Sleeping babies learn in an eyeblink

Babies snooze through much of the first month after birth, but don’t call them lazy. One-month-olds doze to discover, with an emphasis on social insights, a new study suggests.

Snoozing infants learned to blink in response to three types of sounds, says psychologist Bethany Reeb-Sutherland of the University of Maryland, College Park, and her colleagues. Sleeping babies blinked more readily upon hearing a spoken voice than a tone or a recorded voice played backward, signaling an early aptitude for absorbing social information, the researchers report in a paper published online June 18 in Developmental Science.

“Although young infants spend much of their time sleeping, they continue to learn about the environment around them, particularly the social environment,” Reeb-Sutherland says.

These findings help to explain how infants come to recognize speech sounds within several months of birth, remarks psychologist Carolyn Rovee-Collier of Rutgers University in Piscataway, N.J. “From birth through at least 1 month of age, infants learn while they sleep — an ability that adults lack,” Rovee-Collier says.

Sleep bolsters memories and decision making in adults (SN: 4/28/07, p. 260), but no evidence suggests that slumbering grown-ups can learn new information.

A 2010 investigation led by study coauthor and developmental psychobiologist William Fifer of Columbia University in New York City found that sleeping 1- to 2-day-olds learn to blink in response to a tone played before the delivery of a blink-inducing air puff.

Reeb-Sutherland’s team conditioned blinking in 64 sleeping 1-month-olds exposed either to tones, to a woman’s voice saying “Hi baby,” or to the same salutation played backward. Infants blinked in response to the greeting alone on an average of 12 out of 15 trials. Tones and backward talking elicited blinking on an average of 9 out of 15 trials.

No signs of conditioning appeared in another 13 infants, for whom tones or the greeting were presented randomly before and after air puffs.

Emotional cues in speech may hold special appeal for babies, perhaps explaining superior conditioning to a greeting, Reeb-Sutherland says. It’s also possible that, already having heard a lot of talking adults, dozing 1-month-olds perceive words with particular ease.

Rovee-Collier regards the new findings as consistent with other evidence of “rapid and exuberant learning” up to 10 months of age, with no special advantage for social information. Infants rapidly distinguish native from foreign musical rhythms, a nonsocial feat, she says. Sleeping 1-month-olds probably associate eyeblinks with musical rhythms as well as they do with spoken greetings, Rovee-Collier predicts.

Eyeblink training during sleep shows promise as a way to probe for social and sensory problems in infant siblings of children with autism spectrum disorders, who themselves have a genetic propensity for autism, adds psychologist Wendy Stone of the University of Washington in Seattle.