Baby's Brain in Week 4
Even before your baby was born, her senses were working. As early as week 25 of gestation, fetuses can hear their mothers' voices resonate from within the womb, and they hear voices on the outside: could be Daddy, Grandma, siblings, even Mom's coworkers. By now, your baby's sense of taste is well-developed, too; he's able to differentiate among what limited tastes he's been offered up to this point.
And amazingly, Baby's nose develops right around the beginning of the second trimester. (Can you imagine how teeny it was then?) But at birth, it's not just that Baby can hear and smell that's impressive, but that he knows one person's voice and scent from another's—namely, yours. Here's how we know so much about infants' senses.
What the Research Shows
Sound: In evaluating a baby's ability to decipher one voice from another, researchers hooked up an audio device up to a pacifier, as they did with video in the familiar face study. When the babies sucked on the pacifier, they heard the voices of either their moms (or familiar caregivers) or a stranger. The results showed that babies were interested in all voices, but if the voice belonged to someone they knew, they sucked harder and longer.
Smell: To determine babies' abilities to discern among scents, researchers placed a pad on each side of the babies in the study. One held the scent of the mother and the other the scent of an unfamiliar person. They found that baby after baby turned her head toward the pad holding the mother's scent.
We now know that Baby can literally sniff you out, and that he is comforted by familiar voices and smells. He knows, instinctively, "The person behind this voice and scent will do whatever it takes to meet my needs. Phew!"
Taste: Researchers presented newborn babies safe solutions that respectively tasted (even to adults) sweet, sour, and bitter. They did so in the first hours after the babies were born, before they had ever tasted milk from a bottle or from their mother's breasts. The newborns exhibited the same reactive facial expressions as a grown-up would:
- When a tiny amount of the sweet solution was put on each baby's tongue, their facial expression looked like a smile. Plus, the newborns would lick their upper lip, making loud, happy, sucking sounds.
- When tasting the sour solution, the babies pursed their lips, scrunched their noses, and blinked their eyes.
- The response to the bitter taste was quick and dramatic: Upon it touching their tongues, the infants would retch or spit, clearly rejecting it. (Interestingly, it appears that nature equipped babies with this dramatic response to bitter tastes as a survival technique. By welcoming the sweet taste of their mother's milk (or formula), a baby grows and thrives. Conversely, by naturally rejecting anything that tastes bitter, they're more apt to survive—as nothing bitter will benefit their heath and development at this young age and actually could be poisonous. Sour tastes don't evoke quite the same rejection as bitter ones, but those pursed lips indicate that Baby wants to keep that taste away from her tongue.)
Week 4 Brain Booster
With respect to your baby's smelling and hearing skills, there's no need to go bottle your scent or podcast your own lullabies: Just realize the importance of your presence. Talk to your baby as you carry, change, and feed her; hearing you is calming and reassuring. And know that in your everyday routines, the items Baby wears and touches most likely hold your scent already. (It's no wonder she's so cuddly with you!)
Taste can be a little trickier: For example, if your doctor determines your infant needs to switch to soy formula for any reason, Baby will likely reject its bitter taste at first. In time, however, he'll drink it down. And once it becomes his familiar source of nutrition, he'll actually prefer it to sweeter milk. You'll experience a similar pattern of initial reluctance when it's time to introduce (comparatively) bitter vegetables to your baby around six months—you'll likely appreciate this practice then!
Week 4 Tool Kit
Related skills and topics this week include …
Curious about how else Baby might be developing right now? Learn more about her brilliant brain and her growing body here: