Inclusion Criteria:  Healthy adults ages 18-60 years of age living within 20 miles of the Emory Sleep Center in Atlanta, Georgia. Normal body mass index (BMI) (>= 18.5 and <= 28.0 kg/m^2) at screening visit. Has regular sleep-wake habits (e.g., 7-8.5 hours nightly sleep, consistent bed/wake times within 1-2 hours, regular bedtime between 9:30pm-11:30pm, does not oversleep by > 2 hours on weekends). Does not require regular sleep aids or wake promoting medications (including some over the counter cold/allergy medications).  Exclusion Criteria:  Has a history of diagnosed or suspected sleep disorder (e.g., sleep-related breathing disorders, circadian rhythm sleep-wake disorders, central disorders of hypersomnolence, parasomnias, sleep-related movement disorders, disorders of sleep maintenance or initiation) or other medical condition associated with excessive daytime sleepiness. Regular caffeine consumption > 200 mg per day (1 cup of coffee = 80-120 mg). Has a history of major psychiatric disorder (e.g., major depression, bipolar disorder, schizophrenia) or suicidal ideation. Current or recent (within the past 6 months) substance dependence (including nicotine, marijuana, alcohol, or any other substance that is likely to affect sleep). Has a history of diagnosed or suspected attention deficit/hyperactivity disorder. Has performed as a nighttime shift-worker within the past 6 months. Inability to safely tolerate wearing earbuds due to recent injury, skin breakdown, or infection.