Overview
The purpose of this study is to investigate whether the experience of a daily time delay can affect our internal circadian rhythm.
Eligibility
Inclusion Criteria
- Healthy adults aged 23-45 years
- Part of a heterosexual, cohabiting couple willing to participate together in a five-day in-laboratory study
- Both partners meet all inclusion criteria
- Completion of at least upper-secondary education
- Maintain a regular sleep-wake schedule
- Habitual sleep timing within a normative range (non-extreme chronotype), assessed using the Morningness-Eveningness Questionnaire (MEQ) or the Munich Chronotype Questionnaire (MCTQ)
- Both partners fall within the acceptable chronotype range to ensure aligned sleep-wake patterns
- Low seasonality scores on the Seasonal Pattern Assessment Questionnaire (SPAQ)
- Free from underlying sleep or mood disorders
Exclusion Criteria
- Engages in night-shift work or maintains an irregular work or sleep schedule
- International travel involving a time-zone change of more than two hours within the past two months, or anticipated travel before study completion
- Diagnosed neurological, psychiatric, or sleep disorder (e.g., insomnia, sleep apnea, bipolar disorder)
- High risk of sleep apnea, defined as a Berlin Questionnaire score \>2 (Lauritzen et al., 2018)
- Use of medications known to affect sleep, alertness, melatonin secretion, or circadian timing
- Unable or unwilling to comply with behavioral restrictions, including refraining from electronic devices displaying time cues unless clocks are removed and devices are disconnected from Wi-Fi
- Unable or unwilling to comply with consumption restrictions, including abstaining from caffeine, alcohol, and melatonin-rich foods during the study
- Extreme chronotype, defined as a habitual midsleep time outside 03:00-05:00 on the MCTQ or classification as an extreme morning or extreme evening type on the MEQ
- Daily caffeine consumption exceeding 400 mg (approximately 4-5 cups of coffee)
- Current smoker or smoking within the past six months