Even in the home, ABC News' senior health and medical editor Dr. Richard Besser told "Good Morning America" that parents can play games and make faces with their babies to see that recognition in action.
"Does their face change, do they react? If they don't that's something you need to bring to your doctor," he said. "That can be a clue that something is wrong."
In his office, Besser said he often tries to get his littlest patients to turn their heads and follow his facial cues.
"As a pediatrician, when I'm with a mother and a young baby I'm looking to see if there's a connection," he said.
At Charles Nelson's lab at Children's Hospital Boston, babies help him determine when humans begin to recognize faces not by pushing buttons or pointing but simply by looking at pictures on a screen.
Cameras embedded in the screen track the baby's eye movements within a millimeter of accuracy as they examine the faces as a computer logs the child's brain activity.
By comparing changes in eye movement and brain activity for each picture, Nelson can determine when and for how long a child recognizes a difference in a face -- such as in a happy face or a frightened face -- and when a child misses those subtleties.
"There are individual differences to sensitivity to faces, and our hypothesis is they have the origins early at life," said Nelson, a professor of pediatrics and neuroscience at Harvard Medical School.
Nelson said children may start distinguishing faces by species, gender, race and age by their first birthday. However, there's a tradeoff: The more specialized humans become in recognizing some faces, the more they sacrifice their ability to recognize other faces.
"If I showed you [an adult] two different monkeys, you would have a difficult time distinguishing the two faces. You could do it, but it would take time," said Nelson, who has a doctorate in developmental and child psychology.
However, "at 6 months of age, a baby can easily discriminate two monkey faces, but at 9 months, it's difficult for them," he said.
Nelson's work has shown that infants are capable of distinguishing happiness, fear, anger, sadness and disgust even before they can speak. Humans are especially good at recognizing fear.
Babies are More Fixated on Fear
One baby in the study, 8-month-old Emmett, was shown images depicting three different facial emotions.
He seemed more interested on the one showing fear.
"Babies like to look more at fear, and they show more brain activity to fear," Nelson said. "And we've been puzzled by this. They don't seem ... at all upset or alarmed looking at it, they just look at it more."
He isn't sure why babies pay more attention to fearful faces, but Nelson hypothesizes it is hardwired into children's brains to protect them. The faster a child picks up on mom and dad's fear, the faster the child realizes there's danger.
"It's critically important, long before you can fend for yourself, to say, 'That's a face that I need to be concerned about. I don't know why, but, at some point, I'm going to know that I should run away from a face like that,'" Nelson said.
The amygdala, an almond-shaped structure deep in the brain, provides the ability to read emotions, and it gets better at it with experience. A baby's brain is wide open to learning -- unlike an adult's brain -- so if a baby doesn't get the kind of exposure to the various expressions, the child's ability to differentiate between facial expressions may not develop as strongly.
Skill is Important for Survival
"There's actually some evidence to suggest that you can't make up for it," Nelson said.
The skill for reading expressions is valuable. A skilled face-reader will have a better chance at relationships, getting a job and interacting with others, he said.
"Even as adults, we depend heavily on reading faces, and it's because the verbal channel can't always be depended on, because people can disguise that," he added. "They have a harder time disguising their face."
Nelson hopes the research will lead to early diagnoses for autism.
"We hope to see a signature in their brain, or in their eye movements, that will say, 'This is the baby that we're most concerned about,'" he said. "And we can then actually predict who will develop the disorder a year later."
Environment Influences Child's Ability
Results from Nelson's experiments also have shown that a child's environment can influence their ability to read faces.
Children who were physically abused at a young age have proven to be much faster at detecting an angry face than a child who was not abused.
Nelson said researchers in Kentucky found that while most infants prefer female faces, babies raised by stay-at-home dads preferred male faces.
But nurture isn't everything. Scientists also have found that genetics may play a role.
For example, scientists recently have discovered that the 5-HTT gene, which codes for the powerful brain chemical serotonin, can determine the risk of depression. Each person has two copies of the gene, called alleles, and each copy can vary in length. Get a short-short combination of 5-HTT and you're at higher risk for depression than if your get a long-long combination.
Nelson thinks 5-HTT also may influence a child's ability to decipher emotions on faces.
"If you have short-short, you show more brain activity for fearful faces than if you had long-long," said Nelson.
Despite all of Nelson's discoveries, he said his lab and others have yet to try testing a child's ability to recognize deceit. According to other scientists, it may be difficult to study lying through facial recognition alone.
"There is no facial indicator of deception. There's nothing that you do with your face when you're lying that you don't do at other times," said Jeff Cohn, a professor of psychology at the University of Pittsburgh.
Deception Is Difficult to Read in a Face
Cohn works with computer scientists to classify, analyze and detect emotions on people's faces, including pain and clinical depression. Rather than look at still photographs, Cohn said it's easier to detect deceit through the order and intensity of facial movements.
For example, take a person's smile when they receive a gift.
"If they tell you how much they loved your gift and if the smile is missing the contraction of the sphincter muscle around the eye -- the crow's-feet wrinkles -- the person probably wasn't so keen on your gift," said Cohn.
Cohn uses a method called Facial Action Coding System [FACS] developed by famous researcher Paul Ekman to train students to detect such signals. But Cohn warned it isn't something that can be picked up in a day.
"It is something that can be learned," said Cohn. "When we train people in the lab, typically it would take a semester."