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March 6, 2021

Vocabulary learning is possible during sleep

By ALLISON CHEN | February 14, 2019

Those who have always dreamed of being a little more productive during sleep are in luck. A group of researchers at the University of Bern in Switzerland have recently demonstrated that individuals can indeed learn new words while sleeping. Their findings were reported in a university media release.

Prior research on this topic had primarily focused on the role sleep plays in consolidating information people gain when they are awake, and the public was skeptical of the idea that humans could learn new information while they were asleep. 

Some studies had shown that humans are able to process subliminal, or “consciously invisible” stimuli when awake; however, relating this to abilities during sleep was tenuous. 

Hypothesizing that learning during sleep would probably work only during limited periods of time, the Swiss researchers focused their attention on slow-wave peaks, during which the neural network bears the greatest resemblance to its state when awake. 

Participants in the study, all of whom were young and native German speakers, were played pairs of words while napping. 

One word in the pair was a made-up foreign word — “tofer,” for example — while the other word was a real German word — “Haus (house),” for example. 

The pairs were repeated four times in a row, and the order the words were played in was switched each time. 

Once the participants woke up, they were shown the fake words and asked to determine whether the noun represented by the word would fit into a certain shoebox. 

The researchers found that the participants answered correctly more often than would be expected from guessing.  

While the participants were sleeping, an electroencephalogram (EEG) was used to consistently track the electrical activity in their brains. 

The recordings showed a series of frontal slow-wave peaks after the researchers played the first word, with the second peak often corresponding to the timing of the second word. 

By comparing EEG data to the participants’ correct and incorrect answers, the researchers found that if the second peak occurred shortly before the second word was played, and lasted longer, the participant was more likely to answer correctly later when shown the fake word in that pair. 

In order for participants to learn the word, the second peak had to have preferable timing and characteristics at least two out of the four times each word pair was played. 

In addition, the researchers found that if the second word was played during a slow-wave trough, the participant’s ability to learn or retrieve the word was negatively impacted. 

In fact, the researchers showed that the second word of a pair occurred during a trough two or more times, participants answered correctly at a rate less than that which would be expected from guessing.

The researchers further noted that the timing of the first word was unimportant. Whether the first word occurred during a peak or a trough did not ultimately affect participants’ ability to correctly retrieve the fake word from that pair.

While the participants were being tested after their nap, the researchers recorded fMRI data. 

Through the data, they soon discovered that the hippocampus and the visual word form area (VWFA), which are typically believed to be involved in the association of words with images, both showed signal increases when participants answered correctly. 

These regions are involved in learning new vocabulary when awake.  

Marc Züst, an author of the paper, summarized his team’s findings in a press release. 

“These brain structures appear to mediate memory formation independently of the prevailing state of consciousness,” Züst said in the press release.

The researchers further determined that the participants’ level of tiredness before the nap did not affect how well they learned words. 

They also determined that size semantics, or the association of sounds of the fake words with certain meanings, was not a cause of the results they observed.

The authors of the study anticipate that there will be more research into learning during deep sleep in the coming years. 

Sleep research is a psychological area of study that has always been relatively unnoticed in the past years. 

However, as more research continues to shed light on the topic, the new insight that will potentially be gained about the human sleep cycle is limitless. 

Some of it will likely upturn more of our notions about our capabilities during sleep, as these current findings had already proven. 

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