Marieke Schouwstra

An evolutionary approach to sign language emergence: From state to process

Understanding the relationship between gesture, sign, and speech offers a valuable tool for investigating how language emerges from a nonlinguistic state. We propose that the focus on linguistic status is problematic, and a shift to focus on the processes that shape these systems serves to explain the relationship between them and contributes to the central question of how language evolves.

The perceptual effect of air sacs

This paper presents work on air sacs that extends the work presented by de Boer, (2008a). In that paper, and before (Fitch, 2000) air sacs were identified as a likely feature of our evolutionary ancestors that may have been lost because of the evolution of speech. In the mean time, a more accurate understanding of air sac acoustics has been achieved (de Boer, 2008b; Riede et al., 2008). Ape-like air sacs modify the acoustics of a vocal tract in three ways: they add a lowfrequency resonance (near the resonance frequency of the air sac itself), they shift up the resonances of the vocal tract without the air sac, and they shift these resonances closer together. The question that is addressed in the present paper is how these changes influence perception of the difference between vocalizations.

The origins of word order universals: Evidence from corpus statistics and silent gesture

Why are some patterns of noun phrase order (e.g., N-Adj-Num-Dem, ‘houses big five these’) much more common than others (e.g., N-Dem-Num-Adj, ‘houses these five big’)? An intriguing possibility is that this distribution emerges in response to a general cognitive bias favouring a transparent relationship between conceptual structure and linear order – an isomorphism bias. In conceptual structure, Adj is closest to N, then Num, then Dem (Fig. 1A). Linear orders that can be read off this nested structure are isomorphic, and these orders are the most common cross-linguistically. Previous experimental work has found an isomorphism in both traditional artificial language learning (Culbertson & Adger, 2014), and silent gesture experiments (Culbertson et al., 2016). For example, Culbertson et al. (2016) asked non-signing English speakers to communicate simple pictures using only gesture. Items were groups of 4 or 5 (Num) objects (N), either spotted or striped (Adj), in a proximal or distal location (Dem). Participants spontaneously improvised isomorphic gestures that did not reflect their native language. These results suggest that an isomorphism bias is present, however they leave open the origin of this bias. In particular, they cannot tell us the origins of the conceptual structure that word order is isomorphic to. Here we show that the conceptual structure of the noun phrase is learnable by observing simple statistics about objects in the world. Intuitively, our proposal is this: properties (~Adj) are more inherent to objects than numerosities (~Num), and location or discourse status (~Dem) is generally not an inherent feature of objects (cf. Rijkhoff 2002). More precisely, we quantify this notion using point-wise mutual information (Fig. 1B), a measure of the strength of association between pairs of elements. Using linguistic corpora as a proxy for the world, we can measure average pmi 212

Constituent Order in Improvised Gesture Reflects Speaker Perspective

The majority of languages with a dominant word order use either SOV or SVO (Dryer, 2013). The improvised gesture paradigm, in which participants use only gesture to convey information, is increasingly being used to investigate this asymmetry. In one of the earliest studies of this kind, Goldin-Meadow et al. (2008) claimed that Agent-Patient-Action, (here represented as APV but typically equated with SOV), reflects the ‘natural’ order of elements in improvised gesture. Other authors argue that APV is the natural order only for some types of event and that constituent order in improvised gesture reflects certain properties of an event, such as its temporal structure (Christensen et al., 2016) or the semantic relation between entities and actions (Schouwstra & Swart, 2014). Meir et al. (2017) suggest that gesture order is conditioned on saliency: human entities are more cognitively salient than inanimate entities and are therefore expressed first. Here we investigate the role of saliency in more detail. We present evidence that manipulating the visual saliency of the agent can influence the relative order of other constituents. Twenty-eight participants were shown pictures of scenes in which a human agent performed an action on an inanimate patient, for example, a man kicking a large potted plant (Fig. 1(a)). They were instructed to describe each scene using only improvised gesture and no speech. Participants were randomly assigned to one of two conditions: the ‘generic’ condition in which agents represented generic humans such as a man or a woman, or the ‘character’ condition where more visually salient agents were presented, such as a pirate or a punk. Patients were inanimate objects of a similar size to the agents and were depicted in a state of falling as a result of the action. We found that in the subset of trials where the agent, patient and action were expressed exactly once, the predominant order in the character condition was AVP; in the generic condition the majority order was APV (Fig. 1(b)). However, looking across all trials, we found that participants were significantly more likely to omit the agent in the generic condition (62% of trials) compared with the character condition (17%) (p<0.001). This suggests that participants in the 215

The cultural evolution of spatial modulations in artificial sign languages

Sign languages use a range of linguistic tools to denote the relationship between a predicate and its arguments, some which are shared with spoken languages (e.g. lexical contrasts and word order). However, many sign languages also make use of modality-specific spatial modulations to denote who does what to whom. The most common manifestation cross-linguistically of such spatial modulations is referential indexing, where animate arguments are indexed with a location in space and those indexed locations are referred to over a stretch of discourse to refer to the same argument. A characteristic example of this is given in 1); the man and the woman are represented by indexed locations—a and b, respectively—and the verb ask moves between the referenced locations.

I see what you did there: The role of iconicity in the acquisition of signs

Recent theoretical syntheses offer a view of language in which iconicity – a perceived resemblance between form and meaning – is seen as a fundamental design feature alongside arbitrariness (Dingemanse et. al. 2015). Under this view, iconicity serves to bootstrap acquisition, and there is a large body of work from both spoken and gestural modalities confirming that iconic signs are easier to acquire than arbitrary signs (for an overview, see Lockwood & Dingemanse, 2015; Perniss et. al. 2010). However, two recent studies suggest a more nuanced picture of iconicity’s contribution to learning: In an artificial language learning experiment using a whistled language, Verhoef et. al. (2016) found that whistles were reproduced less accurately in a condition where iconicity was possible compared to a condition where iconicity was disrupted by scrambling the correspondence between signals and meanings. Similarly, in a longitudinal study of phonological development in British Sign Language (BSL) learners, Ortega & Morgan (2015) found that learners produce iconic signs with less articulatory accuracy than arbitrary signs of equal complexity. These two results are apparently contradictory to the idea that iconicity provides a learning advantage, but we suggest this is because most iconicity learning studies have focused on the acquisition of the mapping between form and meaning, thus potentially obscuring subtleties relating to the acquisition of the form. We present the results of an experiment focusing on iconicity’s role in the acquisition of forms. In line with Ortega & Morgan (2015) and Verhoef et. al. (2016), we predict that while iconicity helps to acquire new mappings, it may also lead to less precise encoding of forms. We presented learners (n = 36, no previous experience of a signed language) with an artificial gestural language based on iconic and arbitrary signs from BSL. We measured performance on an immediate imitation task, using the 3D body-tracking capabilities of Microsoft Kinect to quantify the trajectories of learners’ wrists during production. This allows comparison of gestures produced by different participants using Dynamic 492

The critical period and preservation of emerged vowel systems

The critical period for language acquisition is often assumed to be nothing more than a by-product of development. However, evolutionary computer simulations show that it can be explained as a result of biological evolution (Hurford, 1991). In the present study the aim is not to explain how and why this age sensitivity evolved but to investigate the consequences of this individual-level disadvantage on a culturally evolving vowel system as a whole. Using two different agent-based computer models it will be argued that a difference in learning ability between children and adults can improve the stabilization and preservation of complexity of vowel systems in a changing population. The first model is a re-implementation of the one described by de Boer and Vogt (1999), which consists of a population of agents that interact through imitation games using realistic mechanisms for production and perception of vowels. The agents have a vowel memory in which they store learned prototypes of vowels and in response to their interactions with other agents they update their memory and learn new sounds. Analogous to the results of de Boer and Vogt (1999) the model shows that a population in which new members are born and old members die, a critical period stabilizes vowel systems over the generations. In this case the adults provide the learners with a stable target facilitating the acquisition process. Figure 1 shows the difference in the changes of the vowel system after transmission in a population with or without age structure. The second model is a variation on the first which integrates the linguistic paradigm of Optimality Theory (OT). In this version of the model, the agents imitate each other using their own bidirectional stochastic OT grammar (Boersma & Hamann, 2008) consisting of a ranked set of articulatory and cue constraints. To produce or perceive a speech signal, a set of possible candidate forms is evaluated by the grammar. The candidate that violates the fewest highly ranked constraints is selected. In response to their interactions with other agents they learn by adjusting (a) No age structure (b) Age structure Figure 1. Emerged vowel systems in the first model. Initial vowel system in grey. the ranking values in their grammar. This new approach replicates the results of the stabilizing effect on the emerged vowel systems. The results suggest that the critical period might be more than just an unfortunate consequence of development since its influence …