Usage context and overspecification

A new issue of the Journal of Language Evolution has just appeared, including a paper by Peeter Tinits, Jonas Nölle, and myself on the influence of usage context on the emergence of overspecification. (It has actually been published online already a couple of weeks ago, and an earlier version of it was included in last year’s Evolang proceedings.) Some of the volunteers who participated in our experiment have actually been recruited via Replicated Typo – thanks to everyone who helped us out! Without you, this study wouldn’t have been possible.

I hope that I’ll find time to write a bit more about this paper in the near future, especially about its development, which might itself qualify as an interesting example of cultural evolution. Even though the paper just reports on a tiny experimental case study, adressing a fairly specific phenomenon, we discovered, in the process of writing, that each of the three authors had quite different ideas of how language works, which made the write-up process much more challenging than expected (but arguably also more interesting).

For now, however, I’ll just link to the paper and quote our abstract:

This article investigates the influence of contextual pressures on the evolution of overspecification, i.e. the degree to which communicatively irrelevant meaning dimensions are specified, in an iterated learning setup. To this end, we combine two lines of research: In artificial language learning studies, it has been shown that (miniature) languages adapt to their contexts of use. In experimental pragmatics, it has been shown that referential overspecification in natural language is more likely to occur in contexts in which the communicatively relevant feature dimensions are harder to discern. We test whether similar functional pressures can promote the cumulative growth of referential overspecification in iterated artificial language learning. Participants were trained on an artificial language which they then used to refer to objects. The output of each participant was used as input for the next participant. The initial language was designed such that it did not show any overspecification, but it allowed for overspecification to emerge in 16 out of 32 usage contexts. Between conditions, we manipulated the referential context in which the target items appear, so that the relative visuospatial complexity of the scene would make the communicatively relevant feature dimensions more difficult to discern in one of them. The artificial languages became overspecified more quickly and to a significantly higher degree in this condition, indicating that the trend toward overspecification was stronger in these contexts, as suggested by experimental pragmatics research. These results add further support to the hypothesis that linguistic conventions can be partly determined by usage context and shows that experimental pragmatics can be fruitfully combined with artificial language learning to offer valuable insights into the mechanisms involved in the evolution of linguistic phenomena.

In addition to our article, there’s also a number of other papers in the new JoLE issue that are well worth a read, including another Iterated Learning paper by Clay Beckner, Janet Pierrehumbert, and Jennifer Hay, who have conducted a follow-up on the seminal Kirby, Cornish & Smith (2008) study. Apart from presenting highly relevant findings, they also make some very interesting methodological points.

Empirical approaches to the study of language evolution (PBR Special Issue)

There is no shortage of special issues on language evolution in the current landscape of academic journals. However, probably none of the three upcoming special issues I know of (or the many more I don’t know of) will match Tecumseh Fitch’s special issue on “Empirical approaches in the study of Language Evolution” in “Psychonomic Bulletin and Review”, at least in terms of sheer size – by my count, the issue contains no less than 36 contributions by 39 mostly very well-known researchers.

The volume starts out with an impressive overview – which also serves as a review paper on recent advances in language evolution research – by Fitch himself. Like some of the other contributions, it is freely available with open access. As all contributions are available as “online first” papers at the moment and have not been assigned to an issue of the journal yet, the references section of the overview is also a good starting point for retrieving the other papers in the special issue.

Some of the papers are response articles to other contributions in the volume, which nicely highlights some key debates and open questions in the field. For example, both David Adger and Dan Bowling react to Simon Kirby’s paper on “Culture and biology in the emergence of linguistic structure”. Reviewing a large number of (both computational and behavioral) experiments using the Iterated Learning paradigm, including recent work on Bayesian Iterated Learning, Kirby argues that linguistic structure emerges as sets of behaviors (utterances) are transmitted through an informational bottleneck (the limited data available to the language learner) and the behaviors adapt to better pass through the bottleneck. According to Kirby, “[a]n overarching universal arising from this cultural process is that compressible sets of behaviours pass through the bottleneck more easily. If behaviours also need to be expressive then rich systematic structure appears to be the inevitable result.” Adger, however, argues that expressivity and compressibility are not sufficient to explain the emergence of structure. He points out that the systematicity of human languages is restricted in particular ways and that in the case of some grammatical phenomena, the simplest and most expressive option is logically possible but unattested in the world’s languages. He therefore argues that the human language capacity imposes strong constraints on language development, while the structures of particular languages arise in the way envisaged by the Iterated Learning model.

Kirby also discusses the relation between biological and cultural factors in language evolution. Probably the most far-reaching conclusion he draws from Iterated Learning models (in particular, from work by Bill Thompson et al.) is that the language faculty can only contain weak domain-specific constraints, while any hard constraints on the acquisition of language will almost certainly be domain-general. Bowling’s response is targeted at this aspect of Kirby’s theory. While being sympathetic with the emphasis on cultural evolution, he argues that it “fails to leave the nature-nurture dichotomy behind”, as constraints are identified as either cultural or biological. Unfortunately, Bowling doesn’t really have enough space to unfold this argument in more detail in this very short response paper.

A second paper in the special issue that is accompanied by a short commentary is Mark Johnson‘s “Marr’s levels and the minimalist program” (preprint). He discusses the question “what kind of simplicity is likely to be most related to the plausibility of an evolutionary event introducing a change to a cognitive system?” Obviously, this question bears important implications for Chomsky’s minimalist theory of language evolution, according to which a single mutation gave rise to the operation Merge, “a simple formal operation that yields the kinds of hierarchical structures found in human languages”. Johnson points out that just because a cognitive system is easy to describe does not necessarily mean that it is evolutionarily plausible. In order to approach the question “What kind of simplicity?”, he takes up David Marr’s levels of analysis of cognitive systems: the implementational level (the “hardware”), the algorithmic level (the representations and data structures involved), and the computational level (the goal(s) of the system; the information it manipulates; the constraints it must satisfy). He suggests that complexity of genomic encoding might be most closely related to complexity at the implementational level. The introduction of Merge, however, is complex at the computational level, while the changes on the other two levels could be quite complex. To strengthen the minimalist account of language evolution, then, one would have to either show systematic connections between the three levels, or demonstrate that a simple change to neural architecture can give rise to human language.

In her response paper, Amy Perfors (preprint) basically seconds Johnson’s position. However, she also points out that, from the perspective of Occam’s razor, computational simplicity might nevertheless be an important factor in model selection: “Because the more computationally complex a model or a theory is, the more difficult it is, plausibly, to represent or learn. For those reasons the simplicity of Merge is a theoretical asset when evaluating its cognitive plausibility.”

Kirby’s and Johnson’s papers and the respective responses can of course only give a glimpse of the thematic breadth of the special issue and the diversity of theoretical frameworks represented in the volume. Other topics include, e.g., the architecture of the “language-ready brain”, advances and missed opportunities in comparative research, and the role of different modalities in the evolution of language.

 

CfP: Interaction and Iconicity in the Evolution of Language

Following the ICLC theme session on “Cognitive Linguistics and the Evolution of Language” last year,  I’m guest-editing a Special Issue of the journal Interaction Studies together with Michael Pleyer, James Winters, and Jordan Zlatev. This volume, entitled “Interaction and Iconicity in the Evolution of Language: Converging Perspectives from Cognitive and Evolutionary Linguistics”, will focus on issues that emerged as common themes during the ICLC workshop.

Although many contributors to the theme session have already agreed to submit a paper, we would like to invite a limited number of additional contributions relevant to the topic of the volume. Here’s our Call for Papers.

Continue reading “CfP: Interaction and Iconicity in the Evolution of Language”

EvoLang Preview: Zombies, MMORPGs and Language Evolution

As readers of this blog will know, in evolutionary linguistics we use artificial languages in communication games all the time to investigate language evolution. However, these games, for the most part, remain very simple and confined to the lab. Massive multiplayer online role play games (MMORPGs)  may provide a new avenue for hypothesis testing in language evolution.

Below is just a case study of an MMORPG, so people can get an idea of what  we might be able to explore with a MMORPG set up. Though, this game was launched back in 2005, and was not designed as an experiment, so while there’s obviously experimental design issues, there’s still some pretty interesting things that have come out of it.

urbandead

Urban Dead is a zombie apocalypse MMORPG by Kevan Davis. You can either be a “survivor”, with your main aim being to kill zombies and to stay alive, or a “zombie”, who try to kill survivors and eat their brains. When a survivor is killed, they become a zombie. Zombies can also come back to life. So nearly everyone ends up being a zombie and a survivor at some point.  When alive, players can interact as normal with other players in the same location, using a text field. However, when a player becomes a zombie their ability to use language is restricted. The game manipulates the input text for zombies using a set of rules which include, but are not limited to:

  • all occurrences of e, i, o, u replaced with “r”
  • all characters other than “zhrgbmna .!?-” are deleted
  • lower-case “r” at the end of words replaced with “rh”
  • an “a” by itself will be replaced with “hra”

This constrained speech is called “death rattle”. As a result of these restrictions, several coded languages have emerged (e.g. Zombish and Zomese), which simply replace banned characters with combinations of allowed characters.

zombish

However, another language (Zamgrh) has also emerged, which uses a phonemic orthography. Zamgrh was originally bootstrapped by knowledge of English, but has since developed its own syntax, simple morphology and phonological rules. Some of these are similar to patterns found in pidgin languages, for example the use of “nah” before a verb as negation (1), and pronouns show no case, e.g. “ma zambah” can be used for “I” or “me” (1).

(1) Mah zambah nah     harm brazzarz.
    I          do  not hurt friends.

The lexicon of Zamgrh remains limited because of the constrained phonemic/orthographic limitations. Players are much more likely to use an existing word and allow context to dictate its meaning, e.g. using “babah” (baby) to mean “little”, “son”, “prince”, etc., which of course is facilitated by the context of the game being so small. Previously, small language populations have been hypothesised to use more context dependent language, because in tightly knit communities people have a lot of shared knowledge (see Wray & Grace, 2007). Zamgrh may help us shed light on whether context dependence is not only the result of shared knowledge, but also the result of smaller phoneme inventories allowing for less productivity in the language (interesting to think about in light of the correlations found by Hay & Bauer (2007) that small language populations have smaller phonemic inventories). There are many incidences in Zamgrh of established lexical items being adopted over new lexical inventions, even with knowledge of English facilitating new items being bootstrapped, almost certainly because of the constrained phonemic inventory. For example “barn” is used for any building, e.g. “Baghzbarn”, which refers to a warehouse, literally, “box barn” and “Agzbarn”, which refers to a fire station, literally, “axe barn”.

Death rattle may also have implications relevant to the size of inventories possible in different linguistic modalities, and how this might effect language evolution.

There currently exists a Zamgrh dictionary, as well as corpora containing some naturalistic zombie discourse and a small number of translated texts, including the poetry of Robert Burns (Rabar Barnz), Beowulf and some more contemporary texts, such as Rick Astley’s “Never gonna give you up” (Nabar Ganna Brang Gaa H!gh) and Queen’s “Bohemian Rhapsody” (Bahaman Rhabzag).

I have emailed the creator of the game, Kevan Davis, to see about the potential existence of a corpus of interactions as the language was developing, but this data is not available. Though, the data would be problematic anyway, as the the language seems to have developed quite a lot off-game by linguistics nerds, which is obviously not analogous to pidginisation at all. Also, the coded languages emerged much more quickly and more often than more pidgin-like languages, so any studies looking at using a similar paradigm would need to find ways to avoid this happening.

However, I think the game shows that with a bit more consideration for data collection and methodological problems, simple online games may become a useful tool for investigating mechanisms of pidginisation, linguistic bootstrapping, and conventionalisation.

I’ll be presenting some more thoughts on Zamgrh andMMORPGs at the Createvolang worksop at this year’s EvoLang.

References

Data and examples from the Urban Dead Wiki,  a list of contributors to the Zamgrh Project can be found here: http://wiki.urbandead.com/index.php/Category:Zombese_Linguists

Hay, J., & Bauer, L. (2007). Phoneme inventory size and population size. Language, 83(2), 388-400.

Wray, A. & Grace, G. (2007). The consequences of talking to strangers: Evolutionary corollaries of socio-cultural influences on linguistic form. Lingua 117 (3): 543-578.

Cognitive Linguistics and the Evolution of Language

On Tuesday, July 21st, this year’s International Cognitive Linguistics Conference will host a theme session on “Cognitive Linguistics and the Evolution of Language” co-organized by three Replicated Typo authors: Michael Pleyer, James Winters, and myself. In addition, two Replicated Typo bloggers are co-authors on papers presented in the theme session.

The general idea of this session goes back to previous work by James and Michael, who promoted the idea of integrating Cognitive Linguistics and language evolution research in several conference talks as well as in a 2014 paper – published, quite fittingly, in a journal called “Theoria et Historia Scientiarum”, as the very idea of combining these frameworks requires some meta-theoretical reflection. As both cognitive and evolutionary linguistics are in themselves quite heterogeneous frameworks, the question emerges what we actually mean when we speak of “cognitive” or “evolutionary” linguistics, respectively.

I might come back to this meta-scientific discussion in a later post. For now, I will confine myself to giving a brief overview of the eight talks in our session. The full abstracts can be found here.

In the first talk, Vyv Evans (Bangor) proposes a two-step scenario of the evolution of language, informed by concepts from Cognitive Linguistics in general and Langacker’s Cognitive Grammar in particular:

The first stage, logically, had to be a symbolic reference in what I term a words-to-world direction, bootstrapping extant capacities that Autralopithecines, and later ancestral Homo shared with the great apes. But the emergence of a grammatical capacity is also associated with a shift towards a words-to-words direction symbolic reference: words and other grammatical constructions can symbolically refer to other symbolic units.

Roz Frank (Iowa) then outlines “The relevance of a ‘Complex Adaptive Systems’ approach to ‘language’” – note the scarequotes. She argues that “the CAS approach serves to replace older historical linguistic notions of languages as ‘organisms’ and as ‘species’”.

Sabine van der Ham, Hannah Little, Kerem Eryılmaz, and Bart de Boer (Brussels) then talk about two sets of experiments investigating the role of individual learning biases and cultural transmission in shaping language, in a talk entitled “Experimental Evidence on the Emergence of Phonological Structure”.

In the next talk, Seán Roberts and Stephen Levinson (Nijmegen) provide experimental evidence for the hypothesis that “On-line pressures from turn taking constrain the cultural evolution of word order”. Chris Sinha’s talk, entitled “Eco-Evo-Devo: Biocultural synergies in language evolution”, is more theoretical in nature, but no less interesting. Starting from the hypothesis that “many species construct “artefactual” niches, and language itself may be considered as a transcultural component of the species-specific human biocultural niche”, he argues that

Treating language as a biocultural niche yields a new perspective on both the human language capacity and on the evolution of this capacity. It also enables us to understand the significance of language as the symbolic ground of the special subclass of symbolic cognitive artefacts.

Arie Verhagen (Leiden) then discusses the question if public and private communication are “Stages in the Evolution of Language”.  He argues against Tomasello’s idea that ““joint” intentionality emerged first and evolved into what is essentially still its present state, which set the stage for the subsequent evolution of “collective” intentionality” and instead defends the view that

these two kinds of processes and capacities evolved ‘in tandem’: A gradual increase in the role of culture (learned patterns of behaviour) produced differences and thus competition between groups of (proto-)humans, which in turn provided selection pressures for an increased capability and motivation of individuals to engage in collaborative activities with others.

James Winters (Edinburgh) then provides experimental evidence that “Linguistic systems adapt to their contextual niche”, addressing two major questions with the help of an artificial-language communication game:

(i) To what extent does the situational context influence the encoding of features in the linguistic system? (ii) How does the effect of the situational context work its way into the structure of language?

His results “support the general hypothesis that language structure adapts to the situational contexts in which it is learned and used, with short-term strategies for conveying the intended meaning feeding back into long-term, system-wider changes.”

The final talk, entitled “Communicating events using bodily mimesis with and without vocalization” is co-authored by Jordan Zlatev, Sławomir Wacewicz, Przemysław Żywiczyński,  andJoost van de Weijer (Lund/Torun). They introduce an experiment on event communication and discuss to what extent the greater potential for iconic representation in bodily reenactment compared to in vocalization might lend support for a “bodily mimesis hypothesis of language origins”.

In the closing session of the workshop, this highly promising array of papers is discussed with one of the “founding fathers” of modern language evolution research, Jim Hurford (Edinburgh).

But that’s not all: Just one coffee break after the theme session, there will be a panel on “Language and Evolution” in the general session of the conference, featuring papers by Gareth Roberts & Maryia Fedzechkina; Jonas Nölle; Carmen Saldana, Simon Kirby & Kenny Smith; Yasamin Motamedi, Kenny Smith, Marieke Schouwstra & Simon Kirby; and Andrew Feeney.

Language as a multimodal phenomenon

The issue of multimodality has become a widely discussed topic in several branches of linguistics and especially in research on the evolution of language. Now, a special issue of the “Philosophical Transactions of the Royal Society B” has been dedicated to “Language as a multimodal phenomenon”. The issue, edited by Gabriella Vigliocco, Pamela Perniss, and David Vinson, features a variety of interesting papers by outstanding scholars from different fields such as gesture research, signed language research, neurolinguistics, and evolutionary linguistics.

For example, Susan Goldin-Meadow discusses “what the manual modality reveals about language, learning and cognition”, arguing that, in child language acquisition, manual gestures “precede, and predict, the acquisition of structures in speech”.

Ulf Liszkowski addresses the question of how infants communicate before they have acquired a language, and Aslı Özyürek reviews neuroscientific findings on “Hearning and seeing meaning in speech and gesture”. Jeremy Skipper discusses “how auditory cortex hears context during speech perception”, and Stephen Levinson and Judith Holler, in a paper entitled “The origin of human multi-modal communication”,  talk about “the different roles that the different modalities play in human communication, as well as how they function as one integrated system despite their different roles and origins.”

Martin Sereno, in his opinion piece on the “Origin of  symbol-using systems”, argues that we have to distinguish “the origin of a system capable of evolution from the subsequent evolution that system becomes capable of”. According to Sereno,

“Human language arose on a substrate of a system already capable of Darwinian evolution; the genetically supported uniquely human ability to learn a language reflects a key contact point between Darwinian evolution and language. Though implemented in brains generated by DNA symbols coding for protein meaning, the second higher-level symbol-using system of language now operates in a world mostly decoupled from Darwinian evolutionary constraints.”

Padraic Monaghan, Richard C. Shillcock, Morten H. Christiansen, and Simon Kirby address the question “How arbitrary is language?” Drawing on a large-scale corpus analysis, they show that

“sound–meaning mappings are more systematic than would be expected by chance. Furthermore, this systematicity is more pronounced for words involved in the early stages of language acquisition and reduces in later vocabulary development.”

Mutsumi Imai and Sotaro Kita propose a “sound symbolism bootstrapping hypothesis for language acquisition and language evolution”, arguing that “sound symbolism helps infants and toddlers associate speech sounds with their referents to establish a lexical representation” and that sound symbolism might be deeply related to language evolution.

Karen Emmorey discusses the role of iconicity in sign language grammar and processing, and in the final paper, Pamela Perniss and Gabriella Vigliocco argue that ” iconicity in face-to-face communication (spoken and signed) is a powerful vehicle for bridging between language and human sensori-motor experience, and, as such, iconicity provides a key to understanding language evolution, development and processing.”

The special issue is available here. Some of the papers are open access, all others can be accessed freely until October 19th ( User name: language; Password: tb1651 – since this information was distributed by the Royal Sociaty via several mailing lists, I guess I’m free to share it here).

 

Vyv Evans: The Human Meaning-Making Engine

If you read my last post here at Replicated Typo to the very end, you may remember that I promised to recommend a book and to return to one of the topics of this previous post. I won’t do this today, but I promise I will catch up on it in due time.

What I just did – promising something – is a nice example for one of the two functions of language which Vyvyan Evans from Bangor University distinguished in his talk on “The Human Meaning-Making Engine” yesterday at the UK Cognitive Linguistics Conference. More specifically, the act of promising is an example for the interactive function of language, which is of course closely intertwined with its symbolic function. Evans proposed two different sources for this two functions. The interactive function, he argued, arises from the human instinct for cooperation, whereas meaning arises from the interaction between the linguistic and the conceptual system. While language provides the “How” of meaning-making, the conceptual system provides the “What”. Evans used some vivid examples (e.g. this cartoon exemplifying nonverbal communication) to make clear that communication is not contingent on language. However, “language massively amplifies our communicative potential.” The linguistic system, he argued, has evolved as an executive control system for the conceptual system. While the latter is broadly comparable with that of other animals, especially great apes, the linguistic system is uniquely human. What makes it unique, however, is not the ability to refer to things in the world, which can arguably be found in other animals, as well. What is uniquely human, he argued, is the ability to symbolically refer in a sign-to-sign (word-to-word) direction rather than “just” in a sign-to-world (word-to-world) direction.  Evans illustrated this “word-to-word” direction with Hans-Jörg Schmid’s (e.g.  2000; see also here)  work on “shell nouns”, i.e. nouns “used in texts to refer to other passages of the text and to reify them and characterize them in certain ways.” For instance, the stuff I was talking about in the last paragraph would be an example of a shell noun.

According to Evans, the “word-to-word” direction is crucial for the emergence of e.g. lexical categories and syntax, i.e. the “closed-class” system of language. Grammaticalization studies indicate that the “open-class” system of human languages is evolutionarily older than the “closed-class” system, which is comprised of grammatical constructions (in the broadest sense). However, Evans also emphasized that there is a lot of meaning even in closed-class constructions, as e.g. Adele Goldberg’s work on argument structure constructions shows: We can make sense of a sentence like “Someone somethinged something to someone” although the open-class items are left unspecified.

Constructions, he argued, index or cue simulations, i.e. re-activations of body-based states stored in cortical and subcortical brain regions. He discussed this with the example of the cognitive model for Wales: We know that Wales is a geographical entity. Furthermore, we know that “there are lots of sheep, that the Welsh play Rugby, and that they dress in a funny way.” (Sorry, James. Sorry, Sean.) Oh, and “when you’re in Wales, you shouldn’t say, It’s really nice to be in England, because you will be lynched.”

On a more serious note, the cognitive models connected to closed-class constructions, e.g. simple past -ed or progressive -ing, are of course much more abstract but can also be assumed to arise from embodied simulations (cf. e.g. Bergen 2012). But in addition to the cognitive dimension, language of course also has a social and interactive dimension drawing on the apparently instinctive drive towards cooperative behaviour. Culture (or what Tomasello calls “collective intentionality”)  is contigent on this deep instinct which Levinson (2006) calls the “human interaction engine”. Evans’ “meaning-making engine” is the logical continuation of this idea.

Just like Evans’ theory of meaning (LCCM theory), his idea of the “meaning-making engine” is basically an attempt at integrating a broad variety of approaches into a coherent model. This might seem a bit eclectic at first, but it’s definitely not the worst thing to do, given that there is significant conceptual overlap between different theories which, however, tends to be blurred by terminological incongruities. Apart from Deacon’s (1997) “Symbolic Species” and Tomasello’s work on shared and joint intentionality, which he explicitly discussed, he draws on various ideas that play a key role in Cognitive Linguistics. For example, the distinction between open- and closed-class systems features prominently in Talmy’s (2000) Cognitive Semantics, as does the notion of the human conceptual system. The idea of meaning as conceptualization and embodied simulation of course goes back to the groundbreaking work of, among others, Lakoff (1987) and Langacker (1987, 1991), although empirical support for this hypothesis has been gathered only recently in the framework of experimental semantics (cf. Matlock & Winter forthc. – if you have an account at academia.edu, you can read this paper here). All in all, then, Evans’ approach might prove an important further step towards integrating Cognitive Linguistics and language evolution research, as has been proposed by Michael and James in a variety of talks and papers (see e.g. here).

Needless to say, it’s impossible to judge from a necessarily fairly sketchy conference presentation if this model qualifies as an appropriate and comprehensive account of the emergence of meaning. But it definitely looks promising and I’m looking forward to Evans’ book-length treatment of the topics he touched upon in his talk. For now, we have to content ourselves with his abstract from the conference booklet:

In his landmark work, The Symbolic Species (1997), cognitive neurobiologist Terrence Deacon argues that human intelligence was achieved by our forebears crossing what he terms the “symbolic threshold”. Language, he argues, goes beyond the communicative systems of other species by moving from indexical reference – relations between vocalisations and objects/events in the world — to symbolic reference — the ability to develop relationships between words — paving the way for syntax. But something is still missing from this picture. In this talk, I argue that symbolic reference (in Deacon’s terms), was made possible by parametric knowledge: lexical units have a type of meaning, quite schematic in nature, that is independent of the objects/entities in the world that words refer to. I sketch this notion of parametric knowledge, with detailed examples. I also consider the interactional intelligence that must have arisen in ancestral humans, paving the way for parametric knowledge to arise. And, I also consider changes to the primate brain-plan that must have co-evolved with this new type of knowledge, enabling modern Homo sapiens to become so smart.

 

References

Bergen, Benjamin K. (2012): Louder than Words. The New Science of How the Mind Makes Meaning. New York: Basic Books.

Deacon, Terrence W. (1997): The Symbolic Species. The Co-Evolution of Language and the Brain. New York, London: Norton.

Lakoff, George (1987): Women, Fire, and Dangerous Things. What Categories Reveal about the Mind. Chicago: The University of Chicago Press.

Langacker, Ronald W. (1987): Foundations of Cognitive Grammar. Vol. 1. Theoretical Prerequisites. Stanford: Stanford University Press.

Langacker, Ronald W. (1991): Foundations of Cognitive Grammar. Vol. 2. Descriptive Application. Stanford: Stanford University Press.

Levinson, Stephen C. (2006): On the Human “Interaction Engine”. In: Enfield, Nick J.; Levinson, Stephen C. (eds.): Roots of Human Sociality. Culture, Cognition and Interaction. Oxford: Berg, 39–69.

Matlock, Teenie & Winter, Bodo (forthc): Experimental Semantics. In: Heine, Bernd; Narrog, Heiko (eds.): The Oxford Handbook of Linguistic Analysis. 2nd ed. Oxford: Oxford University Press.

Schmid, Hans-Jörg (2000): English Abstract Nouns as Conceptual Shells. From Corpus to Cognition. Berlin, New York: De Gruyter (Topics in English Linguistics, 34).

Talmy, Leonard (2000): Toward a Cognitive Semantics. 2 vol. Cambridge, Mass: MIT Press.

 

Syntax came before phonology?

ResearchBlogging.org
A new paper has just appeared in the proceedings of the royal society B entitled, “Language evolution: syntax before phonology?” by Collier et al.

The abstract is here:

Phonology and syntax represent two layers of sound combination central to language’s expressive power. Comparative animal studies represent one approach to understand the origins of these combinatorial layers. Traditionally, phonology, where meaningless sounds form words, has been considered a simpler combination than syntax, and thus should be more common in animals. A linguistically informed review of animal call sequences demonstrates that phonology in animal vocal systems is rare, whereas syntax is more widespread. In the light of this and the absence of phonology in some languages, we hypothesize that syntax, present in all languages, evolved before phonology.

This is essentially a paper about the distinction between combinatorial and compositional structure and the emergence narrative of duality of patterning. I wrote a post about this a few months ago, see here. The paper focusses on evidence from non-human animals and also evidence from human languages, including Al-Sayyid Bedouin Sign Language, looking at differences and similarities between human abilities and those of other animals.

Peter Marler outlined different types of call combinations found in animal communication by making a distinction between ‘Phonological syntax’ (combinatorial structure), which he claims is widespread in animals, and ‘lexical syntax’ (compositional structure), which he claims  have yet to be described in animals (I can’t find a copy of the 1998 paper which Collier et al. cite, but he talks about this on his homepage here). Collier et al. however, disagree and review several animal communication systems which they claim fall under a definition of “lexical syntax”.

They start by defining what they mean by the different levels of structure within language (I talk about this here).  They present the following relatively uncontroversial table:

inline-graphic-1

 Evidence from non-human species

The paper reviews evidence from 4 species; 1) Winter wrens (though you could arguably lump all birdsong in with their analysis for this one),  2) Campbell monkeys, 3) Putty-nosed monkeys and 4) Banded mongooses.

1) Birdsong is argued to be combinatorial, as whatever the combination of notes or syllables, the songs always have the same purpose and so the “meaning” can not be argued to be a result of the combination.

2) In contrast to  Marler, the authors argue that Campbell monkeys have compositional structure in their calls. The monkeys give a ‘krak’ call when there is a leopard near, and a ‘hok’ call when there is an eagle. Interestingly, they can add an ‘-oo’ to either of these calls change their meanings. ‘Krak-oo’ denotes any general disturbance and ‘hok-oo’ denotes a disturbance in the canopy. One can argue then that this “-oo” has the same meaning of “disturbance”, no matter what construction it is in, and “hok” generally means “above”, hinting at compositional structure.

3) The authors also discuss Putty-nosed monkeys, which were also discussed in this paper by Scott-Philips and Blythe (again, discussed here). While Scott-Philips and Blythe arrive at the conclusion that the calls of putty-nosed monkeys are combinatorial (i.e. the combined effect of two signals does not amount to the combined meaning of those two signals):

F1.medium

“Applied to the putty-nosed monkey system, the symbols in this figure are: a, presence of eagles; b, presence of leopards; c, absence of food; A, ‘pyow’; B, ‘hack’ call; C = A + B ‘pyow–hack’; X, climb down; Y, climb up; Z ≠ X + Y, move to a new location. Combinatorial communication is rare in nature: many systems have a signal C = A + B with an effect Z = X + Y; very few have a signal C = A + B with an effect Z ≠ X + Y.”

However, Collier et al. argue this example is not necessarily combinatorial, as the pyow-hack sequences could be interpreted as idiomatic, or have much more abstract meanings such as ‘move-on-ground’ and ‘move-in-air’, however in order for this analysis to hold weight, one must assume the monkeys are able to use contextual information to make inferences about meaning, which is a pretty controversial claim. However, Collier et al. argue that it shouldn’t be considered so far-fetched given the presence of compositionality in the calls of Campbell monkeys.

4) The author’s also  discuss Branded Mongooses who emit close calls while looking for food.  Their calls begin with an initial noisy segment that encodes the caller’s identity, which is stable across all contexts. In searching and moving contexts, there is a second tonal harmonic that varies in length consistently with context. So one could argue that identity and context are being systematically encoded into their call sequences with one to one mappings between signal and meaning.

(One can’t help but think that a discussion of the possibility of compositionality in bee dances is a missed opportunity here.)

Syntax before phonology?

The authors use the above (very sketchy and controversial) examples of compositional structure to make the case that syntax came before phonology. Indeed, there exist languages where a level of phonological patterning does not exist (the go-to example being Al-Sayyid Bedouin Sign Language). However, I would argue that the emergence of combinatoriality is, in large part, the result of the modality one is using to produce language. My current work is looking at how the size and dimensionality of a signal space, as well as how mappable that signal space is to a meaning space (to enable iconicity), can massively effect the emergence of a combinatorial system, and I don’t think it’s crazy to suggest the modality used will effect the emergence narrative for duality of patterning.

Collier et al. attempt to use some evidence from spoken languages with large inventories, or instances where single phonemes in spoken languages are highly context-dependant meaningful elements, to back up a story where syntax might have come first in spoken language. But given the physical and perceptual constraints of a spoken system, it’s really hard for me to imagine how a productive syntactic system could have existed without a level of phonological patterning. The paper makes the point that it is theoretically possible (which is really interesting), but I’m not convinced that it is likely (though this paper by Juliette Blevins is well worth a read).

Whilst I don’t disagree with Collier et al.’s conclusion that phonological patterning is most likely the product of cultural evolution, I feel like the physical constraints of a linguistic modality will massively effect the emergence of such a system, and arguing for an over-arching emergence story without consideration for non-cognitive factors is an over-sight. 

References

Collier, K., Bickel, B., van Schaik, C., Manser, M., & Townsend, S. (2014). Language evolution: syntax before phonology? Proceedings of the Royal Society B: Biological Sciences, 281 (1788), 20140263-20140263 DOI: 10.1098/rspb.2014.0263

Why Disagree? Some Critical Remarks on the Integration Hypothesis of Human Language Evolution

Shigeru Miyagawa, Shiro Ojima, Robert Berwick and Kazuo Okanoya have recently published a new paper in Frontiers in Psychology, which can be seen as a follow-up to the 2013 Frontiers paper by Miyagawa, Berwick and Okanoya (see Hannah’s post on this paper). While the earlier paper introduced what they call the “Integration Hypothesis of Human Language Evolution”, the follow-up paper seeks to provide empirical evidence for this theory and discusses potential challenges to the Integration Hypothesis.

The basic idea of the Integration Hypothesis, in a nutshell, is this: “All human language sentences are composed of two meaning layers” (Miyagawa et al. 2013: 2), namely “E” (for “expressive”) and “L” (for “lexical”). For example, sentences like “John eats a pizza”, “John ate a pizza”, and “Did John eat a pizza?” are supposed to have the same lexical meaning, but they vary in their expressive meaning. Miyagawa et al. point to some parallels between expressive structure and birdsong on the one hand and lexical structure and the alarm calls of non-human primates on the other. More specifically, “birdsongs have syntax without meaning” (Miyagawa et al. 2014: 2), whereas alarm calls consist of “isolated uttered units that correlate with real-world references” (ibid.). Importantly, however, even in human language, the Expression Structure (ES) only admits one layer of hierarchical structure, while the Lexical Structure (LS) does not admit any hierarchical structure at all (Miyagawa et al. 2013: 4). The unbounded hierarchical structure of human language (“discrete infinity”) comes about through recursive combination of both types of structure.

This is an interesting hypothesis (“interesting” being a convenient euphemism for “well, perhaps not that interesting after all”). Let’s have a closer look at the evidence brought forward for this theory.

Miyagawa et al. “focus on the structures found in human language” (Miyagawa et al. 2014: 1), particularly emphasizing the syntactic structure of sentences and the internal structure of words. In a sentence like “Did John eat pasta?”, the lexical items John, eat, and pasta constitute the LS, while the auxiliary do, being a functional element, is seen as belonging to the expressive layer. In a more complex sentence like “John read the book that Mary wrote”, the VP and NP notes are allocated to the lexical layer, while the DP and CP nodes are allocated to the expressive layer.

Fig. 9 from Miyagawa et al. (2014), illustrating how unbounded hierarchical structure emerges from recursive combination of E- and L-level structures
Fig. 9 from Miyagawa et al. (2014), illustrating how unbounded hierarchical structure emerges from recursive combination of E- and L-level structures

As pointed out above, LS elements cannot directly combine with each other according to Miyagawa et al. (the ungrammaticality of e.g. John book and want eat pizza is taken as evidence for this), while ES is restricted to one layer of hierarchical structure. Discrete infinity then arises through recursive application of two rules:

(i) EP →  E LP
(ii) LP → L EP
Rule (i) states that the E category can combine with LP to form an E-level structure. Rule (ii) states that the L category can combine with an E-level structure to form an L-level structure. Together, these two rules suffice to yield arbitrarily deep hierarchical structures.

The alternation between lexical and expressive elements, as exemplified in Figure (3) from the 2014 paper (= Figure 9 from the 2013 paper, reproduced above), is thus essential to their theory since they argue that “inside E and L we only find finite-state processes” (Miyagawa et al. 2014: 3). Several phenomena, most notably Agreement and Movement, are explained as “linking elements” between lexical and functional heads (cf. also Miyagawa 2010). A large proportion of the 2014 paper is therefore dedicated to phenomena that seem to argue against this hypothesis.

For example, word-formation patterns that can be applied recursively seem to provide a challenge for the theory, cf. example (4) in the 2014 paper:

(4) a. [anti-missile]
b. [anti-[anti-missile]missile] missile

The ostensible point is that this formation can involve center embedding, which would constitute a non-finite state construction.

However, they propose a different explanation:

When anti– combines with a noun such as missile, the sequence anti-missile is a modifier that would modify a noun with this property, thus, [anti-missile]-missile,  [anti-missile]-defense. Each successive expansion forms via strict adjacency, (…) without the need to posit a center embedding, non-regular grammar.

Similarly, reduplication is re-interpreted as a finite state process. Furthermore, they discuss N+N compounds, which seems to violate “the assumption that L items cannot combine directly — any combination requires intervention from E.” However, they argue that the existence of linking elements in some languages provides evidence “that some E element does occur between the two L’s”. Their example is German Blume-n-wiese ‘flower meadow’, others include Freundeskreis ‘circle of friends’ or Schweinshaxe ‘pork knuckle’. It is commonly assumed that linking elements arose from grammatical markers such as genitive -s, e.g. Königswürde ‘royal dignity’ (from des Königs Würde ‘the king’s dignity’). In this example, the origin of the linking element is still transparent. The -es- in Freundeskreis, by contrast, is an example of a so-called unparadigmatic linking element since it literally translates to ‘circle of a friend’. In this case as well as in many others, the linking element cannot be traced back directly to a grammatical affix. Instead, it seems plausible to assume that the former inflectional suffix was reanalyzed as a linking element from the paradigmatic cases and subsequently used in other compounds as well.

To be sure, the historical genesis of German linking elements doesn’t shed much light on their function in present-day German, which is subject to considerable debate. Keeping in mind that these items evolved gradually however raises the question how the E and L layers of compounds were linked in earlier stages of German (or any other language that has linking elements). In addition, there are many German compounds without a linking element, and in other languages such as English, “linked” compounds like craft-s-man are the exception rather than the rule. Miyagawa et al.’s solution seems a bit too easy to me: “In the case of teacup, where there is no overt linker, we surmise that a phonologically null element occurs in that position.”

As an empiricist, I am of course very skeptical towards any kind of null element. One could possibly rescue their argument by adopting concepts from Construction Grammar and assigning E status to the morphological schema [N+N], regardless of the presence or absence of a linking element, but then again, from a Construction Grammar point of view, assuming a fundamental dichotomy between E and L structures doesn’t make much sense in the first place. That said, I must concede that the E vs. L distinction reflects basic properties of language that play a role in any linguistic theory, but especially in Construction Grammar and in Cognitive Linguistics. On the one hand, it reflects the rough distinction between “open-class” and “closed-class” items, which plays a key role in Talmy’s (2000) Cognitive Semantics and in the grammaticalization literature (cf. e.g. Hopper & Traugott 2003). As many grammaticalization studies have shown, most if not all closed-class items are “fossils” of open-class items. The abstract concepts they encode (e.g. tense or modality) are highly relevant to our everyday experience and, consequently, to our communication, which is why they got grammaticized in the first place. As Rose (1973: 516) put it, there is no need for a word-formation affix deriving denominal verbs meaning “grasp NOUN in the left hand and shake vigorously while standing on the right foot in a 2 ½ gallon galvanized pail of corn-meal-mush”. But again, being aware of the historical emergence of these elements begs the question if a principled distinction between the meanings of open-class vs. closed-class elements is warranted.

On the other hand, the E vs. L distinction captures the fundamental insight that languages pair form with meaning. Although they are explicitly talking about the “duality of semantics“, Miyagawa et al. frequently allude to formal properties of language, e.g. by linking up syntactic strutures with the E layer:

The expression layer is similar to birdsongs; birdsongs have specific patterns, but they do not contain words, so that birdsongs have syntax without meaning (Berwick et al., 2012), thus it is of the E type.

While the “expression” layer thus seems to account for syntactic and morphological structures, which are traditionally regarded as purely “formal” and meaningless, the “lexical” layer captures the referential function of linguistic units, i.e. their “meaning”. But what is meaning, actually? The LS as conceptualized by Miyagawa et al. only covers the truth-conditional meaning of sentences, or their “conceptual content”, as Langacker (2008) calls it. From a usage-based perspective, however, “an expression’s meaning consists of more than conceptual content – equally important to linguistic semantics is how that content is shaped and construed.” (Langacker 2002: xv) According to the Integration Hypothesis, this “construal” aspect is taken care of by closed-class items belonging to the E layer. However, the division of labor envisaged here seems highly idealized. For example, tense and modality can be expressed using open-class (lexical) items and/or relying on contextual inference, e.g. German Ich gehe morgen ins Kino ‘I go to the cinema tomorrow’.

It is a truism that languages are inherently dynamic, exhibiting a great deal of synchronic variation and diachronic change. Given this dynamicity, it seems hard to defend the hypothesis that a fundamental distinction between E and L structures which cannot combine directly can be found universally in the languages of the world (which is what Miyagawa et al. presuppose). We have already seen that in the case of compounds, Miyagawa et al. have to resort to null elements in order to uphold their hypothesis. Furthermore, it seems highly likely that some of the “impossible lexical structures” mentioned as evidence for the non-combinability hypothesis are grammatical at least in some creole languages (e.g. John book, want eat pizza).

In addition, it seems somewhat odd that E- and L-level structures as “relics” of evolutionarily earlier forms of communication are sought (and expected to be found) in present-day languages, which have been subject to millennia of development. This wouldn’t be a problem if the authors were not dealing with meaning, which is not only particularly prone to change and variation, but also highly flexible and context-dependent. But even if we assume that the existence of E-layer elements such as affixes and other closed-class items draws on innate dispositions, it seems highly speculative to link the E layer with birdsong and the L layer with primate calls on semantic grounds.

The idea that human language combines features of birdsong with features of primate alarm calls is certainly not too far-fetched, but the way this hypothesis is defended in the two papers discussed here seems strangely halfhearted and, all in all, quite unconvincing. What is announced as “providing empirical evidence” turns out to be a mostly introspective discussion of made-up English example sentences, and if the English examples aren’t convincing enough, the next best language (e.g. German) is consulted. (To be fair, in his monograph, Miyagawa (2010) takes a broader variety of languages into account.) In addition, much of the discussion is purely theory-internal and thus reminiscent of what James has so appropriately called “Procrustean Linguistics“.

To their credit, Miyagawa et al. do not rely exclusively on theory-driven analyses of made-up sentences but also take some comparative and neurological studies into account. Thus, the Integration Hypothesis – quite unlike the “Mystery” paper (Hauser et al. 2014) co-authored by Berwick and published in, you guessed it, Frontiers in Psychology (and insightfully discussed by Sean) – might be seen as a tentative step towards bridging the gap pointed out by Sverker Johansson in his contribution to the “Perspectives on Evolang” section in this year’s Evolang proceedings:

A deeper divide has been lurking for some years, and surfaced in earnest in Kyoto 2012: that between Chomskyan biolinguistics and everybody else. For many years, Chomsky totally dismissed evolutionary linguistics. But in the past decade, Chomsky and his friends have built a parallel effort at elucidating the origins of language under the label ‘biolinguistics’, without really connecting with mainstream Evolang, either intellectually or culturally. We have here a Kuhnian incommensurability problem, with contradictory views of the nature of language.

On the other hand, one could also see the Integration Hypothesis as deepening the gap since it entirely draws on generative (or “biolinguistic”) preassumptions about the nature of language which are not backed by independent empirical evidence. Therefore, to conclusively support the Integration Hypothesis, much more evidence from many different fields would be necessary, and the theoretical preassumptions it draws on would have to be scrutinized on empirical grounds, as well.

References

Hauser, Marc D.; Yang, Charles; Berwick, Robert C.; Tattersall, Ian; Ryan, Michael J.; Watumull, Jeffrey; Chomsky, Noam; Lewontin, Richard C. (2014): The Mystery of Language Evolution. In: Frontiers in Psychology 4. doi: 10.3389/fpsyg.2014.00401

Hopper, Paul J.; Traugott, Elizabeth Closs (2003): Grammaticalization. 2nd ed. Cambridge: Cambridge University Press.

Johansson, Sverker: Perspectives on Evolang. In: Cartmill, Erica A.; Roberts, Séan; Lyn, Heidi; Cornish, Hannah (eds.) (2014): The Evolution of Language. Proceedings of the 10th International Conference. Singapore: World Scientific, 14.

Langacker, Ronald W. (2002): Concept, Image, and Symbol. The Cognitive Basis of Grammar. 2nd ed. Berlin, New York: De Gruyter (Cognitive Linguistics Research, 1).

Langacker, Ronald W. (2008): Cognitive Grammar. A Basic Introduction. Oxford: Oxford University Press.

Miyagawa, Shigeru (2010): Why Agree? Why Move? Unifying Agreement-Based and Discourse-Configurational Languages. Cambridge: MIT Press (Linguistic Inquiry, Monographs, 54).

Miyagawa, Shigeru; Berwick, Robert C.; Okanoya, Kazuo (2013): The Emergence of Hierarchical Structure in Human Language. In: Frontiers in Psychology 4. doi 10.3389/fpsyg.2013.00071

Miyagawa, Shigeru; Ojima, Shiro; Berwick, Robert C.; Okanoya, Kazuo (2014): The Integration Hypothesis of Human Language Evolution and the Nature of Contemporary Languages. In: Frontiers in Psychology 5. doi 10.3389/fpsyg.2014.00564

Rose, James H. (1973): Principled Limitations on Productivity in Denominal Verbs. In: Foundations of Language 10, 509–526.

Talmy, Leonard (2000): Toward a Cognitive Semantics. 2 vol. Cambridge, Mass: MIT Press.

P.S.: After writing three posts in a row in which I critizised all kinds of studies and papers, I herby promise that in my next post, I will thoroughly recommend a book and return to a question raised only in passing in this post.  [*suspenseful cliffhanger music*]

Defining iconicity and its repercussions in language evolution

There was an awful lot of talk about iconicity at this year’s EvoLang conference (as well as in previous years), and its ability to bootstrap communication systems and solve symbol grounding problems, and this has lead to talk on its possible role in the emergence of human language. Some work has been more sceptical than other’s about the role of iconicity, and so I thought it would be useful to do a wee overview of some of the talks I saw in relation to how different presenters define iconicity (though this is by no stretch a comprehensive overview).

As with almost everything, how people define iconicity differs across studies. In a recent paper, Monaghan, Shillcock, Christiansen & Kirby (2014) identify two forms of iconicity in language; absolute iconicity and relative iconicity. Absolute iconicity is where some linguistic feature imitates a referent, e.g. onomatopoeia or gestural pantomime. Relative iconicity is where there is a signal-meaning mapping or there is a correlation between similar signals and similar meanings. Relative iconicity is usually only clear when the whole meaning and signal spaces can be observed together and systematic relations can be observed between them.

Liz Irvine gave a talk on the core assumption that iconicity played a big role in in bootstrapping language. She teases apart the distinction above by calling absolute iconicity, “diagrammatic iconicity” and relative iconicity, “imagic iconicity”. “Imagic iconicity” can be broken down even further and can be measured on a continuum either in terms of how signals are used and interpreted by language users, or simply by objectively looking at meaning-signal mappings where signs can be non-arbitrary, but not necessarily treated as iconic by language users. Irvine claims that this distinction is important in accessing the role of iconicity in the emergence of language. She argues that diagrammatic or absolute iconicity may aid adults in understanding new signs, but it doesn’t necessarily aid early language learning in infants. Whereas imagic, or relative iconicity, is a better candidate to aid language acquisition and language emergence, where language users do not interpret the signal-meaning mappings explicitly as being iconic, even though they are non-arbitrary.

Irvine briefly discusses that ape gestures are not iconic from the perspective of their users. Marcus Perlman, Nathaniel Clark and Joanne A. Tanner presented work on whether iconicity exists in ape gesture. They define iconicity as being gestures which in any way resemble or depict their meanings but break down these gestures into pantomimed actions, directive touches and visible directives, which are all arguably examples of absolute iconicity. Following from Irvine’s arguments, this broad definition of iconicity may not be so useful when drawing up scenarios for language evolution, and the authors try to provide more detailed and nuanced analysis drawing from the interpretation of signs from the ape’s perspective. Theories which currently exist on iconicity in ape gesture maintain that any iconicity is an artefact of the gesture’s development through inheritance and ritualisation. However, the authors argue that these theories do not currently account for the variability and creativity seen in iconic ape gestures which may help frame iconicity from the perspective of its user.

It’s difficult to analyse iconicity from an ape’s perspective, however, it should be much easier to get at how human’s perceive and interpret different types of iconicity via experiments. I think that experimental design can help get at this, but also analysis from a user perspective from post-experimental questionnaires or even post-experimental experiments (where naive participants are asked to rate to what degree a sign represents a meaning).

Gareth Roberts and Bruno Galantucci presented a study where their hypothesis was that a modality’s capacity for iconicity may inhibit the emergence of combinatorial structure (phonological patterning) in a system. This hypothesis may explain why emerging sign languages, which have more capacity for iconicity than spoken languages, can have fully expressive systems without a level of combinatorial structure (see here). They used the now famous paradigm from Galantucci’s 2005 experiment here. They asked participants to communicate a variety of meanings which were either lines, which could be represented through absolute iconicity with the modality provided, or circles which were various shades of green, which could not be iconically represented. The experiment showed that indeed, the signals used for circles were made up from combinatorial elements where the lines retained iconicity throughout the experiment. This is a great experiment and I really like it, however, I worry that it is only looking at two extreme ends of the iconicity continuum, and has not considered the effects of relative iconicity, or nuances of signal-meaning relations.  In de Boer and Verhoef (2012), a mathematical model shows that shared topology between signal and meaning spaces will generate an iconic system with signal-meaning mapping, but mismatched topologies will generate systems with conventionalised structure. I think it is important that experimental work now looks into more slight differences between signal and meaning spaces and the effects these differences will have on structure in emerging linguistic systems in the lab, and also how participant’s interpretation of any iconicity or structure in a system effects the nature of that iconicity or structure. I’m currently running some experiments exploring this myself, so watch this space!

References

Where possible, I’ve linked to studies as I’ve cited them.

All other studies cited are included in Erica A. Cartmill, Seán Roberts, Heidi Lyn & Hannah Cornish, ed., The Evolution of Language: Proceedings of the 10th international conference (EvoLang 10). It’s only £87.67 on Amazon, (but it may be wiser to email the authors if you don’t have a friend with a copy).