The Development of Memory in Infants

Memory is not a single entity but a patchwork of several different forms of information storage that emerge progressively with the maturation of different brain circuits. Babies begin life with a primitive yet very useful set of memory skills; lower parts of the brain can store information, but it is at an automatic level, beneath consciousness, and lasts for relatively short periods of time. Then, starting at eight or nine months of age, they show signs of a more flexible, deliberate type of information storage, the first inklings of memory as we more commonly think of it. Memories then grow longer and increasingly conscious throughout the preschool years until finally, during early elementary school years, children become aware of their own memory skills and begin to use them in a truly mature way—to intentionally study and acquire new information.

The development of memory is both fascinating and fundamental to every other aspect of cognitive growth. It's fascinating because in a very real sense, we are the sum total of what we can remember; memories create the mental continuity that gives each of us a coherent sense of who we are and what we have uniquely experienced. Watching memory dawn in a young child is almost like seeing consciousness gradually emerge out of the fog bank of early experience. Memory development is also critically important, because the brain's enormous capacity to store information is what makes every kind of learning possible. Whether it's bonding with Mother, recognizing Aunt Betsy, mastering crawling, associating words with objects, or figuring out that water is wet, every mental advance depends on the brain's ability to file away experience and then use this stored information to act with greater wisdom and efficiency. Memory is truly the cornerstone of intellectual growth, the brain's sole means of acquiring knowledge, so it is not surprising that even in infancy, it serves as a marker for later intelligence. At the same time, memory flexible skill that can improve with practice. By understanding how the brain's various storage systems develop, we may be able to optimize the several mnemonic skills that are essential to intellectual growth.


The first type of learning to emerge is habituation, the progressive decline in responding that psychologists find so useful for probing babies' minds. Almost as soon as they begin to hear, fetuses habituate to a repeated acoustic stimulus, a loud sound or vibration applied close to the mother's abdomen. Initially, the sound triggers a dramatic startle response—large movements of the baby's limbs or torso that can be observed under ultrasound—but if the stimulus is repeated every twenty seconds, a fetus will respond less and less vigorously until finally he ceases altogether. A few babies show habituation as early as twenty-three weeks of gestation, and by twenty-nine weeks, all healthy fetuses can do it.


Habituation is not the only form of learning that babies exhibit before birth. The same fetal reflexes have also been shown to adapt by a process known as classical conditioning, a learned association between stimuli. Most of us learned in school about Pavlov's famous discovery—that dogs will begin to salivate to the sound of a bell if they have repeatedly heard it rung with the delivery of food. A human fetus can similarly learn after repeated pairings that a sound will signal a vibratory stimulus or, perhaps more meaningfully, that a brief clip of music will relax its mother. In the latter case. pregnant women were asked to consciously relax whenever they heard a particular piece of music, say, Beethoven's Moonlight Sonata. As any pregnant woman knows, fetuses are most active when their mothers are the most relaxed, but the mothers in this experiment soon noticed their babies beginning to move to the music alone, even before they had a chance to relax themselves. Then, after birth, the same music was found to have an especially calming effect on the babies. Classical conditioning has been reported in fetuses as early as five and a half months of gestation and remains an important form of learning throughout life.


The best-studied operant procedure is so simple, and babies enjoy it so much, that you might want to try it with your own child. It is called mobile conditioning. A young baby, like bright-eyed three-month-old Robert, is laid in a crib, facing up at an attractive mobile of five dangling, brightly colored blocks. The mobile itself is pretty exciting, but it gets even better after the experimenter ties a ribbon around one of Robert's ankles and attaches the other end to the mobile's crossbar. Suddenly, Robert is kicking two or three times more frequently than before the ribbon was attached (established as the baseline period). He has discovered that he can actually move the mobile by moving his leg and is simply delighted at this newfound power.

This is the learning phase of the experiment. Memory-testing comes later, when the mobile is reinstalled in his crib but not connected to his foot. Though he hasn't seen it for three days, Robert starts kicking as soon as he sees the mobile, showing that he remembers, at some level in his nervous system, that this behavior will prove rewarding. (It won't, of course, since there is no ribbon this time, so this phase of the experiment can extinguish his increased kicking if allowed to continue more than a couple of minutes.)

Babies as young as two months of age can learn to move the mobile and remember how to do it for a day or two. Between two and six months, they master the task more and more quickly and also remember it for longer and longer periods; three-month-olds remember up to a week and six-month-olds remember up to two weeks after a single training session. They also steadily improve in the amount of detail they can remember. For instance, if the mobile is changed in some way—say, by replacing the blocks with five balls—^Robert will still kick to get it moving. By six months of age, though, he is much more particular and won't kick at the accelerated rate to anything but the identical mobile he trained on. He won't even kick if his crib is moved to a different room or if its distinctive bumper is replaced by another pattern. The fact that young babies are sensitive to the exact environment or context in which they learn something is quite remarkable and shows that they learn not only how to obtain a reward but where certain actions will be reinforced, like rooting for milk only in their mothers' arms, or smiling only when making eye contact.


The first paragraph in this passage outlines the development milestones, while the second is included for its eloquence. Then select passages on habituation, classical and operant conditioning are included as types of memory.

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 What's Going on in There? : How the Brain and Mind Develop in the First Five Years of Life
Books, Brochures, and Chapters>Book:  Eliot , Lise (2000-10-03), What's Going on in There? : How the Brain and Mind Develop in the First Five Years of Life, Bantam, Retrieved on 2011-07-18
Folksonomies: parenting babies development infants physiology