Sibilant differentiation before and after tongue cancer surgery: Acoustics, kinematics and the role of sensorimotor control

This study characterises articulatory-kinematic strategies to differentiate the sibilants /s/ and /ʃ/ in individuals before and after tongue cancer surgery. We further evaluate whether successful differentiation can be predicted by auditory and somatosensory motor learning abilities. Acoustic and electromagnetic articulography data were collected longitudinally (pre-surgery, and 6, 12, and 18 months post-surgery) from Dutch individuals treated for T1-T3 tongue tumours (n = 12). Sex- and age-matched typical speakers (n = 11) were tested once. We analysed the Euclidean distance (ED) between the tongue's position for /s/ and /ʃ/, alongside the centre of gravity. Altered formant feedback and bite-block experiments assessed motor learning from auditory and somatosensory input. Speakers showed a reduced ED between sibilants at the tongue tip (TT) six months post-surgery compared to pre-surgery. While performance improved over time, pre-surgery levels were not regained. ED reductions were associated with changes in lip aperture and jaw positioning. No differences were found between patients and typical speakers in acoustic or kinematic measures at any time point. No robust association was found between auditory/somatosensory motor learning ability and sibilant differentiation. Together, while TT control was reduced following tongue cancer surgery, speakers compensated using the lips and jaw to preserve the sibilant contrast.