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The phenomenon of the rich getting richer and the poor getting poorer is known as the Matthew Effect. The term, coined in 1968 by the sociologist Robert K. Merton, takes its name from the parable of talents in the Gospel of Matthew. People who are already at the top, the theory says, tend to accumulate more advantage over time and further distance themselves from the rest of the pack.

The Matthew Effect shows up in a range of domains, including in the development of language skills in children. And, within the language-skill domain, the phenomenon is well-reported in vocabulary acquisition. In other words, if you have a rich, extensive, robust, well-endowed vocabulary, then your vocabulary will expand at a faster rate than those who start out with a more limited knowledge of words. And, in a new review paper, UK psychologists point out a Matthew Effect in the memory enhancement associated with "sleeping on it." The paper doesn't present new research about sleep or language skills, but it does reframe existing findings in an interesting way. 

Why do Matthew effects emerge in learning? According to study authors, Matthew-centric studies tend to focus on language exposure as the driving force behind the phenomenon. I.e., kids with strong language skills enjoy reading. So they do it on their own time and pick up new words along the way. But researchers say it's possible that the neurocognitive processes underlying memory play a role in the way exposure and knowledge reinforce each other. This is where sleep comes in. Because the process of converting newly learned information into longterm memories, called sleep-dependent memory consolidation, largely happens during deep sleep.

In general, sleep improves retention of facts. But — but — research has shown that "sleeping on it" helps people lock in information better in some circumstances than in others. When it comes to vocabulary expansion, people seem to learn new words more easily if they already have a base of relevant knowledge. (Here's a post about the selective benefits of sleeping to learn.) Most neuroscience studies on sleep and word-learning have involved adults. But researchers say it's reasonable to apply these findings to smaller, spongier-brained humans. 

Overall, the science on sleep and memory consolidation, researchers write, "points towards an additional means by which children with good vocabulary knowledge could advance at a faster rate than those with poorer vocabulary...suggesting that such effects could be a product of internal learning mechanisms as well as the environmental factors typically considered in previous research."

Understanding the role of memory in vocabulary acquisition, researchers explain, could have a real-world impact. If enhanced slow-wave sleep during childhood facilitates memory consolidation, as researchers believe, then capitalizing on sleep might be a way to help kids with less developed language skills catch up. 

But at this point, researchers have only analyzed existing data. The next step is to run experiments to see how sleep affects acquisition of new words for kids with different levels of knowledge. It's important to include children who have difficulty with language comprehension. They tend to learn at the same rate as other kids initially but slow down afterwards.