It's hard to tell what babies are thinking and how good their memories are, since they can't yet communicate verbally. However, research into memory development in babies has given some clues as to when short-term and long-term memories form and how memory development can be promoted and encouraged by parents.
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Researchers investigating memory development in babies have gotten around the communication problem by studying habituation. These types of studies look at how a baby responds to new stimuli and seeing if they respond in the same ways when they hear or see the same stimuli later. If babies act as though it is an entirely new experience, that indicates that they have no memory of it. Babies who respond as though they have seen or heard that thing before are presumed to be remembering it from the first time. Infants exhibit their level of habituation by staring longer at objects they have never encountered before and ignoring objects that are familiar. In the womb, habituation is exhibited when a fetus responds with movement to unfamiliar stimuli and does not move when exposed to familiar stimuli. This movement is observed via ultrasound while researchers expose the pregnant woman's abdomen to sound or vibration.
Another form of baby memory is deferred imitation, which is when a baby is shown how to do something, such as play with a particular toy in a specific way, and is given the opportunity to do the same thing later. If the baby does the action in the same way, he is presumed to remember the original lesson. Twelve-month-olds exhibit deferred imitation, with babies remembering 70 percent of new activities shown after a three-minute delay and 50 percent after one and four weeks, according to a 1999 study in the journal Developmental Science.
A July 2009 study in the journal Child Development found that even in the womb, babies have started to develop short-term memory. Babies at 30 weeks' gestation became habituated to a combination of noise and vibration in the study, with this habituation lasting until after birth. The particular neurons involved in memory form at the start of the third trimester, leading researchers to believe that this period is the start of actual memory formation in a baby.
Newborns can recognize some things that they have heard first in the womb, indicating at least some level of short-term memory. A typical newborn baby will recognize his mother's voice and other sounds that he has heard frequently from the womb.
At 6 to 12 months, a baby's memory skills are developing even further, leading to the recognition of familiar places and people and the resulting emotional reactions to those things. For example, although he may not remember specifics, a baby between 6 and 12 months may start to exhibit fussiness when brought to the doctor's office where he receives vaccinations or start smiling when he sees Grandma, who he is beginning to associate with cuddles and praise. By a year in age, a baby starts to put together language and memory and may mention a word associated with a place, such as saying "cookie" when arriving at a grandparent's home if he has received cookies there on previous occasions.
Because most memories in babies are only stored as short-term memories, the development of a child's "first memory" doesn't generally occur until about age 3. The memories of a baby are left inaccessible, since the brain structures that hold them permanently in the mind are not formed until later.
Parents interested in developing their baby's memory and trying to unlock communication with a child who may be remembering things but unable to let anyone know yet can try some memory-boosting exercises and games. These can include things like playing peek-a-boo or hiding objects while the baby is watching, such as under a blanket, for the baby to remember and find. Baby sign language is another way for parents to help older babies develop their working memory, since the ability to communicate is tied to how well babies remember things.