language

Chris at Mixing Memory has a post from last week reflecting on the meaning of the finding that starlings can learn certain patterns of syntactic recursion.

He also links to two message-board posts by linguists on the topic. This one, by Mark Liberman explains why recursion is important and what a Dyck language is:

If you're like every other human I've tested, you find this task pretty hard. If you're quick and you care enough, you can count on your mental fingers, so to speak, adding one for each higher pitch and subtracting one for each lower pitch, and "parse" the sequence that way. But the difference between the Dyck and non-Dyck patterns is not, in the general case, cognitively salient to humans without intellectual scrutiny. In contrast, we don't need to count on our mental fingers to understand the structures of real spoken language. And I'd be astounded if the difference between Dyck and non-Dyck strings is cognitively salient to starlings or to any other animals either.

This post by David Beaver has a practical illustration, and reflects on the study:

Faced with the facts about starlings innate ability to learn Dyck languages, and the facts about center embeddings for you and me, a contrarian might well conclude that yes, at last, we have firm and amazing evidence for a biologically unique language module. The trouble is, starlings have it, and we don't.

And this post at Tenser, said the Tensor is another explanation:

However, this does not imply that the birds are recognizing context-free languages when they're processing the songs. It's true that CFGs are the next step up the Chomsky hierarchy from regular languages, but that's a fact about the hierarchy, not about the universe -- there are other kinds of languages that are supersets of the regular languages while still being subsets of context-free languages. The researchers propose a few of these and show why they're not sufficient to account for the birds' success, but I suspect the birds may be processing one they didn't consider. In particular, the starlings may just be using memory.

It's heavy stuff, but important to the evolution of language, since it reflects on the logical prerequisites for generating and processing linguistic messages.

Meanwhile, before I posted, I found that Carl Zimmer has written about the study for the NY Times. Nice exchange between Gentner, Chomsky and Hauser at the end:

Dr. Chomsky also rejects Dr. Gentner's conclusions. He suggests the starlings are merely counting rattles, storing the number in their memory, then counting warbles. "It has nothing remotely to do with language -- probably just with short-term memory," he said via e-mail. Dr. Gentner argues that even if the starlings are counting, they are still using a strategy more sophisticated than has been seen before in animals.

"Chomsky may find this trivial, but that is a bit like saying apes use tools, but only the trivial kind that lack the sophistication of a tri-square or a laser level," he said.

Carl Zimmer has an article in Forbes covering recent experiments in chimpanzee vocal communication.

But don't write off those grunts and hoots just yet, at least according to a new study that appears in the Oct. 15 issue of the journal Current Biology. Katie Slocombe and Kaus Zuberbuhler, two primatologists at the University of St. Andrews in Scotland, investigated a particular noise chimpanzees make when they find food, called a "rough grunt." At the Edinburgh Zoo, the scientists fed the chimpanzees two different foods--apples and bread--and recorded the sounds they made. Chimpanzees prefer bread to apples, and Slocombe and Zuberbuhler discovered a corresponding difference in the rough grunts they made for each food. They hit a distinctively high note when they came across the bread, and but made lower and noisier grunts for apples.

It's a short article, supplemented by an entry on the Loom.

This online issue of Forbes

There are a number of short interview excerpts in the issue. One has Noam Chomsky discussing spontaneous language innovation in deaf communities. Another from Jane Goodall on the perils of e-mail communication:

I remember when I worked for Lewis [sic] Leakey, first as his secretary. He was very impulsive. He'd get a letter in the mail, and he would open it, and it would be perhaps something from a scientist he thought was quite ridiculous. You could hear him muttering "Bosh! Rubbish!" The poor bit of paper would be scored with his marks, and he'd turn to me and say "Get so and so on the phone!" I got very wise to his moods, so I would pretend the number was engaged, or the man wasn't there, and then an hour or two later, he was rational again.

And other interviews and articles, with Arthur C. Clarke, Wil Wheaton, Desmond Morris, Steven Pinker and many others. Many thanks to the reader who pointed me to the site.

This week's (9/27/95) PNAS has an article by Johannes Ziegler and colleagues (Université de Provence) titled, "Deficits in speech perception predict language learning impairment". The paper concerns specific language impairment, or SLI.

Readers may remember that a rare monogenic form of SLI is the disorder that led to the identification of the FOXP2 gene (OMIM). Later work showed that most SLI is not directly caused by FOXP2 variants, but apparently the adjacent cystic fibrosis gene (CFTR) does show a strong association with SLI. Interesting.

The current study investigated the behavioral correlates of SLI to see what might cause the language learning deficits. The abstract:

Specific language impairment (SLI) is one of the most common childhood disorders, affecting 7% of children. These children experience difficulties in understanding and producing spoken language despite normal intelligence, normal hearing, and normal opportunities to learn language. The causes of SLI are still hotly debated, ranging from nonlinguistic deficits in auditory perception to high-level deficits in grammar. Here, we show that children with SLI have poorer-than-normal consonant identification when measured in ecologically valid conditions of stationary or fluctuating masking noise. The deficits persisted even in comparison with a younger group of normally developing children who were matched for language skills. This finding points to a fundamental deficit. Information transmission of all phonetic features (voicing, place, and manner) was impaired, although the deficits were strongest for voicing (e.g., difference between/b/and/p/). Children with SLI experienced perfectly normal "release from masking" (better identification in fluctuating than in stationary noise), which indicates a central deficit in feature extraction rather than deficits in low-level, temporal, and spectral auditory capacities. We further showed that speech identification in noise predicted language impairment to a great extent within the group of children with SLI and across all participants. Previous research might have underestimated this important link, possibly because speech perception has typically been investigated in optimal listening conditions using non-speech material. The present study suggests that children with SLI learn language deviantly because they inefficiently extract and manipulate speech features, in particular, voicing. This result offers new directions for the fast diagnosis and remediation of SLI.

From an evolutionary perspective, a disorder that affects 7 percent of people is not a disorder; it is a normal variant. The 7 percent value comes from a study by Tomblin et al. (1997), who screened a sample of over 7000 monolingual English speaking kindergarteners, finding only small differences between boys and girls in the incidence of SLI. Such a high frequency raises a question: Why has this apparent problem persisted in human populations, when it would seem that language ability is very important to survival and successful integration into society?

Of course, more basic statistical answers must come before we worry too much about the evolutionary history of SLI. For one thing, is this actually a unique phenotypic variant, or is it merely the end of a continuous distribution of language-learning skill in children? And are all cases of SLI actually part of a single package of correlated symptoms, or is there a broader spectrum of different deficits in language learning that belong to the disorder?

The current paper by Ziegler et al. (2005) starts by looking at the actual behavioral correlates of SLI. The introduction to the paper gives some background on the issues:

The causes of SLI are still hotly debated. Current theories of SLI fall into two categories: those that attribute SLI to a specifically linguistic deficit and those that attribute SLI to general processing limitations (for a review, see ref. 5). Linguistic deficit theories typically assume that children with SLI have difficulty acquiring linguistic mechanisms, such as past tense rules or the grammatical principle of inflection (6, 7). Children with SLI are thought to be "stuck" at an early stage of grammatical development. Such a delay could actually reflect a general maturational delay of language and other cognitive systems (8, 9).

In contrast, general processing deficit theories assume that it is not the specific nature of the material that is important but rather how it is processed in the brain. Nonlinguistic deficits in either perception or memory are thought to be responsible for language disorder (10Ð12). The most prominent theory of this kind, also called the fast temporal-processing deficit hypothesis, maintains that SLI is a consequence of a deficit in processing brief and/or rapidly changing auditory information and/or in remembering the temporal order of auditory information (13Ð16). For example, Tallal and Piercy (13) found that some children with SLI have difficulty reporting the order of pairs of high- and low-frequency sounds when these sounds are brief in duration and presented rapidly. Such a deficit may underlie difficulties in perceiving grammatical forms (e.g., the or is), which are generally brief and unstressed (17).

The paper additionally presents possible criticisms of these views. The main idea of the research presented here is to test the hypothesis of auditory processing deficits by looking not at kids in sterile laboratory settings, but in normal listening conditions with background noise. The logic is that they might have trouble distinguishing speech sounds within complex aural environments.

The discussion fairly succinctly states the results:

The main findings of the present study can be summarized as follows. Under optimal listening conditions (silence), children with SLI showed only subtle speech perception deficits. However, under conditions of stationary noise and fluctuating noise, children with SLI showed substantial speech perception deficits. Note that conditions of fluctuating noise are not artificial; they are actually very representative of the kind of listening conditions that children will encounter in their daily life (in schools, for example). Thus, the present results raise the possibility that children with language learning disabilities have very serious problems with noise exclusion, which will certainly have tremendous consequences for normal phonological development. A similar proposal has recently been made with regard to visual (magnocellular) deficits that seem frequently associated with dyslexia (45). The authors showed that dyslexic children do not have visual (magnocellular) processing problems per se but rather problems of noise exclusion that become apparent in visual tasks using noisy displays. Noise exclusion could therefore be a very general problem responsible for poor phonological development of children with language learning problems and dyslexia.

To me, this is illuminating about the frequency of the disorder. If the problem is distinguishing sounds quickly and accurately in a complex aural environment, then it may be a problem that manifested much less, or possibly not at all, before people began living in crowds. The comparison with dyslexia may be quite relevant, since, of course, people didn't have to read through most of human existence either. This does leave the question of why the variation exists as it presently does. Are there other behaviors that weigh in a different direction from language learning? Is ADHD a pertinent analogy? Are there alternate strategies for learning langauge?

Probably the most important thing would be to get a better idea of the cross-cultural incidence of these traits. If SLI is really significantly associated with CFTR, there might well be significant variation among populations today. Just a glimpse into what child psychology can tell us about the evolution of culture.

References:

Tomblin JB, Records NL, Buckwalter P, Zhang X, Smith E, O'Brien M. 1997. Prevalance of specific language impairment in kindergarten children. J Speech Lang Hear Res 40:1245-1260. PubMed

Ziegler JC, Pech-Georgel C, George F, Alario F-X, Lorenzi C. 2005. Deficits in speech perception predict language learning impairment. Proc Nat Acad Sci USA 102:14110-14115. Full text online

Carl Zimmer has put together this week's news about language evolution. In one paper, mice with knockout versions of the FoxP2 gene were found to have trouble with their squeaks! In other words, the gene may be involved in vocal communication in most mammals. The second paper demonstrates the existence of a neural area homologous with Broca's area in macaques. This would show that one cortical region underlying language function in humans is broadly shared among anthropoid primates, although not elaborated to the extent found in living and fossil Homo.

Both of these are stories about homology. Humans aren't unique in the presence of either FoxP2 or Broca's area. Instead, these emerged long ago. Both of them may have been involved in vocal communication for a long time in our lineage, in other primates, and potentially in many other mammals.

So human evolution didn't have to originate new language-related functions for these elements out of whole cloth. There was already a simple structure there to work with. Human evolution elaborated on this ancient foundation.

The details, of course, remain to be worked out. FoxP2 is far from the only gene related to language, and Broca's area is far from the only cortical region. Different areas may have yet other origins, may have been put together in new ways during human evolution, and may have been expanded upon (or in some cases possibly even reduced) to result in our unique configuration.

Anyway, read Zimmer, and I may write more on the Broca's discovery later.