Fig. 4. Schematic representation for the calculation of tongue curvature. The solid line, including seven discrete points, represents a digitised section of the tongue. A circle with radius r and centre M is stepwise estimated along the tongue through each set of three contiguous points along the tongue axis, e.g. the three black dots s_n–1, s_n and s_n+1 [i.e. for s=(0, 0.02, 0.04,..., 1); equations 1, 2, 3]. Subsequently, at s_n, the curvature C (i.e. 1/r) was determined. This was repeated for each point at the tongue axis except for the tongue base (s=0) and tongue tip (s=1).