Furthermore, some researchers question whether exposing infants to constant sound all night could have other long-term effects on development. Animal research has found that prolonged exposure to white noise during infancy can alter the brain's processing of sound and the animal's behavior. Because longer-term consequences are unknown, researchers suggest that before buying a sleep machine parents try to soothe babies to sleep in other ways like warm baths and old-fashioned lullabies. And, if using a sleep machine, Dr. Ronald Hoffman of the New York Eye and Ear Infirmary of Mount Sinai recommends keeping the volume low and placing the machines across the room from baby's crib -- advice which is absent from the products' packaging.
 Pediatrics (online March 3, 2014 and in print April 2014)
 NIH HealthDay, "Baby 'Sleep Machines' Could Damage Hearing, Study Suggests" (March 3, 2014).