"Hello baby, is it dark in there?"
Like reader jackie31337, who asked this question when she was a small child, scientists don't remember what life in the womb was like. If they want to know what a fetus can see—not to mention smell, hear, taste and touch—they have to go right to the source. Unfortunately, the unborn are not the world's greatest communicators.
To find the answers, researchers study animal fetuses, healthy human newborns only hours old and premature infants finishing their pre-natal development in an incubator. What they've learned about the fetal experience and the development of the senses not only expands our understanding of the human body, it's also helping to up the premies' chances for a healthy, normal life.
Across the animal kingdom, senses come online in a very specific order that doesn't vary much from one vertebrate to another. The first sense fetuses experience is touch. Then come the chemical-based senses—taste and smell. The ability to hear develops fourth. And finally, so late that many animals are born lacking it, comes sight.
Humans, with our relatively long gestation periods, are one of the few species that can see before we're born. Not that there's very much to see. The short answer to jackie31337's question is, "Yes. It is, in fact, rather dark in there."
"They can tell the difference between dim and very dim. That's what they'd see if mom removed outer clothing on a sunny day," said William Fifer, Ph.D., head of the fetal/infant development lab at Columbia University's division of developmental psychology.
Scientists have watched fetuses on ultrasound turn their heads away from bright lights held up to their mother's stomach, Fifer said. And they've seen the brain waves of premature infants spike in response to a flash of light, or a change in visual stimulus—switching a card from vertical stripes to horizontal, for instance. Sight isn't much of a sense at this point, but it's enough.
Enough for what? That's where things get interesting. See, senses don't work via some neurological "off/on" switch. It's more like building muscle. You have to exercise to get results. The more you work out the new sense, the more neuron connections are formed and the sense improves. But if you don't use it, you lose it. Literally.
"You need sensory stimulation of some sort, or the nerve connections never form," Fifer said. "Kittens blindfolded after birth never develop sight."
Sensory stimulation is important in other ways as well, helping fetuses learn. For instance, duck embryos peep to themselves while still inside their eggs. As they do that, they begin to recognize what a duck voice sounds like.
"A researcher named Gilbert Gottlieb found that, if he de-vocalized a duck embryo, then after birth it wouldn't be able to tell the difference between the maternal calls of a duck or a chicken," said Jeffery Alberts, Ph.D., professor of psychology at Indiana University. "They have to hear themselves in the egg and stimulate their own auditory systems. That's how they get it to be tuned enough to complete development."
Monkey hear, monkey do
Human fetuses use their senses to learn, too. Christine Moon, Ph.D., professor of psychology at Pacific Lutheran University, studies auditory development in humans. She does her research by staking out the maternity wing at a local hospital, popping in on new families right after babies are born. If the parents are interested, infants as young as eight hours old can be tested to see how they respond to different sounds. The babies wear headphones and are given special pacifiers hooked up to a computer.
Turns out, babies suck harder on the pacifiers when they hear sounds that are familiar to them from before birth. Newborns prefer their mother's voice over anyone else's (even dad's). They prefer hearing phrases from books they were read while in the womb, compared to new stories. They're even already favoring one language over another.
"Babies prefer the sound of their mother's native language to others," Moon said. "Interestingly, they can distinguish between languages in the same rythmic class, like Spanish versus English. But they can't tell the difference between similar sounding languages, like English and Dutch."
Mothers' speech seem to matter in other ways as well. Moms who don't mumble or slur their words together have children that can better recognize consonants at 6-to-8 months, and have bigger vocabularies at 10-to-12 months, compared to their peers. This, and other research, has led Moon to theorize that language acquisition is a process that begins before we're even born.
Seeing a better future
All this has big implications for infant health.
We know now that sensory experiences before birth play a role in making sure senses develop properly and that fetuses learn important post-birth behaviors. That's helped researchers better understand what happens to fetuses exposed to alcohol.
Too much alcohol makes for a fetus that doesn't move around much and interacts less with its environment. That means less sensory experience and, thus, less cognitive development. Like the de-vocalized duck embryo, a fetus exposed to alcohol can't teach itself. That sensory deprivation can even have physical impacts.
"One of the things the fetus experiences from alcohol exposure is reduced swallowing movements. So it doesn't have that stimulation of the gastro-intestinal system to help that system develop normally," Jeffrey Alberts said.
Studying fetal senses has also helped doctors develop better ways of caring for premature infants. These babies end up lacking a lot of the sensory experiences they need for normal development—the movement of being inside their mother, the smells and tastes of the womb, their mother's voice—while simultaneously experiencing bright lights and loud noises that they wouldn't normally. Imagine falling asleep in a hammock on a tropical night, and waking to find yourself being grilled under the light by a noir police detective. That shock makes a difference in babies' development, and helps put them at risk for a variety of cognitive and motor disorders, William Fifer said.
Sensory research has led to darker rooms for pre-term infants, turning down the harsh lights that can harm their not-quite-ready-for-primetime eyesight, Fifer said. It's also prompted hospitals to begin monitoring the babies' brain waves and testing their hearing, looking for early signs that the baby in question might need therapeutic intervention.
"It's only in the last few years that we've been checking that as a matter of course," he said. "Now many nurseries measure brain activity because we know that if you see problems early on you can make a bigger difference."
Photo of 18-hour-old baby participating in a speech/language perception experiment, ,courtesy Christine Moon.