Evolving artificial sign languages in the lab: From improvised gesture to systematic sign

Why do languages tolerate heterography? An experimental investigation into the emergence of informative orthography

It is widely acknowledged that opaque orthographies place additional demands on learning, often requiring many years to fully acquire. It is less widely recognized, however, that such opacity may offer certain benefits in the context of reading. For example, heterographic homophones such as ⟨knight⟩ and ⟨night⟩ (words that sound the same but which are spelled differently) impose additional costs in learning but reduce ambiguity in reading. Here, we consider the possibility that-left to evolve freely-writing systems will sometimes choose to forego some simplicity for the sake of informativeness when there is functional pressure to do so. We investigate this hypothesis by simulating the evolution of orthography as it is transmitted from one generation to the next, both with and without a communicative pressure for ambiguity avoidance. In addition, we consider two mechanisms by which informative heterography might be selected for: differentiation, in which new spellings are created to differentiate meaning (e.g., ⟨lite⟩ vs. ⟨light⟩), and conservation, in which heterography arises as a byproduct of sound change (e.g., ⟨meat⟩ vs. ⟨meet⟩). Under pressure from learning alone, orthographic systems become transparent, but when combined with communicative pressure, they tend to favor some additional informativeness. Nevertheless, our findings also suggest that, in the long term, simpler, transparent spellings may be preferred in the absence of top-down explicit teaching.

Brain responses to a lab-evolved artificial language with space-time metaphors

What is the connection between the cultural evolution of a language and the rapid processing response to that language in the brains of individual learners? In an iterated communication study that was conducted previously, participants were asked to communicate temporal concepts such as "tomorrow," "day after," "year," and "past" using vertical movements recorded on a touch screen. Over time, participants developed simple artificial 'languages' that used space metaphorically to communicate in nuanced ways about time. Some conventions appeared rapidly and universally (e.g., using larger vertical movements to convey greater temporal durations). Other conventions required extensive social interaction and exhibited idiosyncratic variation (e.g., using vertical location to convey past or future). Here we investigate whether the brain's response during acquisition of such a language reflects the process by which the language's conventions originally evolved. We recorded participants' EEG as they learned one of these artificial space-time languages. Overall, the brain response to this artificial communication system was language-like, with, for instance, violations to the system's conventions eliciting an N400-like component. Over the course of learning, participants' brain responses developed in ways that paralleled the process by which the language had originally evolved, with early neural sensitivity to violations of a rapidly-evolving universal convention, and slowly developing neural sensitivity to an idiosyncratic convention that required slow social negotiation to emerge. This study opens up exciting avenues of future work to disentangle how neural biases influence learning and transmission in the emergence of structure in language.

Visual Form and Event Semantics Predict Transitivity in Silent Gestures: Evidence for Compositionality

Silent gesture is not considered to be linguistic, on par with spoken and sign languages. It is claimed that silent gestures, unlike language, represent events holistically, without compositional structure. However, recent research has demonstrated that gesturers use consistent strategies when representing objects and events, and that there are behavioral and clinically relevant limits on what form a gesture may take to effect a particular meaning. This systematicity challenges a holistic interpretation of silent gesture, which predicts that there should be no stable form-meaning correspondence across event representations. Here, we demonstrate to the contrary that untrained gesturers systematically manipulate the form of their gestures when representing events with and without a theme (e.g., Someone popped the balloon vs. Someone walked), that is, transitive and intransitive events. We elicited silent gestures and annotated them for manual features active in coding transitivity distinctions in sign languages. We trained linear support vector machines to make item-by-item transitivity predictions based on these features. Prediction accuracy was good across the entire dataset, thus demonstrating that systematicity in silent gesture can be explained with recourse to subunits. We argue that handshape features are constructs co-opted from cognitive systems subserving manual action production and comprehension for communicative purposes, which may integrate into the linguistic system of emerging sign languages. We further suggest that nonsigners tend to map event participants to each hand, a strategy found across genetically and geographically distinct sign languages, suggesting the strategy's cognitive foundation.

Self-Repair Increases Referential Coordination

When interlocutors repeatedly describe referents to each other, they rapidly converge on referring expressions which become increasingly systematized and abstract as the interaction progresses. Previous experimental research suggests that interactive repair mechanisms in dialogue underpin convergence. However, this research has so far only focused on the role of other-initiated repair and has not examined whether self-initiated repair might also play a role. To investigate this question, we report the results from a computer-mediated maze task experiment. In this task, participants communicate with each other via an experimental chat tool, which selectively transforms participants' private turn-revisions into public self-repairs that are made visible to the other participant. For example, if a participant, A, types "On the top square," and then before sending, A revises the turn to "On the top row," the server automatically detects the revision and transforms the private turn-revisions into a public self-repair, for example, "On the top square umm I meant row." Participants who received these transformed turns used more abstract and systematized referring expressions, but performed worse at the task. We argue that this is due to the artificial self-repairs causing participants to put more effort into diagnosing and resolving the referential coordination problems they face in the task, yielding better grounded spatial semantics and consequently increased use of abstract referring expressions.

How could we make a social robot? A virtual bargaining approach

What is required to allow an artificial agent to engage in rich, human-like interactions with people? I argue that this will require capturing the process by which humans continually create and renegotiate 'bargains' with each other. These hidden negotiations will concern topics including who should do what in a particular interaction, which actions are allowed and which are forbidden, and the momentary conventions governing communication, including language. Such bargains are far too numerous, and social interactions too rapid, for negotiation to be conducted explicitly. Moreover, the very process of communication presupposes innumerable momentary agreements concerning the meaning of communicative signals, thus raising the threat of circularity. Thus, the improvised 'social contracts' that govern our interactions must be implicit. I draw on the recent theory of virtual bargaining, according to which social partners mentally simulate a process of negotiation, to outline how these implicit agreements can be made, and note that this viewpoint raises substantial theoretical and computational challenges. Nonetheless, I suggest that these challenges must be met if we are ever to create AI systems that can work collaboratively alongside people, rather than serving primarily as valuable special-purpose computational tools. This article is part of a discussion meeting issue 'Cognitive artificial intelligence'.

Gaps in the Lexicon Restrict Communication

Across languages, words carve up the world of experience in different ways. For example, English lacks an equivalent to the Chinese superordinate noun tiáowèipǐn, which is loosely translated as "ingredients used to season food while cooking." Do such differences matter? A conventional label may offer a uniquely effective way of communicating. On the other hand, lexical gaps may be easily bridged by the compositional power of language. After all, most of the ideas we want to express do not map onto simple lexical forms. We conducted a referential Director/Matcher communication task with adult speakers of Chinese and English. Directors provided a clue that Matchers used to select words from a word grid. The three target words corresponded to a superordinate term (e.g., beverages) in either Chinese or English but not both. We found that Matchers were more accurate at choosing the target words when their language lexicalized the target category. This advantage was driven entirely by the Directors' use/non-use of the intended superordinate term. The presence of a conventional superordinate had no measurable effect on speakers' within- or between-category similarity ratings. These results show that the ability to rely on a conventional term is surprisingly important despite the flexibility languages offer to communicate about non-lexicalized categories.

Documenting a Reduction in Signing Space in Nicaraguan Sign Language Using Depth and Motion Capture

In this paper, we use motion tracking technology to document the birth of a brand new language: Nicaraguan Sign Language. Languages are dynamic entities that undergo change and growth through use, transmission, and learning, but the earliest stages of this process are generally difficult to observe as most languages have been used and passed down for many generations. Here, we observe a rare case of language emergence: the earliest stages of the new sign language in Nicaragua. By comparing the signing of the oldest and youngest signers of Nicaraguan Sign Language, we can track how the language itself is changing. Using motion tracking technology, we document a decrease in the size of articulatory space of Nicaraguan Sign Language signers over time. The reduction in articulatory space in Nicaraguan Sign appears to be the joint product of several decades of use and repeated transmission of this new language.

Testing the effects of congruence in adult multilingual acquisition with implications for creole genesis

Linguists from across sub-disciplines have noted that congruence (i.e., form-function mapping) across languages in contact seems to affect acquisition and play a role in language emergence (e.g. Creole genesis). However, because congruence is often confounded with other variables (e.g., frequency, language type, speakers' proficiency levels, perceptual salience, semantic transparency), it remains unclear whether congruence per se benefits learners. In this paper, we provide an experimental test of the effects of congruence on acquisition through an artificial language-learning experiment involving English (L1) and two artificial languages (Flugerdu and Zamperese). English-speakers who identified as "native" (i.e., first-language) speakers (N = 163) were randomly assigned to one of four conditions, varying which of the three languages expressed negation with congruent forms: all three languages; only Flugerdu and Zamperese; only English and Flugerdu; or none. Our findings show that participants better acquired the negation morpheme when the form was congruent with negation in English but not when the two artificial languages alone shared a congruent form. We likewise found unanticipated spillover effects in which participants better acquired the vocabulary and grammar of the artificial languages when all three languages had congruent negation forms. These findings provide insight into the effects of congruence on language acquisition in multilingual environments and Creole language formation.

Cognitive pragmatics: Insights from homesign conversations

Homesign is a visual-gestural form of communication that emerges between deaf individuals and their hearing interlocutors in the absence of a conventional sign language. I argue here that homesign conversations form a perfect testcase to study the extent to which pragmatic competence is foundational rather than derived from our linguistic abilities.

The Effects of Iconicity and Conventionalization on Word Order Preferences

Of the six possible orderings of the three main constituents of language (subject, verb, and object), two-SOV and SVO-are predominant cross-linguistically. Previous research using the silent gesture paradigm in which hearing participants produce or respond to gestures without speech has shown that different factors such as reversibility, salience, and animacy can affect the preferences for different orders. Here, we test whether participants' preferences for orders that are conditioned on the semantics of the event change depending on (i) the iconicity of individual gestural elements and (ii) the prior knowledge of a conventional lexicon. Our findings demonstrate the same preference for semantically conditioned word order found in previous studies, specifically that SOV and SVO are preferred differentially for different types of events. We do not find that iconicity of individual gestures affects participants' ordering preferences; however, we do find that learning a lexicon leads to a stronger preference for SVO-like orders overall. Finally, we compare our findings from English speakers, using an SVO-dominant language, with data from speakers of an SOV-dominant language, Turkish. We find that, while learning a lexicon leads to an increase in SVO preference for both sets of participants, this effect is mediated by language background and event type, suggesting that an interplay of factors together determines preferences for different ordering patterns. Taken together, our results support a view of word order as a gradient phenomenon responding to multiple biases.

Compositionality in Different Modalities: A View from Usage-Based Linguistics

The field of linguistics concerns itself with understanding the human capacity for language. Compositionality is a key notion in this research tradition. Compositionality refers to the notion that the meaning of a complex linguistic unit is a function of the meanings of its constituent parts. However, the question as to whether compositionality is a defining feature of human language is a matter of debate: usage-based and constructionist approaches emphasize the pervasive role of idiomaticity in language, and argue that strict compositionality is the exception rather than the rule. We review the major discussion points on compositionality from a usage-based point of view, taking both spoken and signed languages into account. In addition, we discuss theories that aim at accounting for the emergence of compositional language through processes of cultural transmission as well as the debate of whether animal communication systems exhibit compositionality. We argue for a view that emphasizes the analyzability of complex linguistic units, providing a template for accounting for the multimodal nature of human language.

Visual bodily signals as core devices for coordinating minds in interaction

The view put forward here is that visual bodily signals play a core role in human communication and the coordination of minds. Critically, this role goes far beyond referential and propositional meaning. The human communication system that we consider to be the explanandum in the evolution of language thus is not spoken language. It is, instead, a deeply multimodal, multilayered, multifunctional system that developed-and survived-owing to the extraordinary flexibility and adaptability that it endows us with. Beyond their undisputed iconic power, visual bodily signals (manual and head gestures, facial expressions, gaze, torso movements) fundamentally contribute to key pragmatic processes in modern human communication. This contribution becomes particularly evident with a focus that includes non-iconic manual signals, non-manual signals and signal combinations. Such a focus also needs to consider meaning encoded not just via iconic mappings, since kinematic modulations and interaction-bound meaning are additional properties equipping the body with striking pragmatic capacities. Some of these capacities, or its precursors, may have already been present in the last common ancestor we share with the great apes and may qualify as early versions of the components constituting the hypothesized interaction engine. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

Simultaneity as an Emergent Property of Efficient Communication in Language: A Comparison of Silent Gesture and Sign Language

Sign languages use multiple articulators and iconicity in the visual modality which allow linguistic units to be organized not only linearly but also simultaneously. Recent research has shown that users of an established sign language such as LIS (Italian Sign Language) use simultaneous and iconic constructions as a modality‐specific resource to achieve communicative efficiency when they are required to encode informationally rich events. However, it remains to be explored whether the use of such simultaneous and iconic constructions recruited for communicative efficiency can be employed even without a linguistic system (i.e., in silent gesture) or whether they are specific to linguistic patterning (i.e., in LIS). In the present study, we conducted the same experiment as in Slonimska et al. (2020) with 23 Italian speakers using silent gesture and compared the results of the two studies. The findings showed that while simultaneity was afforded by the visual modality to some extent, its use in silent gesture was nevertheless less frequent and qualitatively different than when used within a linguistic system. Thus, the use of simultaneous and iconic constructions for communicative efficiency constitutes an emergent property of sign languages. The present study highlights the importance of studying modality‐specific resources and their use for linguistic expression in order to promote a more thorough understanding of the language faculty and its modality‐specific adaptive capabilities.

The Seeds of the Noun–Verb Distinction in the Manual Modality: Improvisation and Interaction in the Emergence of Grammatical Categories

The noun–verb distinction has long been considered a fundamental property of human language, and has been found in some form even in the earliest stages of language emergence, including homesign and the early generations of emerging sign languages. We present two experimental studies that use silent gesture to investigate how noun–verb distinctions develop in the manual modality through two key processes: (i) improvising using novel signals by individuals, and (ii) using those signals in the interaction between communicators. We operationalise communicative interaction in two ways: a setting in which members of the dyad were in separate booths and were given a comprehension test after each stimulus vs. a more naturalistic face-to-face conversation without comprehension checks. There were few differences between the two conditions, highlighting the robustness of the paradigm. Our findings from both experiments reflect patterns found in naturally emerging sign languages. Some formal distinctions arise in the earliest stages of improvisation and do not require interaction to develop. However, the full range of formal distinctions between nouns and verbs found in naturally emerging language did not appear with either improvisation or interaction, suggesting that transmitting the language to a new generation of learners might be necessary for these properties to emerge.

How Language Learning and Language Use Create Linguistic Structure

Languages persist through a cycle of learning and use: You learn a language through immersion in the language used in your linguistic community, and in using language to communicate, you produce further linguistic data, which other people might learn from in turn. Languages change over historical time as a result of errors and innovations in these processes of learning and use; this article reviews experimental and computational methods that have been developed to test the hypothesis that those same processes of learning and use are responsible for creating the fundamental structural properties shared by all human languages, including some of the design features that make language such a powerful tool for communication.

Gesture is the primary modality for language creation

How language began is one of the oldest questions in science, but theories remain speculative due to a lack of direct evidence. Here, we report two experiments that generate empirical evidence to inform gesture-first and vocal-first theories of language origin; in each, we tested modern humans' ability to communicate a range of meanings (995 distinct words) using either gesture or non-linguistic vocalization. Experiment 1 is a cross-cultural study, with signal Producers sampled from Australia (n = 30, M_age = 32.63, s.d. = 12.42) and Vanuatu (n = 30, M_age = 32.40, s.d. = 11.76). Experiment 2 is a cross-experiential study in which Producers were either sighted (n = 10, M_age = 39.60, s.d. = 11.18) or severely vision-impaired (n = 10, M_age = 39.40, s.d. = 10.37). A group of undergraduate student Interpreters guessed the meaning of the signals created by the Producers (n = 140). Communication success was substantially higher in the gesture modality than the vocal modality (twice as high overall; 61.17% versus 29.04% success). This was true within cultures, across cultures and even for the signals produced by severely vision-impaired participants. The success of gesture is attributed in part to its greater universality (i.e. similarity in form across different Producers). Our results support the hypothesis that gesture is the primary modality for language creation.

Visual form of ASL verb signs predicts non-signer judgment of transitivity

Longstanding cross-linguistic work on event representations in spoken languages have argued for a robust mapping between an event’s underlying representation and its syntactic encoding, such that–for example–the agent of an event is most frequently mapped to subject position. In the same vein, sign languages have long been claimed to construct signs that visually represent their meaning, i.e., signs that are iconic. Experimental research on linguistic parameters such as plurality and aspect has recently shown some of them to be visually universal in sign, i.e. recognized by non-signers as well as signers, and have identified specific visual cues that achieve this mapping. However, little is known about what makes action representations in sign language iconic, or whether and how the mapping of underlying event representations to syntactic encoding is visually apparent in the form of a verb sign. To this end, we asked what visual cues non-signers may use in evaluating transitivity (i.e., the number of entities involved in an action). To do this, we correlated non-signer judgments about transitivity of verb signs from American Sign Language (ASL) with phonological characteristics of these signs. We found that non-signers did not accurately guess the transitivity of the signs, but that non-signer transitivity judgments can nevertheless be predicted from the signs’ visual characteristics. Further, non-signers cue in on just those features that code event representations across sign languages, despite interpreting them differently. This suggests the existence of visual biases that underlie detection of linguistic categories, such as transitivity, which may uncouple from underlying conceptual representations over time in mature sign languages due to lexicalization processes.

Imperfect language learning reduces morphological overspecification: Experimental evidence

It is often claimed that languages with more non-native speakers tend to become morphologically simpler, presumably because non-native speakers learn the language imperfectly. A growing number of studies support this claim, but there is a dearth of experiments that evaluate it and the suggested explanatory mechanisms. We performed a large-scale experiment which directly tested whether imperfect language learning simplifies linguistic structure and whether this effect is amplified by iterated learning. Members of 45 transmission chains, each consisting of 10 one-person generations, learned artificial mini-languages and transmitted them to the next generation. Manipulating the learning time showed that when transmission chains contained generations of imperfect learners, the decrease in morphological complexity was more pronounced than when the chains did not contain imperfect learners. The decrease was partial (complexity did not get fully eliminated) and gradual (caused by the accumulation of small simplifying changes). Simplification primarily affected double agent-marking, which is more redundant, arguably more difficult to learn and less salient than other features. The results were not affected by the number of the imperfect-learner generations in the transmission chains. Thus, we provide strong experimental evidence in support of the hypothesis that iterated imperfect learning leads to language simplification.

Emergence or Grammaticalization? The Case of Negation in Kata Kolok

Typological comparisons have revealed that signers can use manual elements and/or a non-manual marker to express standard negation, but little is known about how such systematic marking emerges from its gestural counterparts as a new sign language arises. We analyzed 1.73 h of spontaneous language data, featuring six deaf native signers from generations III-V of the sign language isolate Kata Kolok (Bali). These data show that Kata Kolok cannot be classified as a manual dominant or non-manual dominant sign language since both the manual negative sign and a side-to-side headshake are used extensively. Moreover, the intergenerational comparisons indicate a considerable increase in the use of headshake spreading for generation V which is unlikely to have resulted from contact with Indonesian Sign Language varieties. We also attest a specialized negative existential marker, namely, tongue protrusion, which does not appear in co-speech gesture in the surrounding community. We conclude that Kata Kolok is uniquely placed in the typological landscape of sign language negation, and that grammaticalization theory is essential to a deeper understanding of the emergence of grammatical structure from gesture.

Expression unleashed: The evolutionary and cognitive foundations of human communication

Human expression is open-ended, versatile, and diverse, ranging from ordinary language use to painting, from exaggerated displays of affection to micro-movements that aid coordination. Here we present and defend the claim that this expressive diversity is united by an interrelated suite of cognitive capacities, the evolved functions of which are the expression and recognition of informative intentions. We describe how evolutionary dynamics normally leash communication to narrow domains of statistical mutual benefit, and how expression is unleashed in humans. The relevant cognitive capacities are cognitive adaptations to living in a partner choice social ecology; and they are, correspondingly, part of the ordinarily developing human cognitive phenotype, emerging early and reliably in ontogeny. In other words, we identify distinctive features of our species' social ecology to explain how and why humans, and only humans, evolved the cognitive capacities that, in turn, lead to massive diversity and open-endedness in means and modes of expression. Language use is but one of these modes of expression, albeit one of manifestly high importance. We make cross-species comparisons, describe how the relevant cognitive capacities can evolve in a gradual manner, and survey how unleashed expression facilitates not only language use, but also novel behaviour in many other domains too, focusing on the examples of joint action, teaching, punishment, and art, all of which are ubiquitous in human societies but relatively rare in other species. Much of this diversity derives from graded aspects of human expression, which can be used to satisfy informative intentions in creative and new ways. We aim to help reorient cognitive pragmatics, as a phenomenon that is not a supplement to linguistic communication and on the periphery of language science, but rather the foundation of the many of the most distinctive features of human behaviour, society, and culture.

Amount of Learning and Signal Stability Modulate Emergence of Structure and Iconicity in Novel Signaling Systems

Iterated language learning experiments that explore the emergence of linguistic structure in the laboratory vary considerably in methodological implementation, limiting the generalizability of findings. Most studies also restrict themselves to exploring the emergence of combinatorial and compositional structure in isolation. Here, we use a novel signal space comprising binary auditory and visual sequences and manipulate the amount of learning and temporal stability of these signals. Participants had to learn signals for meanings differing in size, shape, and brightness; their productions in the test phase were transmitted to the next participant. Across transmission chains of 10 generations each, Experiment 1 varied how much learning of auditory signals took place, and Experiment 2 varied temporal stability of visual signals. We found that combinatorial structure emerged only for auditory signals, and iconicity emerged when the amount of learning was reduced, as an opportunity for rote‐memorization hampers the exploration of the iconic affordances of the signal space. In addition, compositionality followed an inverted u‐shaped trajectory raising across several generations before declining again toward the end of the transmission chains. This suggests that detection of systematic form‐meaning linkages requires stable combinatorial units that can guide learners toward the structural properties of signals, but these combinatorial units had not yet emerged in these unfamiliar systems. Our findings underscore the importance of systematically manipulating training conditions and signal characteristics in iterated language learning experiments to study the interactions between the emergence of iconicity, combinatorial and compositional structure in novel signaling systems.

A Systematic Investigation of Gesture Kinematics in Evolving Manual Languages in the Lab

Silent gestures consist of complex multi‐articulatory movements but are now primarily studied through categorical coding of the referential gesture content. The relation of categorical linguistic content with continuous kinematics is therefore poorly understood. Here, we reanalyzed the video data from a gestural evolution experiment (Motamedi, Schouwstra, Smith, Culbertson, & Kirby, 2019), which showed increases in the systematicity of gesture content over time. We applied computer vision techniques to quantify the kinematics of the original data. Our kinematic analyses demonstrated that gestures become more efficient and less complex in their kinematics over generations of learners. We further detect the systematicity of gesture form on the level of thegesture kinematic interrelations, which directly scales with the systematicity obtained on semantic coding of the gestures. Thus, from continuous kinematics alone, we can tap into linguistic aspects that were previously only approachable through categorical coding of meaning. Finally, going beyond issues of systematicity, we show how unique gesture kinematic dialects emerged over generations as isolated chains of participants gradually diverged over iterations from other chains. We, thereby, conclude that gestures can come to embody the linguistic system at the level of interrelationships between communicative tokens, which should calibrate our theories about form and linguistic content.

Pantomimic fossils in modern human communication

Bodily mimesis, the capacity to use the body representationally, was one of the key innovations that allowed early humans to go beyond the 'baseline' of generalized ape communication and cognition. We argue that the original human-specific communication afforded by bodily mimesis was based on signs that involve three entities: an expression that represents an object (i.e. communicated content) for an interpreter. We further propose that the core component of this communication, pantomime, was able to transmit referential information that was not limited to select semantic domains or the 'here-and-now', by means of motivated-most importantly iconic-signs. Pressures for expressivity and economy then led to conventionalization of signs and a growth of linguistic characteristics: semiotic systematicity and combinatorial expression. Despite these developments, both naturalistic and experimental data suggest that the system of pantomime did not disappear and is actively used by modern humans. Its contemporary manifestations, or pantomimic fossils, emerge when language cannot be used, for instance when people do not share a common language, or in situations where the use of (spoken) language is difficult, impossible or forbidden. Under such circumstances, people bootstrap communication by means of pantomime and, when these circumstances persist, newly emergent pantomimic communication becomes increasingly language-like. This article is part of the theme issue 'Reconstructing prehistoric languages'.

Disentangling Pantomime From Early Sign in a New Sign Language: Window Into Language Evolution Research

In this study, we aim to disentangle pantomime from early signs in a newly-born sign language: Sao Tome and Principe Sign Language. Our results show that within 2 years of their first contact with one another, a community of 100 participants interacting everyday was able to build a shared language. The growth of linguistic systematicity, which included a decrease in use of pantomime, reduction of the amplitude of signs and an increase in articulation economy, showcases a learning, and social interaction process that constitutes a continuum and not a cut-off system. The human cognitive system is endowed with mechanisms for symbolization that allow the process of arbitrariness to unfold and the expansion of linguistic complexity. Our study helps to clarify the role of pantomime in a new sign language and how this role might be linked with language itself, showing implications for language evolution research.

Constructing a protolanguage: reconstructing prehistoric languages in a usage-based construction grammar framework

Construction grammar is an approach to language that posits that units and structures in language can be exhaustively described as pairings between form and meaning. These pairings are called constructions and can have different degrees of abstraction, i.e. they span the entire range from very concrete (armadillo, avocado) to very abstract constructions such as the ditransitive construction (I gave her a book). This approach has been applied to a wide variety of different areas of research in linguistics, such as how new constructions emerge and change historically. It has also been applied to investigate the evolutionary emergence of modern fully fledged language, i.e. the question of how systems of constructions can arise out of prelinguistic communication. In this paper, we review the contribution of usage-based construction grammar approaches to language change and language evolution to the questions of (i) the structure and nature of prehistoric languages and (ii) how constructions in prehistoric languages emerged out of non-linguistic or protolinguistic communication. In particular, we discuss the possibilities of using constructions as the main unit of analysis both in reconstructing predecessors of existing languages (protolanguages) and in formulating theories of how a potential predecessor of human language in general (protolanguage) must have looked like. This article is part of the theme issue 'Reconstructing prehistoric languages'.

Simplicity and informativeness in semantic category systems

Recent research has shown that semantic category systems, such as color and kinship terms, find an optimal balance between simplicity and informativeness. We argue that this situation arises through pressure for simplicity from learning and pressure for informativeness from communicative interaction, two distinct pressures that often (but not always) pull in opposite directions. Another account argues that learning might also act as a pressure for informativeness, that learners might be biased toward inferring informative systems. This results in two competing hypotheses about the human inductive bias. We formalize these competing hypotheses in a Bayesian iterated learning model in order to simulate what kinds of languages are expected to emerge under each. We then test this model experimentally to investigate whether learners' biases, isolated from any communicative task, are better characterized as favoring simplicity or informativeness. We find strong evidence to support the simplicity account. Furthermore, we show how the application of a simplicity principle in learning can give the impression of a bias for informativeness, even when no such bias is present. Our findings suggest that semantic categories are learned through domain-general principles, negating the need to posit a domain-specific mechanism.

Lexical Iconicity is differentially favored under transmission in a new sign language: The effect of type of iconicity

Observations that iconicity diminishes over time in sign languages pose a puzzle--why should something so evidently useful and functional decrease? Using an archival dataset of signs elicited over 15 years from 4 first-cohort and 4 third-cohort signers of an emerging sign language (Nicaraguan Sign Language), we investigated changes in pantomimic (body-to-body) and perceptual (body-to-object) iconicity. We make three key observations: (1) there is greater variability in the signs produced by the first cohort compared to the third; (2) while both types of iconicity are evident, pantomimic iconicity is more prevalent than perceptual iconicity for both groups; and (3) across cohorts, pantomimic elements are dropped to a greater proportion than perceptual elements. The higher rate of pantomimic iconicity in the first-cohort lexicon reflects the usefulness of body-as-body mapping in language creation. Yet, its greater vulnerability to change over transmission suggests that it is less favored by children's language acquisition processes.