Moved by Bruce Willis’s family’s announcement that he is leaving acting after being diagnosed with aphasia, we revisited language disorders and the kinds of things we can learn from them.
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Language impairment is often caused by tragic conditions like aphasia, a type of brain damage. This condition can teach us a lot about how language works. To begin to understand such a complex, fascinating and ever-changing field, we will first talk about the human brain and the field devoted to its study.
What Is Neurolinguistics?
Neurolinguistics is a branch of neuroscience whose goal is to understand the neural aspects of language, such as how the brain processes language. To do research in neurolinguistics, neuroscientists depend largely on impaired language data, not normal language data. In other words, analyzing the patterns in the abnormal speech of someone who has suffered from an event like a stroke or from someone who has a medical condition like dementia, provides information for scientists that normal speech cannot provide.
The Basic Components of Our Brains
The brain consists of more than 100 billion nerve cells—called “neurons”—which are connected with fibers. The brain’s surface is called the cortex, or “gray matter,” and is responsible for making decisions, storing memories, initiating action, and, of course, for our knowledge of language and grammar. One of the coolest things about the brain is how it’s wrinkled and folded up, because if it weren’t, our heads would be enormous! The cortex is thin, but quite large in surface area, and we need for all of that surface area somehow to fit into the skull—it’s like taking a sheet of newspaper and crumpling it into a ball to fit inside a small bowl. In proportion to our bodies, human brains are larger and more intricate than any other living creature.
You may have learned that the brain has two halves, which are known as its hemispheres (“hemi” is a prefix that means “half”). They are connected by the “corpus callosum”—a network of 200 million fibers. Incredibly, some patients with severe epilepsy need to have this connection surgically removed, and they are still able to function normally! You may also have heard that brain function is “contralateral,” which means that the left side of the brain controls the right side of the body, and vice versa.
Lots of Language Processing Happens in the Left Side of the Brain
The answer to this question is complicated. You may have heard that the left hemisphere is “responsible for language,” and that is mostly true: It’s called “lateralization” when a brain function is localized to one hemisphere (“lateral” means “side”).
Scientists have figured this out using technology such as CT scans and PET scans, which show the areas of the brain that light up when subjects are given various types of language stimuli, and the areas that light up when they get non-linguistic stimuli, too.
Furthermore, those epileptic patients with the separated-hemisphere surgery provide a dramatic illustration of this language-on-the-left idea, because although those patients function just fine after the operation, controlled experiments show that separating the hemispheres results in some odd language changes.
For example, one experiment blindfolded the patients, and placed simple objects like keys and pens into one hand at a time. These subjects were able to easily name objects in their right hand, because the left hemisphere—where language is located—operates the right hand. However, in the left hand, they recognized the objects but were unable to name them, because the right hemisphere operates the left hand, but does not process language, and more importantly, they are blindfolded, and their right hemispheres can no longer communicate with their left hemispheres!
Language Isn’t Limited to the Left Side of the Brain Though
So, it seems pretty clear that language lives on the left side of our brains, right? Well, it’s not that simple. Research, including that same brain-scan research, shows that small amounts of language processing are found in the right side of the brain, too, and that the amount varies from person to person. Remarkably, left-handed people are less lateralized for language, in that they have significant language representation in both of their hemispheres. Left-handed people also recover from language loss after strokes better than right-handed people because they have language spread out more evenly. In fact, this quicker recovery is also observed in right-handed people who have left-handed people in their family!
Let’s back up: Despite the fact that the hemispheres of the brain do a lot of work in concert with each other, there absolutely is a general tendency for language to lateralize left, and the details of this tendency are very interesting. The history of neurolinguistics explains a lot about these basic facts, starting with Paul Broca, a French surgeon from the 1800s, who noticed language problems in patients who had experienced trauma to the front left portion of the head, near the temple. This area of the brain is now known as “Broca’s area.”
Around 10 years later, a German neurologist named Carl Wernicke noticed that his language-impaired patients had lesions in the left temporal area, which is the same left hemisphere but farther back. (Back then, the discovery could only occur during autopsies, of course.) This part of the left hemisphere, like a neighbor to Broca’s area, is now known as “Wernicke’s area.”
What Is Aphasia?
Aphasia is any disease- or trauma-induced brain damage that causes a language disorder. Though most commonly caused by stroke, it can also be caused by infection, tumors, hemorrhaging and blows to the head. The worst type is called “global aphasia,” which causes the patient to be mute.
Less severe types of aphasia, when some language is retained, are commonly split into two types called “fluent aphasia” and “non-fluent aphasia.”
Fluent aphasics speak fluidly, as the name implies, but they may not make sense when they speak.
Non-fluent aphasics produce labored speech, and have difficulty structuring their sentences, but their messages are more understandable. (We’ll see some examples of these utterance types shortly.) In addition, the labored speech in the non-fluent type is usually “agrammatic,” which means it lacks functional elements of language such as prepositions, articles, and pronouns. Function words are also called closed-class words, because the closed classes don’t gain new members very quickly. So, people with non-fluent aphasia often form sentences without prepositions, articles and pronouns, and struggle to get the utterances out. However, they have an easier time with content words like nouns, verbs and adjectives. Content words are also called open-class words, because they gain new members all the time! For a review of this fun language distinction, read Part II of the series “Why Do People Say ‘A-Whole-Nother’?
When people develop language disorders, it is devastating to them and to their loved ones. However, from a scientific perspective, the process of attempting to understand the disorders, and develop treatments, has provided us with vast amounts of information about how language works in a general sense. For example, we know that this linguistic distinction between function words and content words is not just something that linguists made up or imagined. Why? Because much of the non-fluent aphasia—the one that causes agrammatic speech—is classified as “Broca’s aphasia” because it is caused by damage to Broca’s area.
Here is an example of an utterance produced by a Broca’s sufferer, documented by linguist Victoria Fromkin. It was in response to the patient being asked if he had been going home on weekends:
Why, yes…. Thursday uh… uh… uh… no… Friday… Bar…ba…ra…wife… and oh car… drive… you know… rest… and TV.
Now here is an example of how Broca’s aphasia affects the sufferers’ ability to understand those grammatical components of language. Sentence can be harder for Broca’s aphasics to understand than sentence:
The cat was chased by the dog.
The car was chased by the dog.
Sentence requires knowledge of syntax in order to be interpreted because the sentence is in the passive voice, whose word order is not the more common English order. (By the way, the “more common” English order, which is “subject + verb + object,” like “The cheetah ate the cake,” is called “canonical.”) So, imagine a sufferer who is lacking the ability to process those functional language pieces, such as the “-ed” past tense verb ending (that’s called a bound morpheme—read more about those here), and the preposition “by.” Even the verb “was” is a function word because it is an auxiliary verb, not a main verb.
So, when aphasics can only process content words, like “cat,” “chase” and “dog,” they are less likely to correctly process the doer and the receiver of the chasing action in sentence. That’s because if you strip the sentence down to content words, it might be “cat chase dog,” so the person with Broca’s aphasia may be misled, and say that the cat must be doing the chasing, because canonical word order in English is the most common and straightforward.
However, sentence has stronger semantic information (again, that means “meaning”): Cars are not animate, and cannot really chase things, so these aphasics may more aptly ascertain/guess that the car is the recipient of the chasing action, even with the tricky word order.
Whether something is animate or not is one of the many features that are encoded within every word that we learn in the languages we know. In other words, in sentence, semantics does not provide enough information, because both cats and dogs can be chasers, and this would be difficult for a speaker who is dependent on semantic knowledge, due to having suffered grammar loss.
A final example of this function/content distinction, which is both fascinating and sad, is the nature of the dyslexia that aphasics often acquire along with the spoken-language loss. In reading tests, because of their difficulty with function words, Broca’s patients are unable to read function words out loud from test cards, yet they can read homophones—those are words that sound the same but mean something else—if the homophone is a content word! For example, a patient may read the word witch without a problem, because witch is a content word. It is a noun that you can define, and picture in your mind. However, this same patient may struggle immensely to read the homophone which, because which is a relative pronoun: a grammatical, closed-class word.
Now, let’s talk about damage to Wernicke’s area of the brain. The resulting Wernicke’s aphasia is a type of the fluent aphasia, which means that the speech is not labored, and the sufferers are still able to use function words like articles and prepositions. Their words most often occur in a grammatically correct order (remember, this type is not “agrammatic,” like Broca’s aphasia). Instead, they have trouble with picking the right content words. So, the Wernicke’s sufferers may use one content word when they need another, but they speak at a normal pace. They tend to produce meaningless utterances and they also, unfortunately, tend not to be able to understand what is spoken to them, so meaning is impaired for them in a very general sense. Noam Chomsky, the “grandfather” of linguistics, created the following sentence to show that in human language, meaning is separate from syntax/word order:
“Colorless green ideas sleep furiously.”
This sentence sounds a bit like something that someone with Wernicke’s aphasia could say. It is grammatically correct, in that the word order follows syntactic rules, and, for example, the subject-verb agreement is correct for most English dialects, but it makes no logical sense at all.
In addition to this, some Wernicke’s aphasics produce nonsense words—those are words that could be English, phonologically, but aren’t, such as, say, “fripple.” Some substitute a word that rhymes with the word they want, like “tire” for “fire.” Sometimes, they produce words that are semantically related to the word they want, like “banana” for “apple.”
One other interesting thing that this tells us about the brain is that words do not seem to be stored in a list, but rather, in neural networks or clusters. Imagine a network in which “pool” is stored in the brain close to “water,” “swim,” “dive,” “wet,” “blue” and many others, yet the word also has a neural link to “tool,” “fool” and “drool,” due to shared phonological properties. This concept is illustrated by the errors produced by patients who suffer from language loss. In fact, you may notice that it is illustrated by your own everyday slips-of-the-tongue, too!
To wrap up the definition of Wernicke’s aphasia, here is a sample patient utterance, also documented by linguist Victoria Fromkin:
The only thing I can say again is madder or modder fish sudden fishing sewed into the accident to miss in the purdles.
While we can’t make sense of this, notice how the sufferer uses function words like the infinitive “to” correctly, and includes a past tense ending on the verb “sew,” etc. This example also shows no hesitation, and finally, it illustrates some Wernicke-type nonsense words, like “modder” and “purdles” (which may be a substitute for “puddles”).
Damage to the Language Areas of the Brain Reveals Facts about Grammar
In summary, because brain scans show damage to the areas that correspond to the types of aphasia that the patients suffer from, the contrast between these two types of aphasia shows us that not only is language (mostly!) lateralized to the left hemisphere, but also that major language components reside in distinct portions of the brain that are designated for them: One is linguistic grammar, meaning word order and function words, which is found in Broca’s area, and the other is linguistic meaning, meaning semantics and content words, which is found in Wernicke’s area.
By the way, this distinction between content and function is one that all languages have, and also, it is a distinction that linguists refer to as a “psychological reality.” That means that even people who have never heard of it may observe it unconsciously, and even joke about it. Here is a funny scene from The Office, in which Kevin drops the functional language from his speech. He says things like “stop worry!” in a futile and comical attempt to “save time.” Here is a funny scene from Friends, in which Phoebe and Rachel fight over who gets which alternating words on their outgoing voicemail message. They literally designate an expression for content words! They call them “the good words.” Phoebe gets mad because she is stuck with “it’s,” “a,” “and,” etc., while Rachel gets “Phoebe,” “Rachel,” “leave,” etc.
You may also notice that children in their earliest stages of language development produce abbreviated sentences that are missing those functional pieces. Linguists compare this developmental stage to the genre of language that people used to write telegrams years ago, which had low character limits. Missing articles and prepositions saved space, but allowed the message to come through, not unlike Broca’s aphasia.
A final language concept that we can take away from all of this information about language impairment is the overwhelming evidence that the brain is modular, which means it is compartmentalized into specialized sections. Aphasia symptoms have no relationship to any loss in motor skills, intellectual abilities, hearing, or physical impairment of language articulators like the tongue or vocal cords. Plus, aphasia in deaf people is extremely similar, because signed languages are as equally complex and sophisticated as spoken languages. So, this indicates that language is what gets lateralized and localized, not speech, and language resides in the mind.
We can end with the caveat that aphasia is very complex, and you may have known people who had aphasia but illustrated different symptoms than we had room for today. For instance, some non-fluent aphasics develop “dysprosody,” which means they lose some intonation, and speak more monotone than is normal. Some aphasics simultaneously develop actual speech production impairment, which leads them to struggle with pronunciation, such as reducing consonant clusters like “spoon” to “poon.” Errors like that are called “phonemic paraphasias.”
Some patients are able to recover from aphasia with speech therapy, and some are not. Some research on the general difficulty with naming and defining objects or concepts, called “anomia,” observes that it occurs in both types of aphasia described in this article, while some research classifies it as a separate type, called “anomic aphasia.”
Another twist is that many patients start off with non-fluent aphasia, but progress to a more fluent form with recovery time. There are even other, lesser-known areas of the brain, such as Brodmann’s, that can affect language when damaged. Some patients may retain the ability to understand both spoken and written language, but lose the ability to speak or write themselves.
You may have known people with age-related dementia who forget words and names, but this condition is more of a cognitive than linguistic deficit, and affects different parts of the brain from aphasia, despite sharing many symptomatic similarities.
So, there are many variables, and it all depends on the patient, on what parts of the brain are subjected to the damage, and on which nonlinguistic brain components are damaged along with the linguistic ones.
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