Headshakes in NGT: Relation between phonetic properties & linguistic functions

Non-manual markers (such as facial expressions and head movements) have been shown to fulfil a wide range of grammatical functions across sign languages (Pfau and Quer, 2010). One nonmanual marker that is very wide-spread is headshake used to express negation (Oomen and Pfau, 2017). While negation and headshake have been studied for a variety of sign languages, phonetic/kinematic research on headshake has been mostly absent. In this paper, we conduct a phonetic analysis of headshake in Sign Language of the Netherlands using a Computer Vision solution, namely OpenFace (Baltrusaitis et al., 2018). We specifically analyze whether linguistic properties of headshake (e.g. spreading and the type of signs co-occurring with the headshake) influence its phonetic form.