Description

Investigators will conduct a 4-group randomized, controlled trial including 200 children (8 to 11 years; Tanner stage 1 or 2) assigned to an unfiltered bright light screen (BL; 109 lux) or a dim light screen (DL; <5 lux) condition in room lighting (40-50 lux) matched with either calming (CC) or exciting content (EC). Children will participate in two weekend protocols, an experimental and a control weekend. During the experimental weekend, children will be exposed to 1 hour of tablet use in the hour before bed under the following conditions: 1) unfiltered bright screen light and exciting content (BL/EC), 2) unfiltered bright screen light and calming content (BL/CC) 3) filtered dim screen light and exciting content (DL/EC) and 4) filtered dim screen light and calming content (DL/CC). To control for the effect of screen media which is common to all 4 conditions irrespective of screen brightness and the nature of the content, each child will undergo a "control condition weekend" in which the child will participate in the same weekend study protocol, but instead of using screen media in the hour before bed, children will participate in non-screen based quiet activities in room lighting (40-50 lux). The control condition will serve as a negative internal control. The order in which children are exposed to the experimental or control weekends will be randomized (i.e., counterbalanced) to control for possible order effects.

Following a week of typical sleep and media use, a 3-day weekend protocol will be implemented in the home facilitated by research staff on two occasions (one week apart, counterbalanced). To assess a potential shift in circadian phase, dim light melatonin onset (DLMO; time at which melatonin level rise above 4pg/mL) will be assessed by research staff on Nights 1 and 3 of the weekend protocol via saliva samples collected under tightly-controlled dim light conditions (i.e., DLMO-Night 3 to DLMO-Night 1). To facilitate the assessment of circadian phases under dim light conditions (<5 lux), research staff will place temporary covers over windows and adjust the lighting in the child's bedroom. A light meter will be used to ensure appropriate lighting conditions.

On Night 2, children will be exposed to either the experimental condition to which they were assigned or the control condition. A background of room lighting (40-50 lux) will be common to both the experimental and control condition.

During the experimental condition, children will exposed to screen media according to the experimental condition they were assigned (BL/EC, BL/CC, DL/EC, DL/CC) via a handheld tablet (at eye level, 45 cm in front of the child). To standardize the distance of the iPad from the eye across participants, the tablet (or non-screen-based activity) will be placed on an adjustable bed desk at a distance of 45cm from the eye. Children will sit upright in bed with a pillow behind them. A similar posture will be used in the control condition. Assessments on Night 2, will be as follows: 1) children's sleep will be assessed via actigraphy, 2) children's arousal will be assessed via heart rate (HR), and heart rate variability (HRV) 3)subjective sleepiness ratings will be collected before the start of the experimental condition, after 30 minutes, and again at bedtime. 4) ambient light will be assessed via a light sensor clipped onto the shirt collar. The next afternoon, emotion regulation (subjective reports and respiratory sinus arrhythmia; RSA) and executive functioning (neurocognitive testing) will be measured to assess these secondary outcomes. Research staff (in teams of 2) will be present in the home to conduct the circadian phase assessments, administer the experimental conditions on the Night 2, and to conduct the executive functioning and emotion regulation assessments in the afternoon of Night 3.

During the weekend protocols, children will be able to participate in daytime activities as usual with the exception that on days when melatonin is assessed, children will be asked to refrain from strenuous physical activity as this is known to affect melatonin.

During the week prior to each weekend assessment, the procedures will be the same for all participants. Parents will select a bedtime and wake time for their child based on their habitual sleep times (+/- 30 mins). Families will be asked to maintain this sleep schedule for the duration of the 2-week protocol, except on nights when DLMO is assessed. Adherence to sleep/wake patterns will be assessed via actigraphy. Because previous exposure to light and screen media can impact future responsiveness to light and screen media, the research team will assess children's ambient light exposure using a reliable sensor clipped near the shirt collar. Mobile device screen use will be assessed using an app downloaded onto the tablet. Other types of screen media use will be assessed by parent report. Variables assessed during the weeks preceding the experimental weekend will be used as covariates in the analysis.

While 200 children are needed to be powered to examine the interaction effect of light and content on children's total sleep time, an additional 20 children will be recruited to account for attrition. The total sample size will be up 220 children.