"Parentese"—that high-pitched, exaggerated language that moms and dads innately use around their newborns—may do more than just annoy nonparents. A study from Virginia Tech University in Blacksburg found that babies may learn from this happy talk more readily. When new words are spoken in a chipper, singsong tone, babies as young as 11 months are better able to recognize those words later, the study showed. When you exclaim cheerfully, "Steamed broccoli! Yum!" for example, your child is encouraged to eat and you may be helping him learn the word "broccoli" in the process.
By contrast, sad-sounding, low-pitched language spoken in a monotone voice doesn't seem to register, says study author and psychologist Naureen Bhullar, Ph.D. So if you say "I guess I'll do the laundry" in the dull voice of Eeyore in Winnie the Pooh, your baby likely won't pick up much.
"Sad speech may not be as conducive to learning at this age," Bhullar says.
Something else to keep in mind: Kids can detect fear and anger in your voice. When you shout "That driver wasn't looking! He could've hit us!" your baby may not understand what happened, but he's likely absorbing the intensity of the emotion and may even get upset.
How it works
If you loudly yell when your baby crawls too close to the steps, causing him to cry, don't feel bad. The fear he heard in your voice is likely what stopped him from going any farther.