duration. Astill et al. [19] suggested that sustained attention requires activation of the frontoparietal networks that are compromised following sleep loss among adolescents and adults, whereas in children this network is still quite immature.
Our second hypothesis regarding sex differences in PVT performance was also confirmed. Under sleep satiation, boys presented shorter PVT RT and fewer lapses than girls, while girls showed fewer false starts than boys. This is in accordance with previous studies which demonstrated that boys are faster and have fewer lapses on sustained attention tasks. For example, Lin et al. [18] examined performance on the continuous performance test (CPT) of children aged 6–15, while Venker et al. [7] examined performance on the PVT of children aged 6–11. Both studies documented sex differences in sustained attention in favor of boys. However, not all studies yielded this pattern of differences between boys and girls (e.g. [14, 15]). These two studies, for example, used different versions of the CPT. Their inconsistency may be due to differences in the measures of each stimulus used; for example, the nature of commission errors and time length of administration for the PVT are different from the CPT [38]. Recently, Rouse et al. [39] used both PVT and CPT to evaluate the effects of medication on attention and other aspects of cognitive functioning among children diagnosed with excessive daytime sleepiness. They found that specific measures of each test indicated other aspects of improved attention in the medicated group. Specifically, the PVT false starts indicated an increase in attention, vigilance, and alertness, and CPT omissions indicated a decrease in the failure to respond to stimuli while children were medicated. These findings call for further research directly comparing PVT and CPT among children to deepen our understanding of the multiple aspects of sustained attention.
We further found that sex difference in PVT RT was moderated by the time of day. Sex differences favoring boys were apparent at morning, while no sex difference was found in the evening. We turned to literature on individual differences in chronotype to shed light on these results. A meta-analysis suggested a significant effect of sex on morningness, with men tending to score significantly more toward eveningness than women [40]. Other studies focused on the role of chronotype on cognitive abilities. For example, Preckel et al. [41] reported a positive association between eveningness and cognitive ability, while Roberts and Kyllonen [42] found that higher scores on eveningness were associated with higher scores on a working memory task, even though the task was performed in the morning. These results suggest that there may be an interaction between sex and chronotype on cognitive performance. To address this Escribano and Díaz-Morales [43] examined the role of sex and chronotype on sustained attention among adolescents. They found that boys presented higher attention levels than girls and that evening type boys tended to perform better than morning type boys and evening type girls even though they were tested in the morning. While the present study did not include chronotype, it should, in our opinion, be considered in future studies. The current preliminary results among children call for replication in future studies including variables such as chronotype, sex, age, and time of day and their interaction exploring their role in attention performance.
We also detected sex differences in the number of PVT false starts, with girls having less false starts than boys. This finding is consistent with previous studies among adults, showing that women commit fewer false starts in vigilance performance than men (e.g., [44]). Blatter et al. [5] explored sex and age differences in the PVT and showed that women tended to inhibit their PVT response to maintain accuracy while men demonstrated faster RT than women. The authors suggested that women and men may use different strategies to achieve optimal results. This is in line with sex differences found in other cognitive domains. For example, Adam et al. [45] demonstrated sex differences in choice RT. Participants performed RT tasks that required a verbal response to a spatial location target stimulus. Men and women showed different RT patterns as a function of stimulus location, and the authors suggested that this may reflect differences in processing strategy. Support for this assertion comes from neuroimaging studies that showed increased activation in temporo-occipital, posterior cingulate, and cerebellar cortices in females in comparison to males during cognitive control and sustained attention contrast tasks [46].
As expected, our results showed sex differences in PVT measures for weekend and weekend nights. While previous meta-analyses [19, 20] did not find an association between sleep duration and sustained attention among children, they did document an association with other cognitive domains (e.g., executive function). We therefore hypothesized that a sex difference effect would be found for both weekend and weekday nights regardless of sleep duration. Investigating differences in sleep patterns in the present sample revealed no significant effect; in other words, our participants had sufficient sleep duration [35] on both weekend and weekday nights. As a result, we had no further opportunity to explore the role of sleep loss in the association between sex differences and sustained attention. Future studies should pursue this objective by including various populations with a range of sleep duration.
Despite its important findings, certain limitations of this study should be noted. First, despite the fact that studies investigating characteristics that may vary significantly within populations often require larger sample sizes, the current study has a small sample size. Interpretations should thus be made with caution. Second, regarding sample characteristics, the children participating in the present study were healthy and were good sleepers. The extent to which our findings can be generalized to other populations is therefore unknown. Third, the children were recruited from middle-class communities with sleep regimes that supported sufficient time in bed on both weekend and weekday nights. Parental supervision has been found essential for the maintenance of healthy sleep habits over time [47]. Future studies should examine other populations to assess the role of sleep deprivation on sex differences in sustained attention. Lastly, the present study did not include an examination of personality traits. A few studies have found a correlation between sustained attention and personality traits, such as the Big Five conscientiousness [48]. Furthermore, previous studies exploring sex differences in cognitive performance and controlling for personality variables have documented the mediating role of personality traits in the relationship between sex differences and cognitive performance (e.g., [49]). However, there is, to the best of our knowledge, no previous report on the role of personality traits in the association between sex differences and sustained attention. We recommend future studies to explore the mechanisms underlying sex differences in sustained attention.