Fig. 3

Primary tongue actions mimicked during food oral processing. Coronal plane US images (i) along with their corresponding image-based 3D reconstructions (ii–iv) of the artificial tongue for each dominant motion. Initial isometric views (ii) aid in visualising tongue movements, followed by coronal (iii) and, if necessary, sagittal views (iv) to elucidate the shape of the artificial tongue. White arrows and X symbol denote the inflation/deflation or no-actioned states of tongue air chambers. Dashed lines, highlighted in red (US images) and green (3D reconstructions), qualitatively illustrate the mimicked shape. In the simulated oral environment, tongue mobility is constrained. In the initial phase of VL oral processing (a), the tongue transports the liquid from the frontal to the mid part of the oral cavity by slightly elevating the tip and depressing the tongue body (i). The artificial tongue replicates this action with a depression-like shape (ii–iii), maintaining the frontal air chamber with no action while the lateral chambers deflate. For both ASS and SS, oral processing begins with the tongue compressing the food against the hard palate (b.i). The artificial tongue mimics this action with a dome-like shape (ii), maintaining the frontal air chamber with no action while symmetrically inflating both lateral chambers (iii–iv). During mixing (c.i), the tongue moves the food product within the oral cavity to facilitate its mixing with saliva. The artificial tongue replicates this action with an asymmetrical dome-like shape (ii), alternating inflation and deflation in both lateral chambers (iii–iv). During shearing, evident tongue and hard palate contact produce a complex shear state (d.i). The artificial tongue mimics this with an asymmetrical dome-like shape (ii–iv), like the shape used for mixing, but with the tongue contacting against the hard palate to produce shear. At the end of oral processing, just before swallowing, food boli are collected in the back of the tongue (e.i). The artificial tongue mimics this action by inflating the frontal air chamber to squeeze slightly the food bolus while deflating both lateral chambers (ii–iii), producing a depression-like shape to contain the ready-to-swallow food bolus.