**5. Conclusions**

We investigated how participants distinguish between typical (verb-like) and atypical (noun-like) targets in novel manual communication systems across two experiments that examined the effect of communication on the emergence of the noun–verb distinction. We found that, across both experiments, clear distinctions emerged in the earliest improvisation stages. All of the participants placed gestures serving a verb role at the end of their utterances, and placed gestures serving a noun role earlier in the utterance. Participants also were biased to produce a base hand on gestures serving a verb function. The strategies used to distinguish between typical and atypical targets emerged early during improvisation, suggesting that the distinction between nouns and verbs is a basic feature of how we communicate, becoming conventionalised in languages over time. Although interacting participants converged on a shared communication system, we did not see further changes, indicating that other processes (such as the transmission of the system to new learners) are involved in the conventionalisation of noun–verb distinctions. We sugges<sup>t</sup> that using experimental methods to test these hypotheses alongside data from natural languages can help to build a robust picture of how systematic grammatical distinctions emerge.

**Supplementary Materials:** Files including the annotations made from video data (used for analysis) and all analysis scripts can be found at: https://osf.io/qzgjt (accessed on 21 March 2022). Video data from experiment 1 is available at: https://datashare.ed.ac.uk/handle/10283/3195 (accessed on 21 March 2022).

**Author Contributions:** Conceptualization, Y.M., K.M., N.A., M.F., S.K. and S.G.-M.; Formal analysis, Y.M., K.M., N.A., M.F., S.K. and S.G.-M.; Funding acquisition, S.K. and S.G.-M.; Investigation, Y.M. and K.M.; Methodology, Y.M., K.M., S.K. and S.G.-M.; Validation, K.M., N.A. and M.F.; Visualization, Y.M.; Writing—original draft, Y.M.; Writing—review & editing, Y.M., K.M., N.A., M.F., S.K. and S.G.-M. All authors have read and agreed to the published version of the manuscript.

**Funding:** Funding for experiment 1 was awarded to YM as a Carnegie Caledonian Doctoral Scholarship from the Carnegie Trust for the Universities of Scotland (award number PHD060261). Funding for experiment 2 was provided by a gran<sup>t</sup> from NSF BCS-1654154 to SGM, SK is a co-PI.

**Institutional Review Board Statement:** Ethical approval for study 1 was granted by the ethical review board in the Department of Linguistics and English Language at the University of Edinburgh. Ethical approval for study 2 was granted by the Institutional Review Board at the University of Chicago (IRB Study 97-074).

**Informed Consent Statement:** Informed consent was obtained from all participants prior to the start of the study.

**Data Availability Statement:** Video data from experiment 1, data files used for analysis and analysis scripts are publicly available (see Supplementary Materials).

**Acknowledgments:** We would also like to thank Kenny Smith, Marieke Schouwstra and Jennifer Culbertson for their contributions to the design of Experiment 1, and Destiny Gale, Nicola Lustig, Gayathri Rao and Gowri Rao, who coded the data for both experiments.

**Conflicts of Interest:** The authors declare no conflict of interest.
