Early language exposure affects language processing

Adults typically know thousands of words in whatever languages they know, and can recognize and produce them instantly with very little effort. That means our mental dictionary, or lexicon, has to be organized really well to quickly pull these words from long term memory. One way the lexicon is organized is by what they mean, and it can also be organized by how they are pronounced.

We have done a series of studies asking: 1) Is the organization of the lexicon is the same for sign languages, which are pronounced with the hands and body rather than the vocal tract? and 2) Where does this organization system comes from in the first place, and does language deprivation change it?

Phonology: What 'pronunciation' means for a sign

The whole story turns on one piece of background. Signs, like spoken words, are built from smaller parts. A spoken word is a string of sounds. A sign is a combination of a handshape, a place on the body, and a movement. The forms of words/signs is called "phonology."

Studies of spoken language learning and processing have consistently shown that phonology is one of the ways we organize our mental lexicons. As a person is listening to a word, they start searching for words that start with the incoming sounds.

While signs also have phonology, it doesn't unfold sound by sound the way words do. The handshape, location, movement all are produced at about the same time. That might have consequences for how people recognize, produce, and learn signs.

Do signers organize the lexicon by phonology?

The short answer is yes, and the mind does it automatically, without being asked.

In one of our studies, we shows fluent signers some real signs and some made up signs, and asked them to decide if this a real ASL sign or a made-up one. Signs that have many look-alike phonological neighbors ("ryming" signs) took longer to recognize than signs with few, even though no neighboring rhymes are anywhere in sight.

In one of our studies, we showed fluent signers a mix of real signs and made-up ones and asked them to decide, as fast as they could, whether each was a real ASL sign. Signs with many look-alike phonological neighbors — call them "rhyming" signs — took longer to accept than signs with few, even though none of those rhyming signs were anywhere on the screen. The only way that happens is if the mind pulls up the neighbors on its own.

We have also watched this unfold in real time. When we track signers' eyes as a sign comes in, deaf adults who grew up with ASL start breaking the sign into its parts before it's even finished. A look-alike sign nearby measurably slows them down and pulls their gaze. So people don't wait until they've seen the whole sign to start recognizing it — they begin right away, and they do it by breaking the sign into smaller pieces of phonology.

This pattern shows up early. Using the same eye-tracking experiment with deaf children, we find that children as young as four already treat signs as built from parts: when a child picks the wrong picture, it's almost always a look-alike sign, not a random one.

Finding the same pattern in signed and spoken language is telling. Despite dramatic differences in how signs and words are produced, people use phonology in similar ways to recognize them, which suggests this way of organizing the lexicon is a general feature of how the human mind handles language, not a quirk of speech.

Does language deprivation change that?

Decades ago, researchers noticed that deaf adults who got their first language late tended to get stuck moving from a sign's form to its meaning. They could see the sign but were slower to break it into parts and use those parts to reach the word. Rachel Mayberry and Susan Fischer called it a phonological bottleneck. We've run several studies to understand how that bottleneck comes to be.

Deaf adults who first got ASL later in childhood still recognize signs quickly, but a look-alike sign doesn't slow them down the automatic way it does for signers who grew up with ASL. Late signers leaned more on a sign's meaning, and their sensitivity to its form showed up only later, after the sign had fully played out, like a double-check. This fits a broader pattern. Severely limited language access in early childhood leaves a lasting mark on how adult signers process the form of signs, which shows up across many different kinds of experimental tasks similarity judgments, brain imaging, lexical decision, priming, and sentence processing.

Early access to language helps the brain process both the form and meaning of words efficiently."​

Early access to language helps the brain build a lexicon that processes both form and meaning quickly and automatically.

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