Language emergence can take multiple paths: Using motion capture to track axis use in Nicaraguan Sign Language
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Research on emerging 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 et al. 2010). This has been suggested to reflect a transition from iconicity rooted in the body (Meir et al. 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.