neurolengua

Be It Numbers or Words – The Structure of Our Language Remains the Same – Association for Psychological Science.

It is one of the wonders of language: We cannot possibly anticipate or memorize every potential word, phrase, or sentence. Yet we have no trouble constructing and understanding myriads of novel utterances every day. How do we do it? Linguists say we naturally and unconsciously employ abstract rules—syntax.

How abstract is language? What is the nature of these abstract representations?  And do the same rules travel among realms of cognition? A new study exploring these questions—by psychologists Christoph Scheepers, Catherine J. Martin, Andriy Myachykov, Kay Teevan, and Izabela Viskupova of the University of Glasgow, and Patrick Sturt of the University of Edinburgh—makes what Scheepers calls “a striking new finding”: The process of storing and reusing syntax “works across cognitive domains.”

More specifically: “The structure of a math equation correctly solved is preserved in memory and determines the structuring of a subsequent sentence that a person has to complete.” Neuroscientists have found evidence suggesting a link between math and language, “but this is the first time we’ve shown it in a behavioral setup.”

The findings will be published in an upcoming issue of Psychological Science, a journal of the Association for Psychological Science.

The study made use of a cognitive process called structural priming. Simply put, if you use a certain kind of structure in one sentence, you’re likely to use it again in a subsequent sentence. To find out how abstract—and cognitively general—this process is, the experimenters gave native English-speaking students a pencil-and-paper test containing a series of math problems paired with incomplete sentences.

Each math problem was structured in one of three ways. With “high-attachment” syntax, the final operation of the problem applied to a large “chunk” of the earlier part. For instance: 80 – (5 + 15) / 5, where the final division (/ 5) applies to the previous addition term (5 + 15). With “low-attachment” syntax—say, 80 – 5 + 15 / 5—the final operation applied to a smaller previous chunk. A third category—“baseline” problems like 80 – 5 —implied neither high nor low attachment.

After each equation, the participant was given a sentence fragment that could be completed with either high or low attachment syntax. For instance – The tourist guide mentioned the bells of the church that … A high-attachment ending would refer to the entire phrase the bells of the church and might finish with “that chime hourly.” Low attachment would link only the church to the completed final clause—say, “that stands on a hill.”

The subjects were variously successful in solving the problems. Their choice of high or low attachment sentence completions also revealed complexities—some perhaps related to the preference in English for low-attachment syntax.

Still, in significant numbers, high-attachment math problems primed high-attachment sentence completions, and low-attachment problems made low-attachment completions likely.

What does all this mean? Our cognitive processes operate “at a very high level of abstraction,” the authors write. And those abstractions may apply in similar fashion to all kinds of thinking—in numbers, words, or perhaps even music.

One of the most controversial and influential aspects of Chomsky’s legacy is the hypothesis that there is an innate component to language, which he named Universal Grammar (Chomsky 1966), in homage to the rationalist thinkers in whose footsteps he was walking. Here I  discuss results obtained in cognitive science, that bear on this central issue.

I will start by  going back,  and start with a piece of literature that is crucial for understanding what the research program of generative linguistics is, and also what the current research program is in the interdisciplinary study of human language. I am referring to the review that Chomsky wrote of B.F. Skinner’s Verbal Behavior (Chomsky 1959).

The hypothesis that there are innate organism-internal factors that constrain the languages that humans know and use sounded preposterous to most scholars in the Humanities and Social Sciences back in 1959 when Chomsky published it. The universal grammar (UG) hypothesis, as he later named it, has since generated a great amount of research, discussion and argument, a distinguished example of which is the Royaumont Debate between Piaget and Chomsky in 1975. In other fields however, such as Biology, the claim that human languages are largely shaped by innate conditions not only did not encounter resistance, but was received with sympathy, because it naturally converged with a general view of living organisms and the importance of genetic factors in behavior (Piattelli-Palmarini 1994).

I think it safe to say that, fifty years later, it is widely accepted that innate mechanisms have a relevant role to play in a full understanding of the human capacity for language. Current disagreements concern the nature and specificity of those mechanisms, regarding both our species and the cognitive domain(s) where they belong.

So  the question I will pursue is: what are the contents of Univesal Grammar (UG)? That is to say, what has been discovered regarding the innate component of human language since it was argued, half a century ago, to be a significant part of a human’s knowledge of language? I will not engage in an exhaustive review of the variety of linguistic arguments and evidences put forward during these years to substantiate the hypothesis within linguistic theory. Rather, I will look at a variety of mechanisms that stand the sharpest tests for innateness, and discuss which ones are good candidates for UG membership and why.

A secondary goal of mine is to bring to the attention of linguists results and findings from neighboring fields within cognitive science that bear on the issue of innateness and specificity in language. I have been trained as a theoretical linguist, and I have become increasingly engaged in cooperative, experimental research with cognitive psychologists. I believe the benefits of this interdisciplinary way of working largely surpass the frustrations and communication difficulties that are inevitably encountered along the way.

I will discuss discoveries related to innateness and specificity relatively well known by language researchers within cognitive psychology, but perhaps not very well known in the linguistics community, and discuss their relevance both to the research program that took off some fifty years ago with the birth of generative grammar, and to our current concepts of grammar and language. I  also want to caution against the temptation to take it for granted that any innate properties found in language must necessarily be part of UG. Innateness (by which word I mean experience-independent properties) is a necessary condition for a given mechanism to belong in UG, but not a sufficient one: specificity is also required.

Hence, UG should contain those properties of language, if any, that cannot be fully accounted for elsewhere, for example in the sensory-motor side of language or in the conceptual-semantic component, both of which predate grammar. This approach, this research strategy, takes the name of Minimalism (Chomsky 1995) and necessarily causes us to reflect on what UG is and to try to reduce it, trim it and pare it down to its bare necessities.

The term universal grammar is not used in the 1959 review, but the hypothesis, though nameless, was already there, right at the start. In fact, the word “innate” appears three times in the review, once referring to imprinting in animals, and twice referring to human language in the context of language acquisition. One instance is this:

As far as acquisition of language is concerned, it seems clear that reinforcement, casual observation and inquisitiveness (coupled with a strong tendency to imitate) are important factors, as is the remarkable capacity of the child to generalize, hypothesize and process information in a variety of very special and apparently highly complex ways which we cannot yet describe or begin to understand, and which may be largely innate, or may develop through some sort of learning or maturation of the nervous system. (Chomsky 1959)

We can see that Chomsky is not saying that imitation is irrelevant for the acquisition of language; he is simply making the point that it will not suffice to tell the whole story. In fact imitation is a crucial, rather distinctive property of humans, and our imitation is highly sophisticated (Meltzoff and Printz 2002). Despite this, language acquisition researchers have found abundant evidence that imitation alone does not account for language learning.

The crucial issue in the quote is that it appeals to (then unknown) conditions that determine the process of language acquisition – i.e., hypothetical acquisition mechanisms which were “complex ways which we cannot yet describe or begin to understand”. Today, although we still do not fully understand them, we have come a pretty long way. Some of the “special and apparently highly complex ways” in which infants process linguistic input have been discovered in recent years. Moreover, in considering acquisition of the lexicon, Chomsky (1959) says:

It is possible that ability to select out of the auditory input those features that are phonologically relevant may develop largely independently of reinforcement, through genetically determined maturation. To the extent that this is true, an account of the development and causation of behavior that fails to consider the structure of the organism will provide no understanding of the real processes involved.

Again, though at the time they stirred minds and thoughts, from a contemporary perspective these words do not say anything out of the ordinary; there is widespread agreement that, already at birth, infants do in fact select certain features from the auditory input. Today, few experts would disagree with the claim that it is crucial to know the structure of the human brain and its maturation in order to have a full picture of language acquisition. It is about the nature, specificity and extent of these organism-internal conditions that the debate is taking place nowadays.

In 1959, however, none of this was so clear. In discussing Lashley’s work on neurological processes, Chomsky (1959) proposed a research program for linguistics:

Although present-day linguistics cannot provide a precise account of these integrative processes, imposed patterns, and selective mechanisms, it can at least set itself the problem of characterizing these completely.

This research program should be of relevance to the study of the brain, and vice-versa:

The results of such a study [of the characterization of the mechanisms of language] might, as Lashley suggests, be of independent interest for psychology and neurology (and conversely).

These statements, which sounded extremely foreign to people in linguistics and psychology at the time, paint a landscape that has become the dwelling space of contemporary linguistics and cognitive science. This expectation of mutual importance and increasing convergence is our present: there is a vast amount of research in human language where linguists listen to what other fields can contribute about human language, and conversely. In sum, the two main conceptual seeds in the review of Verbal Behavior have clearly stood the test of time and bloomed. The first such seed is that there are innate aspects to our knowledge of language, and the second one is that if we want to understand them, we first need to know what language is like. Finding this out is the natural research program for linguistics.

To answer the question of what language is like, we turn now to Chomsky’s 1957 work, Syntactic Structures. This small book, which had a hard time finding a publisher, was very successful. It proposed an approach to the study of language that set up most of the foundational issues still in the background of the discussion today, as I would like to show you. The goal of linguistics, according to Syntactic Structures (p. 11) is to determine:

… the fundamental underlying properties of successful grammars. The ultimate outcome of these investigations should be a theory of linguistic structure in which the descriptive devices utilized in particular grammars are presented and studied abstractly, with no specific reference to particular languages.

Whereas the review of Verbal behavior is very much concerned with biological aspects of language, Syntactic Structures focuses on the formal architecture of grammar and its abstract properties, without mentioning biology or psychology. Years later, in the eighties, both sides of this research program, the biological/psychological side and the formal side, would appear hand in hand, as in this more recent quote from Knowledge of Language (Chomsky 1986: p. 3):

The nature of this faculty is the subject matter of a general theory of linguistic structure that aims to discover the framework of principles and elements common to attainable human languages; this theory is now often called “universal grammar” (UG), adapting a traditional term to a new context of inquiry. UG may be regarded as a characterization of the genetically determined language faculty.

Universal grammar should therefore be the genetically determined part of language and would include those aspects of language that are not determined by experience. However, primitives and mechanisms involved in language that are not specific to language could (and should) be excluded from UG, because they belong to broader or related but independent cognitive domains. This naturally brings us to consider innateness and specificity in greater detail. These two properties are not synonymous, for a given trait might be innate in a species, but not specific to it, as is the case with fear of snake-like forms in mammalians. Also, there are increasingly restrictive degrees of specificity, relative to a species or relative to a cognitive domain. A given property could be human-specific, but not necessarily language-specific. This point was already discussed in the Royaumont debate in 1975, as this remark by Chomsky shows:

On this point I agree with Premack. I think he is right in talking about two different problems that enter into this whole innateness controversy. The first is the question of the genetic determination of structures… the second problem concerns specificity. (Piattelli-Palmarini 1980)

There are phenomena that constitute necessary prerequisites for language, which are innate but which are clearly not specific, either to humans or to language. However, in the history of discovery, such phenomena have often been thought (especially when noticed for the first time) to be specific to language. A lesson from history, therefore, is that when in our research path we find something characteristic of human language, we would be wise to check whether it is really specific to humans and specific to language.

In following posts, I will consider some examples that looked like good candidates for UG properties that turned out not to be, and I will progress in increasing levels of apparent specificity, that turn not to be so, until we find what is left of the UG hypothesis as the repository of linguistic specificity.

Recently, Christophe Pallier and collaborators at the CNRU have published results that locate the brain sites where constitutent-structure is computed in the brain. One central claim in Linguistics is that sentences are not mere strings of words but possess a hierarchical structure with constituents nested inside each other; this is in fact one of the central arguments made by Chomsky in Syntactic Structures (1957).

phase-structure representation

The researchers used functional magnetic resonance imaging (fMRI) to search for the cerebral mechanisms of linguistic constituents. They used various types of stimuli: some consisted of mere strings of words that had no phrase-structure, others consisted of sequences of phrases arranged in increasing complexity. Out of these, some where constructed with funtional and lexical words, while others contained functional words and nonsese lexical items (jabberwocky).

Results isolated a network of left-hemispheric regions that operate autonomously of other language areas and compute  abstract syntactic frames based on function words and morphological information alone, that is, these areas compute syntactic structure specifically.

Christophe Pallier

Christophe Pallier will present this research to us tomorrow March 16th, and we will have a chance to discuss it and its implications. Before the afternoon talk, Pallier and Erdocia will present and discuss some experimetal results from an artificial language paradigm experiment run in our lab.

Here you can read the paper, entitled  Cortical representation of the constituent structure of sentences.

This is an intriguing and currently much inquired question, which can help us unravel more than one mystery concerning language and the brain. At present, we only know bits and pieces of the answer. As research progresses and more pieces of this large and complex puzzle fit together, we discover some general outlines of the answer, and realize the intricacies of the detail.  Here I will attempt to keep our eyes set in that general outline,  occasionally dwelling into a detail or two, in the hope of giving you a glimpse of how research is conducted in this field of inquiry.

There are indeed differences that relate to having more than one language in the brain. Some of these differences involve cognitive abilities that lie outside of the linguistic systems proper, such as the capacity to ignore irrelevant information when changing tasks, or a certain degree of resilience towards symptoms of neurodegeneration (such as Alzheimer’s disease, in a related post) .

Other differences between monolinguals and bilinguals involve the interplay of the two linguistic systems: their simultaneous activation and the need to select or inhibit one at a time, or the cost involved in having two lexicons and grammars instead of one.

The developmental patterns of preverbal bilingual babies are also different from those of monolinguals. Bilingual preverbal babies detect very early that there is more than one language in their environment, as recently shown by Ágnes Melinda Kovács and Jacques Mehler in a Science paper entitled “Flexible Learning of Multiple Speech structures in Bilingual Infants“.

Children acquire their native language according to a well-defined time frame. Surprisingly, although children raised in bilingual environments have to learn roughly twice as much about language as their monolingual peers, the speed of acquisition is comparable in monolinguals and bilinguals. Here we show that preverbal 12-month-old bilingual infants have become more flexible at learning speech structures than monolinguals. When given the opportunity to simultaneously learn two different regularities, bilingual infants learned both, whereas monolinguals learned only one of them. Hence, bilinguals may acquire two languages in the time in which monolinguals acquire one because they quickly become more flexible learners. (Abstract, Kovács and Mehler 2009)

These differences eventually emanate from the intensive cognitive training undergone by bilinguals in their lifetimes, given the frequency and speed at which they switch from one language to another.

From a more narrowly linguistic point of view, humans that have more than one language in their brains can provide crucial evidence regarding the neurocognitive nature of the language faculty, with its innate/universal properties and its acquired/variable aspects.

T-Rex lecturing

Thus, for instance, we will see that variable (parametric) aspects of the grammar appear to be sensitive to when they are acquired, and to what type of grammatical knowledge was there before, so that native speakers and non-native speakers do not process certain aspects of the grammar in the same way, even at high levels of language proficiency. In contrast, the lexicon seems to be insensitive to when it is acquired and what the words of a previously acquired language look like: at  high proficiency, non-native speakers are native-like in lexical matters.

So, in broad terms, it matters a great deal to the brain whether it carries more than one language, and when there is more than one, which one developed first  and which one later, and it also depends on the language component what is the length of time that matters (shorter lapse between native and the non-native language for phonology, longer lapse for syntax, insensitive for the lexicon). It also matters to the brain how present these languages are, that is, what the proficiency achieved in each language is, and how frequently the brain uses them, or changes from one to the other, so that in some cases one language can be dominant over another, or not. There are also reasons to think that individuals vary in their abilities to acquire a second language, and that this abilities relate to intrinsic neurobiological differences differences (Díaz et al. 2008). The degree of morphosyntactic similarity of the languages coexisting in one brain might also make a significant difference in how we represent and process them, though currently, more is known about the lexicon and phonology in humans that know more than one language, than about the syntax. Perhaps this is partly due to the fact that the finer experimental studies exploring syntax in the brain often require the cooperative work of syntacticians, psycholinguists and neuroscientists, which hopefully books like this will encourage.

The literature covering various aspects of the topic  is vast, and it is therefore not possible to cover it exhaustively. In these posts, I will provide an overview of the main topics of research and the general outlook that emerges given the evidence found; and since it is not possible to discuss all issues on an equal footing, I will mainly concentrate on those that I find most significative and revealing for linguists with an interest in the neurobiology of language.  I will comment on recent findings on cognitive advantages of bilingualism that are not directly related to the language faculty, and discuss the impact of age and language proficiency in the neural underpinnings of bilingualism. Within the components of language, I will concentrate more on the lexicon and the grammar.

Bilingual phonology is a fascinating area of research that directly touches upon earliest stages of language acquisition, but I will not discuss it here. There are excellent overviews of bilingual language acquisition that focus on the early development of phonology and the lexicon, which address the issues that I will leave aside, such as Sebastian-Galles and Bosch (2002), Sebastian-Galles et al. (2005), and Sebastian-Galles and Kroll (2003).

REFERENCES:

Diaz, B., Baus, C., Escera, C., Costa, A., and Sebastian-Galles, N. (2008). Brain potentials to native phoneme discrimination reveal the origin of individual differences in learning the sounds of a second language. Proceedings of the National Academy of Sciences, 105(42), 16083-16088.

Kovács A.M. and J. Mehler (2009) Flexible Learning of Multiple Speech Structure in BilingualInfants. Science Vol. 325 no. 5940 pp. 611-612

Sebastian-Galles, N., & Bosch, L. (2002). The building of phonotactic knowledge in bilinguals: The role of early exposure. Journal of Experimental Psychology: Human, Perception and Performance, 28, 974–989.

Sebastian-Galles, N., Echeverrıa, S., & Bosch, L. (2005). The influence of initial exposure on lexical representation: Comparing early and simultaneous bilinguals. Journal of Memory and Language, 52, 240–255.

Sebastian-Galles, N., & Kroll, J. F. K. (2003). Phonology in bilingual language processing: Acquisition, perception and production. In N. O. Schiller & A. S. Meyer (Eds.), Phonetics and phonology in language comprehension and production (pp. 279–317). Berlin: Mouton de Gruyter.

Sebastian-Galles, N., & Soto-Faraco, S. (1999). On-line processing of native and non-native phonemic contrasts in early bilinguals. Cognition, 72, 112–123.

As we discussed in class, during the last years the field of early language acquisition has progressed enormously, and many discoveries have been made. Here I post to review papers (of the many that could be read) that summarize what is known regarding what it is babies do to grapple with language from the onset of their lives.

The first paper, by Rebecca Gómez and   LouAnn Gerken, is a review of the tipe of segmentation strategies babies use, and contains a discussion of statistical learning, which was shown by Jenny Saffran and collaborators to be a mechanisms that babies emply to segment the speech stream. Statistical learning is thus an example of a perceptual mechanism that is not specific to language but is necessary to acquire it.

Gomez and Gerken 2000 TICS

The second paper, by Jacques Mehler, Nuria Sebastián-Gallés and Marina Nespor, is also a review of early acquisition that distinguishes mechanisms that segment the speech signal in terms of adjacent probabilities (looks at a flat sequence and cuts chunks in it), from mechanisms that infer relations among non adjacent elements. While the first is not language specific, the second one is argued by the authors to be specific to language:

Mehler, J., N. Sebastian Galles e M. Nespor (2004) Biological foundations of language: language acquisition, cues for parameter setting and the bilingual infant. In M. Gazzaniga (ed.) The New Cognitive Neurosciences III. Cambridge, MA. MIT Press, pp.825-836.

find it here, in the section “books and chapters”

Grosjean

François Grosjean, a pioneer researcher on bilingualism, warned all neurolinguists in his 1989 paper that the bilingual is not two monolinguals in one person. In this chapter, we will review some discoveries on the neurobiology of bilingualism that show the extent to which this statement is true. We will also keep our focus on what these discoveries reveal about the human language faculty, and the new questions they pose to language research.

Bilinguals outnumber monolinguals in our species: according to some recent estimates, between 60 and 75 per cent of the world’s population is bilingual. Although we do not have direct evidence, it has been argued that the capacity to learn more than one language is an adaptive trait in human evolution (Hirschfeld 2008); given what we know of interactions between human groups, is not unlikely that people throughout history have more often than not known more than one language.

For opur pruposes, a person who knows more than one language and can use them to communicate efficiently qualifies as bilingual, even without reaching native-like command in both languages. We will thus adopt the view that “bilingualism is the regular use of two (or more) languages, and bilinguals are those people who need and use two (or more) languages in their everyday lives” (Grosjean 1992). We will not limit our attention to people who can speak two languages with equal mastery, often referred to as “balanced bilinguals”; we will also review studies of “unbalanced bilinguals”, for whom one language is dominant over the other in some or another aspect. Finally, we will also consider  adults in the process of learning a second o third language from the start. All these people are of interest to the neurobiology of language; we can learn a great deal about language in the brain by considering all kinds of different types of populations.

Psycholinguistic and neurolinguistic research initially tended to restrict itself to the study of monolinguals, and there was not much interest in the study of  bilingualism, because it was generally (though tacitly) thought that the neural representation and processing of a given language was not affected by another language, whether acquired simultaneously or later in life. Recent findings challenge this assumption, and suggests instead that research beyond monolingualism holds a great potential for generating knowledge about the neurobiological nature of the human language faculty and the way in which language is organized in our brains.

Broadly speaking, neurocognitive studies of language and bilingualism reveal that the patterns of activation related to language processing are consistent across languages and native speakers; research shows that the processing of different languages occurs in much of the same brain tissue (Kim et al. 1997; Perani et al. 1998; Díaz et al. 2011).

early bilingual (from Kim et al. 1997)

late bilingual (from Kim et al. 1997)

When differences between languages are found, they obtain in bilinguals and they correlate with differences in proficiency levels attained in each language, and differences in age of acquisition for each language. This is why the impact of language proficiency and of the age at which a language is acquired have been to date the factors that have received most research attention.

The impact of the degree of similarity of the grammars located in one brain is a far less explored issue, as are the differences among different types of grammatical phenomena, though as our knowledge advances, grammatical specificity emerges as a likely relevant factor to be kept into account. As the volume and level of detail of the studies carried out increases, it also becomes increasingly clear that, although all these factors have often been studied separately, there are strong connections between them: proficiency in the language, age of acquisition, and grammatical similarity are likely to be intertwined rather than separate factors.

REFERENCES:

Díaz, B., Sebastián-Gallés N., Erdocia, K., Mueller J., Laka I. (2011) On the cross-linguistic validity of electrophysiological correlates of morphosyntactic processing: A study of case and agreement violations in Basque. Journal of Neurolinguistics 24, 357–373

Grosjean, F., (1989) Neurolinguists, beware! The bilingual is not two monolinguals in one person. Brain and Language 36 (1), 3–15.

Grosjean, F. (1982). Life with Two Languages: An Introduction to Bilingualism. Cambridge, Mass: Harvard University Press.

Hirschfeld A. L. (2008) The Bilingual Brain Revisited: A Comment on Hagen (2008) Evolutionary Psychology. Volume 6(1): 182-185

Kim, K. H., Relkin, N. R., Lee, K. M., & Hirsch, J. (1997). Distinct cortical areas associated with native and second languages. Nature, 388(6638), 171–174

Perani, D., Paulesu, E., Sebastian-Galles, N., Dupoux, E., Dehaene, S., Bettinardi, V., Cappa, S. F., Fazio, F. and Mehler, J. (1998) The bilingual brain: Proficiency and age of acquisition of the second language. Brain, 121,1841-1852.

Babies’ language skills are amazing.  Infants can distinguish between two languages they’ve never heard before just by looking at the face of a speaker. And this ability is enhanced if they’re raised in a bilingual household.

An Infant’s Refined Tongue – ScienceNOW.

Here is the paper, with all the details:

visualdiscrimination07

Perhaps the most strinking findings from neurocognitive research on bilingualism relate to cognitive differences related to using more than one language frequently during a lifetime.

There are indeed differences that relate to having more than one language in the brain. Some of these differences involve cognitive abilities that lie outside of the linguistic systems proper, such as the capacity to ignore irrelevant information when changing tasks, or a certain degree of resilience towards symptoms of neurodegeneration.

Other differences between monolinguals and bilinguals involve the interplay of the two linguistic systems: their simultaneous activation and the need to select or inhibit one at a time, or the cost involved in having two lexicons and grammars instead of one. The developmental patterns of preverbal bilingual babies ―who detect very early that there is more than one language in their environment― is also different from that of mo nolinguals. These differences eventually emanate from the intensive cognitive training undergone by bilinguals in their lifetimes, given the frequency and speed at which they switch from one language to another.

The cognitive capacities that are enhanced by bilingualism are not language-specific, though it is through the acquisition and use of more than one language that they have been trained and strengthened. Bilinguals extract cognitive benefits in the areas of the brain that constitute  the executive control system. Recent research has shown that bilinguals use Broca’s area for linguistic and non-linguistic task-switch, whereas monolinguals rely more on righ-hemispheric areas. Very possibly,  neuroanatomical differences caused by a lifetime of bilingualims are the key factor that makes bilinguals resist longer without symptoms of neurodegeneration (a mean of 4-5 years of delay in the appearance of symptoms of alzheimer, for instance).

If you want to read more…

Being bilingual may delay Alzheimer’s and boost brain power | Science | The Guardian.

Video: the importance of being bilingual

Without language, numbers make no sense – health – 07 February 2011 – New Scientist.

Deaf Nigaraguans chatting

Nicaraguan Sign Language in Wikipedia

You can also read about the Munduruku people here:

Munduruku People in Wikipedia

As Idoia Ros suggests, you can all see what numeral systems there are across languages by cheking into WALS, a rather thorough linguistic atlas online:

Numeral bases across languages

And here you can find the paper on the development of numerical systems in the Amazonian languages that Dorota suggested:

Numbers in the Amazons

Patience Epps, University of texas at Austin:

” Numerals in many languages around the world can be argued to reflect a progressive build-up of historical stages (cf. Hurford 1987), each of which may also represent the synchronic upper limit of a numeral system in another language. This paper presents an intriguing test case of this claim by exploring the historical development of numerals in the languages of the Nadahup (Makú) family of the northwest Amazonian Vaupés region, in which the numeral strategies that can be inferred diachronically for one language are also represented synchronically in its sisters. The paper also demonstrates that even the most basic of the Nadahup numerals have transparent etymologies (a cross-linguistically unusual feature suggestive of their relatively recent development), and that areal diffusion contributed to the expansion of the systems, supporting the characterization of the Vaupés as a linguistic area.”

Patience Epps (2006) Growing a numeral system. The historical development of numerals in an Amazonian language family Diachronica 23:2 (2006), p. 259-288

What determines the length of words? MIT researchers say they know: A word’s length reflects the amount of information it contains.

Wordly wisdom.