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Keywords:

  • children;
  • psychomotor vigilance task;
  • response time;
  • sleep restriction

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Methodology
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The impact of sleep restriction on sustained attention in children has not been well quantified. To address this shortcoming, this study tested the sensitivity of a 5-min personal digital assistant-psychomotor vigilance task (PDA-PVT) to sleep restriction in 14 female children [mean (SD) age = 10.6 ± 0.3 years]. The children underwent PDA-PVT trials at regular intervals both before and after a sleep restriction (5 h time-in-bed) and a control (10 h time-in-bed) condition. Sleep restriction was associated with longer mean response times and increased number of lapses. These results are consistent with findings in the adult literature suggesting an association between inadequate sleep and impaired functioning. In conclusion, the 5-min PDA-PVT is sensitive to sleep restriction in pre-adolescent female children supporting the utility of the PDA-PVT for examining the impact of sleep deprivation on daytime functioning in children.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Methodology
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

There is emerging evidence that children are sleeping less with data from one recent Australian study indicating a 30-min decrease in sleep length over the period 1984–2004 (Dollman et al., 2007). Given the importance of sleep in child development, the long-term consequences of this marked change are unclear. A review of the paediatric literature suggests that sleep restriction is associated with impaired attention, alertness and behaviour, and reduced academic performance (Meijer et al., 2000; Sadeh et al., 2000, 2002; Wolfson and Carskadon, 1998). However, this literature remains to be expanded, and, in particular there is a need to include more objective measures of attention and alertness. A potential candidate that has been widely trialed in adults is the psychomotor vigilance task (PVT) (Dinges and Powell, 1985; reviewed in Dorrian et al., 2004). In adults, the PVT is reportedly sensitive to sleep pressure and circadian timing (Caldwell et al., 2003; Graw et al., 2004; Lamond et al., 2004, 2005). The PVT can be easily administered using a small portable hand-held device [e.g. personal digital assistant-psychomotor vigilance task (PDA-PVT)]. Taken together, these features make the PVT attractive for studying the impact of sleep restriction in children.

Despite its potential utility, the literature examining PVT in children is limited. In a single study of its kind, Venker et al. (2007) report that a 10-min PVT (PVT-192) trial was well accepted in a normative sample of 162 children aged 6–11 years. Despite this promising start, the utility of the PVT in children requires further validation. Importantly, it is yet to be established whether the PVT is sensitive to sleep loss in children. Therefore the aim of this study is to investigate the impact of acute sleep restriction on PVT estimates of sustained attention in a cohort of healthy children.

Methodology

  1. Top of page
  2. Summary
  3. Introduction
  4. Methodology
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Subjects

To control the possible influences of gender the sample was restricted to girls (Venker et al., 2007). Seventeen potential participants were recruited from a South Australian Junior School and were screened using a child sleep behaviour and disturbance questionnaire developed by our group and the Sleep Disorders Scale for children (SDSC) (Bruni et al., 1996). The SDSC assesses sleep behaviour over the preceding 6 months and has six subscales: (i) disorders of initiating and maintaining sleep; (ii) disorders of sleep breathing; (iii) disorders of arousal/nightmares; (iv) disorders of sleep-wake transition; (v) disorders of excessive somnolence; (vi) sleep hyperhydrosis and a composite global sleep disorder score (Bruni et al., 1996). All children recorded subscale and total t-scores below the clinical cut-off (i.e. <70th percentile; Bruni et al., 1996). From this initial sample two children withdrew because of vacation commitments and one because of illness leaving a final sample of 14 children [mean (SD) age = 10.6 ± 0.3 years]. The study was given approval by the Human Research Ethics Committees of the University of South Australia and the Adelaide Womens’ and Childrens’ Hospital.

Design

A repeated measures counterbalanced cross-over design was used to assess the effect of sleep restriction on sustained attention [as indicated by PDA-PVT response time (RT) and lapses >500 ms]. Subjects participated in two conditions separated by at least a week: sleep restriction (5 h time-in-bed) and control (10 h time-in-bed).

Materials

Sleep

Sleep was assessed prior to each condition using 6-day sleep logs completed by parent and child and on the treatment nights using activity monitors (Actigraphs) (Actiware®-Sleep 2000; Mini Mitter Co., Inc., Sunriver, OR, USA). Actigraphy has been established as a reliable and objective method for the naturalistic study of sleep and wakefulness in studies involving infants and children (Acebo et al., 2005; Hyde et al., 2007; Sadeh et al., 1995). The Actigraph is a watch-like device worn on the non-dominant wrist that uses a piezo-electric beam to detect physical movement every 125 ms; movements are represented numerically and summed over predetermined intervals (epochs) to produce estimates of sleep/wake activity. In this study, activity data were binned in 1-min epochs and the Actiware®-Sleep software provided with the Actigraph device was used to obtain sleep/wake parameters, including sleep onset (defined as the absence of movement for three consecutive minutes after lights out), sleep offset (or final wake-up time), sleep onset latency (time taken to fall asleep), sleep period (difference between sleep onset and sleep offset), total sleep time (sleep period less all period of wakefulness during the night) and sleep efficiency (percentage of total sleep time divided by sleep period). Hyde et al. (2007) have validated the Actigraph device and software against polysomnograph in children aged 1–12 years and report that it is a reliable method for determining sleep in children.

Sustained attention

Sustained attention was measured using PVT software (Thorne et al., 2005) on a PalmTM TungstenTM E Handheld (Palm Inc., Mississauga, ON, USA and Sunnyvale, Canada) device. This device has a small LCD screen and is easily portable. The PVT task requires the user to immediately push a prenominated button in response to a visual stimulus (bullseye), programmed to appear at random interstimulus intervals between 2 and 10 s (Lamond et al., 2005, 2007; Thorne et al., 2005). Consistent with standard methodology in adults, a 5-min PDA-PVT was used to measure two parameters of sustained attention: RT (stimulus to button press latency) and number of lapses (RT > 500 ms) (Lamond et al., 2005, 2007). Either premature responses or responses occurring within 100 ms were recorded as ‘false starts’ and not included in the data analysis.

Procedure

The study was completed at the Sleep Disorders Unit at the Womens’ and Childrens’ Hospital of South Australia. Children attended the unit for three nights (17:00–10:00 hours): two consecutive adaptation and treatment (control or sleep restriction) nights followed 1 week later by a further treatment (sleep restriction or control) night. Bed time was delayed in the sleep-restricted group, i.e. 02:00–07:00 hours (5 h time-in-bed), compared with the control, i.e. 21:00–07:00 hours (10 h time-in-bed), condition. The duration of wake time before the first test trial in both treatment conditions was 35 min.

The PDA-PVT was preprogrammed with dominant hand preference, and trials were performed at 18:30, 20:30, 07:30 and 09:30 hours on both the control and sleep restriction night. Although not reported, additional trials were also preformed on the sleep restriction night at 22:30 and 00:30 hours. The participants were instructed to concentrate on the screen for the duration of the test and upon the presence of the visual stimulus (target bullseye), press the button as quickly as possible without attempting to preempt the task. The participants were seated in a room alone, facing a blank wall. Children’s responses were recorded and stored in the PDA device and were downloaded onto a computer after each testing condition by the administrator of the research. The children underwent three learning trials on the evening of the adaptation night and one trial on the following morning. Previous research in adults has indicated that three trials are sufficient training to account for learning effects (Dinges et al., 1997; Kribbs and Dinges, 1994).

Children were provided with dinner at 18:00 hours and breakfast at 07:00 hours and an additional snack on the restriction sleep night at 23:00 hours. Children were not permitted to consume caffeinated and high-energy products while in the unit and were instructed to refrain from caffeine and high-energy products prior to the study night. Children were instructed to maintain a regular sleep schedule for the week preceding the study night and not to nap during the day prior to a study night. Consistent sleep duration (parental report) prior to each condition was confirmed by paired samples t-test (sleep restriction = 9.8 ± 0.7 h and control = 10.1 ± 0.7 h, t = −1.2, > 0.05). Preliminary analyses indicated no significant effect for treatment order (sleep restriction/control versus control/sleep restriction), therefore order was omitted as an independent variable from all future comparisons.

Statistical analysis

Paired sample t-tests were used to test for differences between the sleep diary and actigraphy values observed on the control and sleep restriction nights. PVT data for both RTs and lapses were analysed using repeated measures anova with two within-subject factors (condition and time-of-day). Where a significant effect of time was found, separate repeated measures one-way anova, with planned comparisons to baseline (18:30 hours) were used to test the time points which were significantly different from baseline. Where a significant effect of condition was found, paired sample t-tests were used to determine the time points which were significantly different between conditions.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Methodology
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

In line with the experimental manipulation, treatment night actigraphy data indicated a significantly shorter mean (SD) sleep duration in the sleep restriction (4.8 ± 0.2 h) compared with control (9.2 ± 0.6 h) condition.

To control for intertrial differences, the data were transformed prior to analysis by expressing values relative to baseline. Significant main effects of condition and time-of-day were observed for RTs and a significant main effect of time-of-day on lapses (< 0.05). The anova results are presented in Table 1, the raw RT and lapse values for each condition by time-of-day in Table 2 and the change relative to baseline in Fig. 1.

Table 1.   Results of two within (time-of-day: 20:30, 07:30 and 09:30 hours expressed relative to baseline values at 18:30 hours and condition: control versus sleep restriction) anova with PVT response time (RT) and lapses as dependent variables, together with estimates for effect size and observed power
PVT variableEffectdfFPPartial η2Power
  1. PVT, psychomotor vigilance task; NS, not significant.

RTCondition1, 136.900.020.350.7
Time-of-day3, 393.730.020.220.8
Condition × time-of-day3, 391.71NS0.130.4
LapsesCondition1, 130.00NS0.000.1
Time-of-day3, 394.840.0060.270.9
Condition × time-of-day3, 390.99NS0.070.2
Table 2.   Unadjusted mean (SD) PVT response times [RT (ms)] and number of lapses ≥500 ms for each condition by time-of-day
Time-of-dayCondition
ControlSleep restriction
MeanSDMeanSD
  1. PVT, psychomotor vigilance task.

RT (hours)
 Presleep18:30365.1089.48370.89125.17
20:30404.15103.01417.48178.86
 Postsleep07:30401.11129.67466.79127.02
09:30374.0798.71452.25186.09
Lapses (hours)
 Presleep18:309.578.816.646.99
20:3012.149.5311.3613.38
 Postsleep07:3012.4310.9914.6410.43
09:3012.7910.7614.5012.49
image

Figure 1.  Mean (+SE) response times (RT) in milliseconds (upper panel) and lapses (lower panel) expressed as a change from baseline (18:30 hours) during pre (20:30 hours) and postsleep opportunity (07:30, 09:30 hours) trials. Solid lines represent the control and dotted lines represent the sleep restriction conditions.

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Subsequent analysis revealed that the control condition showed no significant change in RT over time-of-day. By contrast, the sleep restriction condition showed a significant increase [F(3,39) = 2.99, < 0.05] in RT relative to baseline (18:30 hours) at 07:30 and 09:30 hours (planned comparisons, < 0.05). Compared with the control condition, RT were significantly longer in the sleep restriction condition at 07:30 hours [t(13) = −2.90, < 0.05] and 09:30 h [t(13) = −2.36, < 0.05].

Similarly, further analysis revealed that lapses in the control condition did not change significantly over time, whereas the restriction condition showed a significant increase [F(3,39) = 7.73, < 0.05] in lapses relative to baseline (18:30 hours) at 07:30 and 09:30 hours (planned comparisons, < 0.05).

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Methodology
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The main finding of this study is that PVT determined visual motor RT and attention are sensitive to a single night of restricted sleep in young children. Children had slower reaction times and more lapses in the morning following a night of restricted versus control sleep, indicating impaired functioning. This is consistent with expectations based on previous literature (Meijer et al., 2000; Sadeh et al., 2000, 2002; Wolfson and Carskadon, 1998). These findings suggest that the 5-min PDA-PVT is sensitive to sleep restriction in a preadolescent cohort of healthy female children. These findings support the utility of the PDA-PVT as measure of daytime functioning in young children and also offers the possibility that objective measures of performance may be reliably obtained not only in children following environmental manipulation of sleep but also in children with organic sleep problems including periodic limb movement disorders, sleep apnoea syndrome and other occult disorders. In this study we restricted our sample to girls aged 10–11 years. These findings remain to be replicated in younger and older children and males.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Methodology
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We would like to acknowledge the MS McLeod Foundation for supporting Ms Sarah Biggs, use of facilities and support from the staff of the Sleep Laboratory Unit at the Women’s and Children’s Hospital Adelaide and the participating school, teachers and students. In addition we would like to thank Colonel Gregory Belenky and Dr David Thorne for supplying us with The Walter Reed Palm-held Psychomotor Vigilance Task and for all their assistance and support.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Methodology
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • Acebo, C., Sadeh, A., Seifer, R., Tzischinsky, O., Hafer, A. and Carskadon, M. A. Sleep/wake patterns derived from activity monitoring and maternal report for healthy 1- to 5-year-old children. Sleep, 2005, 28: 15681577.
  • Bruni, O., Ottaviano, S., Guidetti, V., Romoli, M., Innocenzi, M., Cortesi, F. and Giannotti, F. The sleep disturbance scale for children (SDSC) construction and validation of an instrument to evaluate sleep disturbances in childhood and adolescence. J. Sleep Res., 1996, 5: 251261.
  • Caldwell, J. A., Prazinko, B. and Caldwell, J. L. Body posture affects electrocenphalographic activity and psychomotor vigilance task performance in sleep-deprived subjects. Clin. Neurophysiol., 2003, 114: 2331.
  • Dinges, D. F. and Powell, J. W. Microcomputer analyses of performance on a portable, simple visual RT task during sustained operations. Behav. Res. Methods Instrum. Comput., 1985, 17: 652655.
  • Dinges, D. F., Pack, F., Williams, K., Gillen, K. A., Powell, J. W., Ott, G. E., Aptowicz, C. and Pack, A. I. Cumulative sleepiness, mood disturbance, and psychomotor vigilance performance decrements during a week of sleep restricted to 4–5 hours per night. Sleep, 1997, 20: 267277.
  • Dollman, J., Ridley, K., Olds, T. and Lowe, E. Trends in the duration of school-day sleep among 10- to 15-year-old South Australians between 1985 and 2004. Acta Paediatr., 2007, 96: 10111014.
  • Dorrian, J., Rogers, N.F. and Dinges, D. F. Psychomotor vigilance performance: neurocognitive assay sensitive to sleep loss. Lung Biology in Health & Disease, 2004, 193: 3970.
  • Graw, P., Krauchi, K., Knoblauch, V., Wirz-Justice, A. and Cajochen, C. Circadian and wake-dependent modulation of fastest and slowest reaction times during the psychomotor vigilance task. Physiol. Behav., 2004, 80: 695701.
  • Hyde, M., O’Driscoll, D. M., Binette, S., Galang, C., Tan, S. K., Verginis, N., Davey, M. J. and Horne, R. S. C. Validation of actigraphy for determining sleep and wake in children with sleep disordered breathing. J. Sleep Res., 2007, 16: 213216.
  • Kribbs, N. B. and Dinges, D. F. Vigilance decrement and sleepiness. In: J. R.Harsh and R. D.Ogilvie (Eds) Sleep Onset Mechanisms. American Psychological Association, Washington, DC, 1994: 113125.
  • Lamond, N., Dorrian, J., Burgess, H., Holmes, A., Roach, G., McCulloch, K., Fletcher, A. and Dawson, D. Assessment of performance during a week of simulated night work. Ergonomics, 2004, 47: 154165.
  • Lamond, N., Dawson, D. and Roach, G. Fatigue assessment in the field: validations of a hand held electronic psychomotor vigilance task. Aviat. Space Environ. Med., 2005, 76: 486489.
  • Lamond, N., Jay, S. M., Dorrian, J., Ferguson, S. A., Roach, G. D. and Dawson, D. The sensitivity of a palm-based psychomotor vigilance task to severe sleep loss. Behav. Res. Methods Instrum. Comput., 2007, 40: 347352.
  • Meijer, A. M., Habekothe, H. T. and Van Den Wittenboer, G. L. Time in bed, quality of sleep and school functioning of children. J. Sleep Res, 2000, 9: 145153.
  • Sadeh, A., Hauri, P. J., Kripke, D. F. and Lavie, P. The role of actigraphy in the evaluation of sleep disorders. Sleep, 1995, 18: 288302.
  • Sadeh, A., Raviv, A. and Gruber, R. Sleep patterns and sleep disruptions in school-age children. Dev. Psychol., 2000, 36: 291301.
  • Sadeh, A., Gruber, R. and Raviv, A. Sleep, neurobehavioral functioning and behaviour problems in school-age children. Child Dev., 2002, 73: 405417.
  • Thorne, D. R., Johnson, D. E., Redmond, D. P., Sing, H. C., Belenky, G. and Shapiro, J. M. The Walter Reed palm-held psychomotor vigilance test. Behav. Res. Methods, 2005, 37: 111118.
  • Venker, C. C., Goodwin, J. L., Roe, D. J., Kaemingk, K. L., Mulvaney, S. and Quan, S. F. Normative psychomotor vigilance task performance in children ages 6 to 11—the Tucson Children’s Assessment of Sleep Apnea (TuCASA). Sleep Breath, 2007, 11: 217224.
  • Wolfson, A. R. and Carskadon, M. A. Sleep schedules and daytime functioning in adolescents. Child Dev., 1998, 69: 875887.