Tag: evolution

Specific Language Impairment, Autism and Language Evolution

My last post speculated about what some conditions which manifest impaired theory of mind could tell us about the evolution of ToM. Of these conditions autism was one which could be the most informative when it comes to looking at the genetics of how ToM evolved, in this post I will look at what autism could tell us, not only about theory of mind, but also about other aspects of the language faculty.

Dorothy Bishop has recently written a paper exploring the above average co-occurrence of Specific Language Impariment (SLI) and Autistic Spectrum Disorders (ASD).

SLI is a condition where a child fails to develop spoken language on the normal schedule, for no observable or obvious reason (Bishop and Norbury 2008). Whilst ASD and SLI are regarded as distinct conditions, these disorders co-occur at above chance levels.

Bishop (2010) explores why this might be. Bishop begins her paper by painting a textbook example of a child with SLI. This example is of a child with normal social interaction and nonverbal communication, but with specific difficulties in mastering structural aspects of language, especially syntax and phonological skills. So this typical picture is not one of an autistic child in that one of the defining features of autism is a limited capacity for normal social interaction and a child is much more likely to be deficient in pragmatic skills than syntactic or phonological skills.

Bishop states that despite the fact that according to conventional diagnostic frameworks, SLI andASD are mutually exclusive diagnoses, similarities exist between the two conditions and these include:

  • They are both highly heritable
  • Identical, monozygotic twins are significantly more concordant than fraternal, dizygotic twins for autism and SLI
  • In both conditions rates of impairment in first degree relatives are higher than in the general population
  • First degree relatives of affected individuals of both conditions often manifest sub-threshold symptoms
  • These conditions correspond to points on a continuum of impairment, rather than all-or-none diseases

So any model of causation for either condition must take into account the following considerations:

  • Above chance levels of comorbidity between SLI and ASD
  • Rates of language impairment in relatives of probands with SLI and ASD
  • Molecular genetic findings of shared genetic risk factors for ASD and SLI

Now the article goes on to explore etiological models which explain these considerations with varying degrees of success. I’m not going to pretend to understand these models as I have only ever been formally taught in linguistics and so I’m a bit stumped by genetic psychology. If you’re much smarter than me you can read the article yourself here:

http://www.springerlink.com/content/gg087q4h51j5127g/fulltext.pdf

So what I got from this article was that the genetic factors involved in autism can not only cause the characteristics typical of a person with autism (pragmatic impairments) but also other language impairments which are typical of a person with a Specific Language Impairment. Specifically the CNTNAP2 gene has been found in independent samples to be associated with both ASD and SLI. This is interesting because it could show that gene mutations which cause improved social abilities could have also caused changes in our linguistic ability on a syntactic or phonological level.

Disclaimer: Sorry if I’ve made too many assumptions in the conclusion I’ve just drawn. As I said above I know next to nothing about genetic psychology but I just felt this research would have interesting consequences in the field of language evolution. I’d love to hear the thoughts of people who know better than I do.

References

Bishop, DVM. (2010) Overlaps Between Autism and Language Impairment:
Phenomimicry or Shared Etiology? Behavior Genetics 40:5, 618-629

Bishop DVM, Norbury CF (2008) Speech and language disorders. In: Rutter M, Bishop DVM, Pine D, Scott S, Stevenson J, Taylor E, Thapar A (eds) Rutter’s child

Theory of Mind and Language Evolution; What can psychopathology tell us?

Theory of Mind is the ability to infer other persons’ mental states and emotions. It is thought to have evolved as part of the human’s social brain and probably emerged as an adaptive response to increasingly complex primate social interaction.

Brüne and Brüne-Cohrs (2006) explore the ‘evolutionary cost’ of language evolution:

This sophisticated ‘metacognitive’ ability comes at an evolutionary cost, reflected in a broad spectrum of psychopathological conditions. Extensive research into autistic spectrum disorders has revealed that theory of mind may be selectively impaired, leaving other cognitive faculties intact. Recent studies have shown that observed deficits in theory of mind task performance are part of a broad range of symptoms in schizophrenia, bipolar affective disorder, some forms of dementia, ‘psychopathy’ and in other psychiatric disorders.

Now it’s fairly uncontroversial to assert that without the ability of theory of mind humans would have never evolved language (Sperber and Wilson, 2002). This is due to the fact that if one can’t attribute another to have a ‘mind’ like ones own, or assume that other minds hold different information to ones own then one would see little point in trying to share information. (I’m sorry for the amount of ‘ones’ in that sentence).

Sooo, it does not seem presumptuous to assume that people interested in the evolution of language should be interested in theory of mind, in fact for many years evolutionary linguists, psychologists and biologists have been looking into this, but mostly through observing the behaviour of animals, and especially primates to see if they display theory of mind capabilities. A good summary of this work can be found here, and a lot of relevant studies can be found on this blog in the What makes humans unique? posts by Michael. I’m not going to look at the animal data in this post, but instead what the deficiencies in some human conditions can tell us about the evolution of theory of mind. That is, what can autism, schizophrenia, bipolar affective disorder, dementia, ‘psychopathy’ and other psychiatric disorders tell us?

Continue reading “Theory of Mind and Language Evolution; What can psychopathology tell us?”

Evolution of Colour Terms: 5 Cultural Constraints

Continuing my series on the Evolution of Colour terms, this post reviews studies of cultural constraints on colour naming. For the full dissertation and for references, go here.

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Some Links #15: Empires of the Word & anti-Babel

Empires of the Word & anti-Babel. It’s a few days old now but I’ve only just had time to read it. Anyway, check out Razib’s review of Empires of the Word: A Language History of the world. Lots of information for budding historical linguists and those intrigued by language spread and extinction. Particularly relevant is the following paragraph:

As I indicated above Empires of the Word is rather thin on robust generalizations. But one point which the author mentions repeatedly is that the rise and fall of languages of great expanse and utility is the norm, not the exception. In particular, Nicholas Ostler takes time out to emphasize that languages which spread via trade often do not have long term staying power. Portuguese, Aramaic, Punic and Sogdian would fall into this category (the later success of Portuguese was a matter of rice and empire in Brazil). It seems that mercantile communities are too ephemeral, that successive historical shocks inevitably result in their decline when there isn’t a peasant demographic reservoir or imperial power which imposes it by fiat. Even those languages which eventually spread beyond traders and gain cultural and political cachet may fall from grace. Greek is the best case of this. It was the dominant language of the Roman East, and spoken as far as modern Pakistan, and studied in Dark Age Ireland. By the early modern period it was a strange and foreign language in the West, and with the rise of Islam in the east it lost its cultural glamor, and even those Christians in Arab lands who were Melkite, Greek Orthodox who adhered to the theological position of Constantinople, became Arab in speech and identity (in greater Syria the Greek Orthodox have been instrumental in the formulation of Arab nationalism).

Opening a bibliography database for human evolution. Again, it’s been a few days since this was posted, but I’d advise anyone interested in human evolution visit John Hawks recently announced database. The bibliography section also has an RSS feed which provides a chronological list (newest first).

In which I apply for a job as a homeopath… Dave over at Anomalous Disaster has a great little post on him applying for a position at NHS Tayside for a homeopathic specialist. This is from the very same health board who recently brought us the sacking of 500 staff. So Dave decided to apply, which, at a cushy £68,000 salary, is definitely a job worth pursuing — after all, it can’t be that hard to dispense magic beans and provide a pseudo-scientific air of authority. Here is part of his letter of application:

The original research that I have published means that I am familiar with the body of published work on homeopathy, and the many meta-analyses and systematic reviews conducted on it. The fact that these conclude that homeopathy is no more effective than a similarly administered placebo will not bother me whilst I am taking advantage of some of the excellent salmon fishing to be found in the Tayside region. Indeed, given the fact the position only calls for the successful applicant to attend two sessions per week, I should imagine I would have plenty of time to indulge in a bit of fishing.

Click here to apply.

Selfish Sounds: Darwinism in linguistics. A brief(ish) article on the work of historical linguist, Nikolaus Ritt, and how words and sounds compete for the purpose of being replicated. Specifically, it looks at how the sound shapes of English words have gradually evolved:

Good examples of such phenomena are sets of changes which are obviously directed but unfold over time spans that are impossible to even survey by individual speakers. They have come to be known as ‘drifts’. A case of such a drift seems to have affected the sound shapes of English words (or better: lexical morphemes, i.e. the smallest linguistic units that carry meaning). Over time their shapes seem to have gradually evolved in a direction where they came to fit better into the rhythmical patterning that characterises English speech. “For instance, vowels in long words tended to be shortened over time, while vowels in short words tended to be lengthened. Thus, the rhythmic units they established became more uniform”, Nikolaus Ritt explains.

[…] From the evolutionary perspective this kind of development is best understood if one regards rhythm as an environmental constant in the linguistic world in which words and the sounds they are made up of have to survive and replicate. Because of the constant environmental pressure which rhythm exerts on them, the sound shapes of English words have gradually changed to become better adapted to the rhythmically structured utterances through which they get expressed and transmitted.

New Blog: Culture Evolves!

… Well, new to me at least. It’s run by Fiona Jordan of the Max Planck Institute for Psycholinguistics, and her latest post is an interview with one of my favourite researchers, Simon Greenhill (I didn’t know he designed a sudoku solving program). Also, after having done a little digging into her publications, I found the following forthcoming paper: The effect of population size and density on rates of linguistic evolution. Here is the abstract:

Evolutionary theory from population genetics predicts that demography may play an important role in determining the rate at which cultural and linguistic traits change over time. However, relatively few studies have explored this relationship for language at an appropriate scale and in a quantitative way, nor controlled for the problem of non-independence induced by the historical relationships between languages. Here we use phylogenetic trees of 351 Austronesian languages to test whether the rate of change in core vocabulary is affected by population size and population density. We detected a strong phylogenetic signal in both population size and density, indicating the need for historical control. We find a significant inverse relationship between lexical replacement and population size, no relationship with population density, and we confirm that splitting events influence lexical evolution. These results support the idea that a process analogous to genetic drift may be an important factor in lexical evolution. Furthermore, the strong phylogenetic signal in these demographic factors suggests that despite repeated population splits the social conditions that influence speech community size and density are maintained and inherited from one generation to the next.

I’m not going to say anything on a paper I haven’t yet read, other than it looks pretty cool and that more people should be considering the influence of demographic factors in linguistics.

Evolution of Colour Terms: 2 Environmental Constraints

Continuing my series on the Evolution of Colour terms, this post reviews evidence for environmental constraints on colour perception. For the full dissertation and for references, go here.

Continue reading “Evolution of Colour Terms: 2 Environmental Constraints”

Metroculturalism

Searching Research Blogging for “bilingualism”, two blogs dominate the recent posts: mine and Language on the Move – a blog started by Ingrid Piller and Kimie Takahashi at Macquarie University, Sydney, Australia.  Since starting last year, they have been joined by a host of international collaborators.  It’s a really well organised blog – they even have separate facebook and twitter officers!

The blog discusses topics on language learning, multilingualism and multicultural sociolinguistics.  The writers are bilingual and certainly pro-bilingualism, but it’s good to see a genuine debate over the so-called ‘bilingual edge’ (see Piller 2010- a review of ‘the bilingual edge’ which argues that differences elicited in controlled conditions don’t necessarily translate to the real world where variables are correlated).

There’s been a recent spurt of posts and publications aimed at trying to get people out of a mono-mindset.  Alastair Pennycook writes about Metrolingualism (see also, Otsuji & Pennycook, 2010) – the common use of many languages to construct identity.  He reminds us that people are most cultural traits are not mutually exclusive.  Indeed, the majority of people can communicate in many mediums.  Despite this, there is a tendency both in research and general opinion to see monolingualism as the norm and bilingualism as exceptional.

As I have mentioned elsewhere, the monolingual mindset extends into computational modelling of language acquisition and evolution.  Often, there are implicit monolingual assumptions.  On the other hand, whole paradigms such as Steels & Belpeame’s ‘Naming Game’ focus on how populations of agents can arrive at the same, single mapping between words and meanings.

In fact, there is much evidence to suggest that children can acquire multiple languages easily.  My own research focusses on a simple question – why did we evolve to be able to learn multiple languages?  It would be more efficient to have a single human language – especially if it were innately specified.  Instead, we have a culturally transmitted system that exhibits a large amount of variation.

I’m looking at two possible answers:  Either there is no selective pressure on language and bilingualism is the product of historical accident (drift) or there is an inherent advantage to the flexibility that bilingualism affords, both for communication and for the evolvability of the system.  Along the way, I’m hoping to look at whether monolingualism is a legitimate abstraction, or whether bilingualism is a fundamental part of language (for a recent talk, see here).

However, Pennycook points out the paradox of a monolingual mindset in a pervasively bilingual world, suggesting that it may be a  political affliction rather than a scientific approach:
“If we take the current sociolinguistic literature on styles, registers, discourses, genres and practices seriously, then monolingualism is also a myth: a monolingual mindset does not emerge from a state of monolingualism, because no such state can exist. If languages are myths, so too is monolingualism!”

Piller, I. (2010). The bilingual edge: why, when, and how to teach your child a second language International Journal of Bilingual Education and Bilingualism, 13 (1), 115-118 DOI: 10.1080/13670050802645942

Otsuji, E., & Pennycook, A. (2010). Metrolingualism: fixity, fluidity and language in flux International Journal of Multilingualism, 7 (3), 240-254 DOI: 10.1080/14790710903414331

Experiments in communication pt 2: Human Iterated Learning

ResearchBlogging.orgIn the last post, I discussed some of the literature into experimental communication, with the intention of then following it up by looking at recent experiments done at Edinburgh (and beyond). But as Hannah pipped me to the post, with a great overview of the wide range of experiments into language evolution, I’ll instead limit this to two relatively recent papers on Human Iterated Learning (Kirby et al., 2008; Cornish et al., 2009)

Drawing from experimental approaches found in Diffusion Chain and Artificial Language Learning studies, Kirby et al (2008) show that as a consequence of intergenerational transmission languages “culturally evolve in such a way as to maximize their own transmissibility: over time, the languages in our experiments become easier to learn and increasingly structured.” In these experiments a subject is exposed to an alien language, made up of two elements within a finite space: meanings (consisting of a picture with three discernible elements: colour, shape and movement) paired with signals (consisting of a string of letters). Importantly, the subject is only exposed to a set amount of meanings (SEEN items), after which they are then presented with a group of meanings (some SEEN, some UNSEEN) without the corresponding signal — the goal being that they provide a response (be it the correct version or not). On completion of forming the meaning-signal pairs the experiment is repeated, except this time the new subjects are trained on the data provided by the previous generation. This continues until the experiment is finished, which in this case happened at generation ten.

Continue reading “Experiments in communication pt 2: Human Iterated Learning”

Language Evolution and Tetris! Part 2

Ok, so my previous experiment was an incredible failure.  The program crashed in sixteen different ways, including suddenly deciding not to respond to key presses for no apparent reason.  A rather lazy Ghost in The Shell.  Although about 8 people participated, the data was unusable.  What on earth was I trying to achieve?

The experiment was a typical human Iterated Learning experiment (e.g. Kirby, Cornish, Smith, 2008) – there were a set of meanings (Tetris blocks) which varied along two dimensions (shape and colour).  Participants were shown the words for half of the meanings, but then asked to recall words for each meanings.  These responses were then given to the next participant as input.  Over time, other such experiments result in meanings which are compositional and more learnable.  However, the meaning space tends to ‘collapse’ as the same label is applied to many meanings.

I was trying to do an iterated learning experiment which teased apart the difference between labelling a form and labelling a function.  If participants label the function of an object, the environment will play a greater role in the evolution of the language.

There were two chains –  one played Tetris where you have to complete lines to score points – colours are irrelevant.  The other chain played “Coltris” where you scored points by placing more than 4 blocks of the same colour next to each other.  Also, each individual block in a brick finds its own lowest point (i.e. the brick breaks apart), meaning that shape is much less important. That is, for Tetris, the functionally salient feature was shape while for Coltris it was colour.

What I was hoping was that, for the Tetris players, the signal space would ‘collapse’ in the colour dimension.  That is, labels would distinguish bricks by shape, but not colour.  For the Coltris, the opposite should have happened – labels would have distinguished bricks by colour but not shape.

Gary Lupyan has shown that naming categories of objects can affect your perception of those objects (Lupyan, G. (2008). The Conceptual Grouping Effect: Categories Matter (and named categories matter more). Cognition, 108, 566-577.).  My experiment looks into where those distinct category names came from in the first place.  Having said this, the experiment would have been more neat than illuminating.

Oh Well.

Population Size and Rates of Language Change

In previous posts, I’ve looked at the relationship between cultural evolution and demography (see here, here and here). As such, it makes sense to see if such methods are applicable in language which is, after all, a cultural product. So, having spent the last few days looking over the literature on language and demography, I found the following paper on population size and language change (free download). In it, the authors, Søren Wichmann and Eric Holman, use lexical data from WALS to test for an effect of the number of speakers on the rate of language change. Their general findings argue against a strong influence of  population size, with them instead opting for a model where the type of network influences change at a local level, through different degrees of connectivity between individuals. Here is the abstract:

Previous empirical studies of population size and language change have  produced  equivocal  results. We  therefore  address  the  question  with  a new set of lexical data from nearly one-half of the world’s languages. We first show that relative population sizes of modern languages can be extrapolated to ancestral languages, albeit with diminishing accuracy, up to several thousand years into the past. We then test for an effect of population against the null hypothesis that the ultrametric inequality is satisified by lexical distances among triples of related languages. The test shows mainly negligible effects of population, the exception being an apparently faster rate of change in the larger of two closely related variants. A possible explanation for the exception may be the influence on emerging standard (or cross-regional) variants from speakers who shift from different dialects to the standard. Our results strongly indicate that the sizes of speaker populations do not in and of themselves determine rates of language change. Comparison of this empirical  finding with previously published computer simulations suggests that the most plausible model  for  language  change  is  one  in  which  changes  propagate  on  a  local level in a type of network in which the individuals have different degrees of connectivity.

As I’m in the middle of several other things at the moment I don’t really have time to provide a thorough review of this paper. Having said that, I agree with their claim of population size being unlikely to account for rates of language change. I reckon their results would be stronger if they factored in population density. So those that are dense and large will change faster than those which are large and distributed. The main point being that population size and population density influence the degree of social interconnectivity. Nettle (1999), for instance, argues that “spreading an innovation over a tribe of 500 people is much easier and takes much less time than spreading one over five million people.” This is fairly reasonable if we are looking at the generation of a single innovation within each of these populations. However, if those 500 people are spread across a large distance, then their transmission chain is going to be stretched: effectively lowering the rate of transmission. The same applies for a population of five million individuals who are packed into a small area: Arguably, given the right conditions, we can arrive at a situation where a population of five million show greater levels of interconnectivity than 500. I think it’s this aspect, the level of social interconnectivity, which may be more relevant to the rate of language change (other things to test for, include: writing systems/literacy and inter-language contact).