From The Parent Review
A baby's first smile is unforgettable. Just a few weeks after birth, that quick, small curve of the lips signals the beginning of a developmental journey that transforms an innate, spontaneous offering into a complex social expression of joy and invitation. A smile is more than charming; it is essential to a child's social and emotional future.
Before 1 month of age, an infant's smiles are predominately an inborn behavior, rather than responses to something he sees, hears or feels. These early smiles, reflexive and unrelated to social interaction, occur most often during deep sleep and the transitions between waking and sleep.
By 2 months of age, however, most babies begin to offer smiles in response to a pleasing or gently surprising external event: the appearance of their mother's face, a favorite toy or a sibling's grin. A combination of visual and auditory stimulation, or sights and sounds, is especially likely to elicit these delighted - and delightful - smiles.
The shift from spontaneous, internally motivated smiles to responsive, externally motivated smiles is due in part to an infant's growing ability to maintain eye contact and visual attention for longer periods of time. As a baby becomes more aware of his world, the frequency of these smiles increases.
Even the responsive smiles of a 2-month-old, however, are still strictly a reflection of the infant's internal response to something engaging. The next phase of smiling, social smiling, launches a baby's ability to share positive emotions with other people. Finally, he is able to communicate his personal feelings to the world at large.
The First Discovery:
When I smile, you smile!
The earliest social smiling occurs between a baby and a parent. Babies love faces; right from birth they will focus intently on their mothers' faces, and even on abstract images arranged like facial features. This kind of brow-knitting concentration is hard work for an infant, so she has two strategies to relax herself: She may look away, giving herself a break from the intense sensory input. Or, she may relax her brow and smile, which also releases tension.
This focus on faces and early ability to self-regulate signal a baby's emotional development and her need to connect to her caretakers. While an infant's smiles during the first two months of life are primarily receptive, reflecting her inner feelings, by the third month of life she begins to use her smiles to elicit an emotional connection. She's learning that smiling and animating her face, hands and voice results in pleasurable attention from her caretakers, and that when she acts in a certain way, she can expect certain responses.
The Second Discovery:
I know when you're going to smile!
Infant smiles become a more complex and useful tool of social communication between 8 and 12 months of age, with "anticipatory" smiles: smiling and then turning toward another person, expecting to receive a smile in return.
Although scientists can't be absolutely certain why anticipatory smiling develops at this age, they have formed a hypothesis. Babies at this stage of development have increasing strength and mobility, and are able to sit and play apart from their mothers. They play, then they look for their mothers, and their mothers look back and smile. They begin to associate the happy arousal they feel during play with looking for their mothers, and with their mothers' smiles. Before long, a baby anticipates the progression and offers a smile before looking in her mother's direction, increasingly certain that mom will be looking and will smile back. This is a simple but powerful lesson for a baby: that her interior feelings can connect her to others, and can shape the behavior of others.
Making these associations - between self and others and between emotion and behavior - fuels the development of an infant's social skills. By 8 months of age, with just a simple glance and expectant smile, a baby declares that she is already a powerful communicator, ready to enter and participate in our highly social world.
Sources: Infant Behavior & Development 28 (2005): 194-205; Developmental Psychology 41 (2005): 265-80.
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