Observational StudyThe Function of Biphasic Sleep in Infants

Inclusion Criteria:

1. 9 months at the time of enrollment
2. normal birthweight (5.5 to 10 lbs) and gestational length (36-41 weeks)
3. must be willing and able to return for testing in 3 and 6 months (e.g., no plans to move out of the area)

Exclusion Criteria:

1. born premature (<36 weeks gestational age)
2. receiving services due to developmental delays
3. visual or motor disability
4. score <85 on cognitive and language composite scales and/or <80 on the average of the two composites of the Bayley Scales of Infant Development Fourth Edition (BSID-IV) administered at the first session.
5. Infants' motor development (gross and fine motor) will also be assessed using the BSID-IV, and an adjusted cutoff of 73 will be used to exclude infants with significant motor delays (given the motoric nature of the task).
6. traveling beyond 1 time zone within 2 weeks prior to testing (phone screening)
7. fever or symptoms of respiratory illness at the time of testing (phone screening)
8. physical handicap that interferes with assessments (vision, hearing impairment; phone screening)
9. history of neurological injury such as history of seizures, brain tumor, or stroke (phone screening) Parents/guardians of potential participants will be contacted via phone and/or email, at which time the details of the study will be specified and inclusion/exclusion criteria will be reviewed.