The LexIKHuM project [1] aims at developing a human-machine communication system based on a kinesthetic lexicon inspired by natural human gestural communication: co-speech gestures [CSG] and sign languages [SL]. As we would like to enable the AI machine to communicate its degree of certainty with regard to the message delivered, we studied the kinesthetic properties of epistemic gestures. Previous studies have identified some markers of the epistemic gesture, such as rapid head nods to express certainty (in German and Turkish SL; in French, English and Catalan CSG [2 3 4 5]) or slow head tilts to express uncertainty. However, these studies have only looked at the epistemic gesture as a whole and are focused on SL or CSG. In the LexIKHuM project, we analyze the sub-parametric properties of these gestures, searching for common features in SL and CSG. We assume that (a) some properties of the movement carried in the 3 degrees of freedom [DoF] of the head are involved in the construction of epistemic gestures in SL and CSG (such as the amplitude of the flexion/extension movement or the duration of the abduction/adduction movement of the neck); and (b) that the direction of gaze associated with the head movements is also relevant to express epistemicity. To investigate these hypotheses, we examined head movements and gaze positions in epistemic gestures in DEGELS [6], a parallel corpus of French CSG and French SL (LSF). We followed a protocol inspired by the prosodic analysis of SL and kinesiological studies [7 8]. We manually (a) identified the epistemic sequences of that corpus (with inter-annotator agreement) using ELAN; (b) transcribed head and gaze movements using the Typannot transcription system [9] on a sample of 40 epistemic sequences; and semi-automatically (c) generated the measures of the head movements in the different DoFs with AlphaPose software (see an example in Figure 1). Our preliminary studies reveal that (a) gestures formed in a context of certainty show a greater amplitude of movement of the flexion/extension of the head in SL and CSG; (b) in a context of uncertainty, we observe more holding of the flexion/extension movement and greater amplitude of neck rotation movements in LSF. We then combined our observations of neck movements with gaze direction in epistemic contexts. Our preliminary observations show that speakers of French and LSF tend to displace their gaze from their head position when expressing uncertainty: we plan to confirm these initial findings using automatic gaze detection software, such as OpenFace. In the near future, LexIKHuM will apply the same protocol presented here to identify more sub-parametric features conveying epistemicity on other articulators (such as shoulders and torso). We will also explore other meanings that will be implemented in our kinesthetic lexicon, such as the expression of urgency or danger. Figure 1. Visualization of neck flexion and extension measurements - identification of certainty markers Keywords: gesture; SL; epistemicity; human-machine communication; head movement; gaze References [1] Projet « Lexique d’Interaction Kinesthésique Humain Machine [LexIKHuM] » (2021 2025). https://anr.fr/Projet-ANR-20-CE33-0012 [2] Debras C. (2017). The shrug: forms and meanings of a compound enactment. Gesture, 16(1): 1-34. [3] Herrmann A. (2013). Modal and focus particles in Sign Languages: a cross-linguistics study. De Gruyter Mouton (Berlin/Boston). [4] Karabüklü S., Bross F., Wilbur R., Hole D. (2018). Modal signs and scope relations in TİD. Proc. “Formal and Experimental Advances in Sign language Theory [FEAST]”, 2: 82-92. [5] Roseano P., González M., Borràs-Comes J., Prieto P. (2016). Communicating epistemic stance: how speech and gesture patterns reflect epistemicity and evidentiality. Discourse Processes, 53: 135-174. [6] Braffort A., Boutora L. (2012). DEGELS1: a comparable corpus of French Sign Language and co speech gestures. Proc. “8th Intl. Conf. on Language Resources and Evaluation [LREC 2012]”. [7] Boutet D. (2018). Pour une approche kinésiologique de la gestualité. HDR, Université de Rouen. [8] Puupponen A., Wainio T., Burger B., Jantunen T. (2015). Head movements in Finnish Sign Language on the basis of motion capture data: a study of the form and function of nods, nodding, head thrusts, and head pulls. Sign Language & Linguistics, 18: 41-89.