They found that the majority of words infants heard, directed at them or in the background, came from mothers. Also:

• About one-quarter of vocalizations from infants got an adult response.

• Those responses came from moms alone more than 70% of the time, from both parents 18% to 23% of the time and from dads alone just 6% to 12% of the time.

• Moms responded more often to girls than boys. Dads responded more often to boys, but the difference was so small that the researchers said it was not significant.

The study is small and included only families in which a male and female parent lived together, so it might not represent all families and should be repeated on a larger scale, Vohr says.