Quite a bit of research has begun
to explore influences of sleep on
cognitive processes. In adults,
sleep has a huge influence on memory.
Sleep speeds learning of new skills.
It also helps to separate the information being learned from the situation
in which it was learned, which can make it easier to use that knowledge in
other circumstances.
Young children spend a tremendous
amount of time asleep, and so research is also beginning to explore the
influence of sleep on things children learn.
An interesting study in the March/April, 2014 issue of Child Development by Denise Werchan
and Rebecca Gomez examined how sleep influences toddlers’ ability to learn new
words.
When a child learns a new noun,
for example, it is important for the child to be able to apply that word to the
object (or objects) for which they have seen it used, but also to apply that
word to other objects that come from the same category. For example, a child may sit in the family
minivan and hear it called a car. She may see a neighbor’s sedan and hear that
called a car as well. She might also be given a four-wheeled toy
and hear that is a car, too. To be a successful language-user, this child
ultimately has to be able to recognize which other objects should be called a car and which ones should not.
This process requires generalization. That is, the child has to go from the limited
number of instances of the category they have seen to figure out which other
objects share the same label. This
process requires some amount of forgetting.
After all, the child will observe many characteristics of these objects
like their shape, size, color, and parts.
Some of these characteristics (like shape, and some parts) matter a lot
in deciding whether to call something a car, and others (like color) matter less. So, it is helpful for the child to forget
some of what they have seen in order to begin to generalize the new word to
other objects.
Werchan and Gomez suggested that
sleep might actually interfere with toddlers’ ability to learn new words. These researchers argued that sleep helps to
solidify memories, and so if children associate too much information with a
label, they might not learn to generalize it to new objects.
To test this possibility,
30-month-old toddlers were taught labels for three types of novel objects
(which were constructed by the researchers).
The labels were words like dax
or tiv that are not used as words in
English. During the training, children
saw three examples of each object. They were also exposed to several other
novel objects that were not labeled, that would be used as distractors
later.
One group of children was tested
about an hour before their normal nap time.
They napped, and then came to a psychology lab to be tested four hours
after the training. A second group was
tested far from their normal nap time.
They were also tested in the lab four hours after training, but they had
not napped. A third group was trained
and then tested immediately.
During the test, children saw
four objects: a new example from one of the
categories they learned, an object they saw during training that had not been
named, an unfamiliar object, and a familiar object (like a toy duck). They were told the label and were asked to
point to the object. For example, if
they saw the object that had been called a dax
during training, they would be asked “Which one’s a dax? Can you point to the one that’s a dax?”
The children who were tested
immediately and those who napped got about 40% of the test questions
correct. The children who did not nap got
over 80% of the test questions correct.
This study suggests that when
toddlers are learning words, their ability to generalize those words to new
objects requires them to forget some of what they saw. More of this forgetting happens when children
remain awake than when they sleep. So,
this kind of word learning is enhanced when children stay awake after learning
the words.
As the researchers point out,
this finding differs from what is usually observed with adults. Adults often generalize their learning better
after sleep. The difference is that adults
are better than toddlers at focusing on the most important information when
learning something new. So, for adults
the most important part of generalizing is separating the content of what was
learned from the situation in which it was learned. Sleep helps with that separation. Toddlers need to forget some of the content
of what they learned in order to generalize effectively, and so for them sleep
helps them.