As I’ve mentioned before, research into childhood development is tricky, thanks to ethical and practical constraints on what researchers can do. Consider randomized controlled experimental studies – that is, taking a group of test subjects, dividing them at random into a group that receives some sort of experimenter-determined influence and a group that does not, and noting the differences between the two groups after. This is considered the gold standard for making causal inferences, and it is the way that, for example, we test the efficacy of drugs that are in development.
But there are obvious constraints. For one, ethics prevents us from deliberately causing harm; you can’t apply the condition of abuse or malnutrition to children, of course. But we remain interested in how these conditions affect development. There are also practical constraints. Even aside from ethical reasons, we have no way to randomly assign dyslexia or aphasia to people. More pragmatically, in educational research we often can’t randomly assign condition to individual students in a class setting. It’s simply not feasible or fair to ask a teacher to give, say, 7 students one lesson plan and 13 students another in the same class setting. Typically we instead assign condition to classes rather than individuals – Class A doing the conventional lesson plan (control) and Class B a new one (test). But there are issues with alpha and statistical inference there, though we can address them with things like hierarchical linear models and other types of nested models.
One of the places where research constraints have significantly limited out ability to investigate core developmental questions lies in language acquisition. The degree to which language is learned vs. acquired – indeed, what that distinction even means – remains somewhat unsettled. So does the question of a “critical period,” the idea that there is a time in the life cycle when children’s brains are particularly attuned to acquiring language. We have developed this intuition, in part, from the sturdy observation that children seem to be better able to acquire (learn?) a second language than adults, particularly when in an immersive environment. But conclusive proof of the existence of the critical period remains elusive, in part because we have limited ability to study what happens when children grow up in unusually linguistically poor environments. Given that we can’t go out of our way to stunt the language development of test subjects, for obvious reasons, we often have to turn to “natural experiments” – that is, situations where circumstances have conspired to create something like a natural assignment to condition. There’s all sorts of complicated epistemological questions in these cases, but they are often the best we can do give constraints.
Today’s Study of the Week concerns the development of language and just how powerful the human language instinct is, through one of the most fascinating natural experiments I’ve ever read about: the story of Nicaraguan Sign Language.
The Poverty of the Stimulus
Modern syntax has a kind of communal origin story, and like so many other aspects of linguistics, that origin story comes back to Noam Chomsky.
Chomsky famously rewrote the study of language, placing theoretical syntax at the fore of the field and declaring the study of language to be fundamentally part of cognitive science. Since at least Ferdinand de Saussure, the emphasis on mental structures (as opposed to exploring the development and “meaning” of arbitrary phonological shapes of particular words in particular languages) has been core to linguistics, but Chomsky took this work further than anyone, leading to a state where Chomsky acolyte Akeel Bilgrami could write in a 2015 book,
[The theory of language] is not a theory about external utterances, nor is it, therefore, about a social phenomenon. The nomenclature to capture this latter distinction between what is individual/internal/intensional and what is externalized/social is I-languages and E-languages respectively. It is I-languages alone that can be the subject of scientific study, not E-languages.
This is High Chomskyanism at its most frustrating, as I’ve written about before, but for our purposes will suffice to define his project. And this focus on the interior, cognitive dimensions of language is intimately connected to a central concept of Chomsky’s approach: the notion that the language capacity is a part of our genetic endowment, and that learning language is therefore fundamentally different from learning algebra or how to skip a rock. It was this contention that led to a book review which helped to make Chomsky’s reputation and which is part of the origin story of modern linguistics I mentioned above.
The book in question was written by BF Skinner, then the most famous and influential mind in psychology and human development. Skinner’s ideas – still prominent in parts of human psychology and especially in animal behaviorism – were centered on the idea of conditioning, the notion that behavior is the product of external systems of reward. Pavlov’s dog salivated when it heard a bell ring because it had been conditioned to associate that bell with a food reward; a neglected child throws tantrums because she has be conditioned to see doing so as the only way to get the reward of attention. In basic terms we can still see the truth of this essential insight, that behaviors that are rewarded tend to be repeated.
But Skinner, like a lot of great minds, over-generalized his most famous theory, seeking to push it into more and more domains. In particular, he wrote a book called Verbal Behavior, published in 1957, that sought to explain language acquisition through behaviorist principles. A child cries in a particular way, his mother learns that this cry means “I’m hungry,” and he is rewarded for communicating. As he grows, he makes more and more sophisticated sounds, modeling the words he hears around him, and is similarly rewarded. Eventually he develops adult language capacity through stimulus and reward.
Chomsky wrote a famous, famously scathing review of Skinner’s book. I suspect that the review has become somewhat overemphasized in the story of Chomsky and how he came to dominate contemporary linguistics, but there’s no question that it was a prominent early moment for his theories, or that taking on the old guard in that way was highly symbolic. Central to Chomsky’s critique was the concept of the “poverty of the stimulus.” The poverty of the stimulus argument depends on a simple observation: what even very young users of language can accomplish with language far exceeds what they’ve been exposed to. That is, the stimulus (their observations of the language use of others) is insufficient (impoverished) as an explanation for what they can do. The average five year old is perfectly capable of combining words and phrases in such a way that they produce a sentence that has never before been uttered in the history of the world. Language is made up of discrete parts that humans arrange into meaningful expressions without consciously controlling them, and the implicit rules through which we do this arranging are the natural subject of linguistic study. Or say say the followers of Chomsky.
Chomsky used the poverty of the stimulus theory as indirect evidence for the notion of a genetic language capacity, something unique to the human genome that gives us the ability to master the incredible complexity of real grammars without ever being formally trained in their use. (You don’t, I hope, sit there showing your 6 month old flash cards of the parts of speech.) Rather than arriving at language tabula rasa and acquiring it through the kind of rote practice that you learn to tie a tie, you “learn language in a way a bird learns wings,” as he once put it. We are the language-using animal, and this is the product of evolution and not of culture.
Where exactly this language capacity resides in the brain, and where the language instinct can be found in the genome, remain unanswered questions. And as with any prominent theory there are detractors and skeptics. The inability to conduct an experimental study to see how linguistic deprivation might influence the acquisition of language complicates our ability to sort these questions. But in the late 1970s, the government of Nicaragua inadvertently provided us with clues.
Nicaraguan Sign Language: the Language of the Truly Stimulus-Impoverished
For much of the history of the Nicaraguan state, deaf children had essentially no formal support from the government. As has been sadly typical in the history of children with disabilities, deaf Nicaraguan children were often socially isolated, kept at home away from peers and the greater community, typically lacking any formal education at all. Obviously, lacking the ability to hear and often to speak, and never being taught any kind of formal sign language, these children faced enormous obstacles to communicating effectively.
But in the late 1970s, a part of a broader set of social reforms, the government opened an elementary school for children with disabilities. Later on they would found a similarly-focused vocational school. For the first time, these communicatively-deprived children were granted the opportunity to interact with peers and learn in a formal setting. But they were still not granted the chance to be fully-functioning communicators. The school administrators had decided, for whatever reason, to restrict the students to signing – letter by letter – in Spanish, rather than teaching them a mature sign language. The communicative insufficiency of this should be obvious. Try speaking to someone you know by spelling out each word by the letter and you’ll see what I mean. So the kids took matters into their own hands: they generated their own human language.
Within a few years, a complex and robust language, Nicaraguan Sign Language (NSL), had been born. It has been passed down through generations of deaf Nicaraguan children, advancing and evolving quickly as it does. In time, researchers realized what this represented – a natural experiment on the linguistic capacities held by children who faced enormous disadvantages, and the chance to watch the birth of a new language in real time.
The story has been told in several places, but today I encourage you to read a 2004 study in Science on NSL. The study, by Ann Senghas, Sotaro Kita, and Asli Ozyurek, uses NSL to consider how languages develop over time. In particular, they use signs for types of motion to show how a language develops the ability to talk in greater abstraction and thus becomes more sophisticated and flexible. Why motion? Think about the nature of signing. If I want to get the concept of a wave across to you, I would naturally tend to make a wave with my hand, as remains the sign for wave in American Sign Language. But note that communicating iconically – that is, by matching something about the thing being referred to with something in the sign you’re using to refer to it – is in the broader sense unsophisticated or insufficient. What functioning languages must do is present the opportunity for abstraction and segmentation. Pictographic languages, where words are images of the things they stand for, are primitive because they prevent us from moving from those specifics to more general ideas. Instead, mature languages combine several key properties that make them flexible and useful:
We focus here on two particular properties of language: discreteness and combinatorial patterning. Every language consists of a finite set of recombinable parts. These basic elements are perceived categorically, not continuously, and are organized in a principled, hierarchical fashion. For example, we have discrete sounds that are combined to form words, that are combined to form phrases, and then sentences, and so on. Even those aspects of the world that are experienced as continuous and holistic are represented with language that is discrete and combinatorial. Together, these properties make it possible to generate an infinite number of expressions with a finite system.
The researchers therefore were interested in seeing how these properties were developing in NSL. So they divided their participants into different cohorts of aptitude and fluency in NSL, to see how much more abstracted the motion signs of the advanced NSL users might be. They found that in fact the more advanced cohort was significantly more likely to use the type of discrete patterning described above. That is, the more sophisticated speakers were, the more abstracted their description of motion was even though motion signs can be easily understood outside of a sign language context – and despite the fact that there are trade offs here:
Note that this change to the language, in the short term, entails a loss of information. When representations express manner and path separately, it is no longer iconically clear that the two aspects of movement occurred simultaneously, within a single event. For example, roll followed by downward might have instead referred to two separate events, meaning “rolling, then descending.” However, the communicative power gained by combining elements more than offsets this potential for ambiguity
This is essentially the deal that we make – that our brains make – as we develop more sophisticated languages. We trade simplicity (a picture of a sun for a system of sounds/letters that can be broken apart and assembled into a combination that conveys the abstracted idea “the sun”) for the capacity for complexity and abstraction. Given that many have argued that the development of sophisticated languages marks the beginning of humanity’s great intellectual leap forward out of the pre-modern phase and into civilization, this seems like a good trade indeed.
The question of how deeply embedded the language capacity may be in the human genome, and what precisely that capacity determines in terms of rules for how languages work, remain unanswered. Going on 60 years into the Chomsky project, we still don’t have a comprehensive set of “rules” that the genetic language capacity enforces on human expression. But the idea that language is a kind of information that is learned like any other, through conscious absorption and rote practice, seems unsupportable. To explain what these children did, and what humans have done for millennia, it seems inarguable to me that there is some special capacity in the genome for language learning, as surely as there is something in our genome that compels us to walk on two feet.
Wherever the study of human language development goes next, I will always come back to the story of Nicaraguan Sign Language, which has fascinated me for years and which never fails to amaze me even after all that I’ve read about it. This is that story: a group of young deaf children, all of whom suffered from severely reduced exposure to language compared to most children, many or most of whom grew up in poverty, some of whom had various other cognitive and developmental disabilities, spontaneously generated a functioning human grammar despite the immense complexity of such grammar and in the face of adult authorities actively trying to stop them from doing so. That’s the potential of the human language instinct, which functions, as a distributed network, as the most powerful information system in the history of the world. Nothing else, not even the entirety of the internet, comes close.