Tissue vibrations in the larynx produce most sounds that comprise vocal communication in mammals. Larynx morphology is thus predicted to be a key target for selection, particularly in species with highly developed vocal communication systems. Here, we present a novel database of digitally modeled scanned larynges from 55 different mammalian species, representing a wide range of body sizes in the primate and carnivoran orders. Using phylogenetic comparative methods, we demonstrate that the primate larynx has evolved more rapidly than the carnivoran larynx, resulting in a pattern of larger size and increased deviation from expected allometry with body size. These results imply fundamental differences between primates and carnivorans in the balance of selective forces that constrain larynx size and highlight an evolutionary flexibility in primates that may help explain why we have developed complex and diverse uses of the vocal organ for communication.

Recent work suggests that not all aspects of learning benefit from an iconicity advantage (Ortega, 2017). We present the results of an artificial sign language learning experiment testing the hypothesis that iconicity may help learners to learn mappings between forms and meanings, whilst having a negative impact on learning specific features of the form. We used a 3D camera (Microsoft Kinect) to capture participants’ gestures and quantify the accuracy with which they reproduce the target gestures in two conditions. In the iconic condition, participants were shown an artificial sign language consisting of congruent gesture–meaning pairs. In the arbitrary condition, the language consisted of non-congruent gesture–meaning pairs. We quantified the accuracy of participants’ gestures using dynamic time warping (Celebi et. al., 2013). Our results show that participants in the iconic condition learn mappings more successfully than participants in the arbitrary condition, but there is no difference in the accuracy with which participants reproduce the forms. While our work confirms that iconicity helps to establish form–meaning mappings, our study did not give conclusive evidence about the effect of iconicity on production; we suggest that iconicity may only have an impact on learning forms when these are complex.

Research on emergent sign languages suggests that younger sign languages may make greater use of the z-axis, moving outwards from the body, than more established sign languages when describing the relationships between participants and events (Padden, Meir, Aronoff, and Sandler, 2010). This has been suggested to reflect a transition from iconicity rooted in the body (Meir, Padden, Aronoff, and Sandler, 2007) towards a more abstract schematic iconicity. We present the results of an experimental investigation into the use of axis by signers of Nicaraguan Sign Language (NSL). We analysed 1074 verb tokens elicited from NSL signers who entered the signing community at different points in time between 1974 and 2003. We used depth and motion tracking technology to quantify the position of signers’ wrists over time, allowing us to build an automated and continuous measure of axis use. We also consider axis use from two perspectives: a camera-centric perspective and a signer-centric perspective. In contrast to earlier work, we do not observe a trend towards increasing use of the x-axis. Instead we find that signers appear to have an overall preference for the z-axis. However, this preference is only observed from the camera-centric perspective. When measured relative to the body, signers appear to be making approximately equal use of both axes, suggesting the preference for the z-axis is largely driven by signers moving their bodies (and not just their hands) along the z-axis. We argue from this finding that language emergence patterns are not necessarily universal and that use of the x-axis may not be a prerequisite for the establishment of a spatial grammar.

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.

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