The average person of a 21-year-old knows about 27,000 to 52,000 different words. At age 60, that number averages between 35,000 and 56,000. When pronounced aloud, most of these words last less than a second. So the brain has a quick decision with every word. to do: Which of these thousands of options matches the signal? About 98% of the time, the brain chooses the right word.

But how? Language comprehension is distinct from reading comprehension but is similar to sign language comprehension, although spoken word recognition has been studied more than sign language. Key to our ability to understand language is the brain's role as a parallel processor, meaning it can do several different things at the same time. 

Most studies believe that each word we know is processed by a separate processing unit that has a single task: assessing the likelihood that incoming speech will match that particular word. In the context of the brain, the processing unit that a word represents is likely a pattern of activity firing across a group of neurons in the cerebral cortex. 

When we hear the beginning of a word, several thousand of these units can be activated because there are so many possible matches just by matching the beginning of a word. Then, as the word progresses, more and more units register that some vital information is missing and lose activity. Possibly long before the end of the word, only one trigger pattern corresponding to a word remains active.

This is called the "reconnaissance point". When refining a word,  active units suppress the activity of others, saving vital milliseconds. Most people can understand up to  8 syllables per second. However, the goal is not only to recognize the word but also to access its stored meaning. 

The brain accesses many possible meanings simultaneously before the word is fully identified. This is known from different studies that show that even upon hearing a word fragment like "jet," listeners begin to register multiple possible meanings like captain or capital before the full word comes up. This suggests that every time we hear a word, there is a brief explosion of meaning in our head and at the point of recognizing the brain has locked into an interpretation. The recognition process is faster with a sentence that gives us context than with a random string of words. 

The context also helps us to find the intended meaning of words with multiple interpretations like "bat" or "crane" or in cases of homophones like "not" or "white". For multilingual people, the language is their hearing is another signal used to eliminate potential words that do not fit the context of the language.

So how about we add entirely new words to this system? Even as adults, we might come across a new word every few days. to overwrite the old ones? We believe that to avoid this problem, new words are first stored in a part of the brain called the hippocampus, which is far from the main storage of words in the cortex, so they don't share neurons with other words. 

Then, over several nights of sleep, the new words are gradually transmitted and intertwined with the old ones. Researchers believe this gradual acquisition process helps avoid the disruption of existing words. Therefore, during the day, unconscious activities create bursts of meaning as we speak. At night we rest, but our brain is busy integrating new knowledge into the vocabulary. When we wake up, this process ensures we are ready for the ever-changing world of language.


Reference:

1. How do our brains process speech?

2. How Speech Is Processed In The Brain

3. Wu Dao 2.0 – Bigger, Stronger And Faster AI From China