Hyoid and tongue surface movements in speaking and eating.

The human hyoid moves continuously in feeding, facilitating movements of the tongue surface and the processing and transport of food. The hypothesis that similar hyoid movements support tongue movements in speech was tested in 10 normal young adults of both sexes, who were recorded with lateral-projection videofluorography when feeding on hard and soft foods and when reading the 'Grandfather Passage', which includes the major vowel-consonant combinations in English. Recordings were made with and without tongue-markers. Images were analysed with a digital frame grabber and computer. Each participant served as his/her own control. The hyoid moved continuously during speech and feeding. In speech, hyoid motions were irregular and not linked to jaw movement, as they were for feeding. The centroids and variances of the domains for all reference points were compared for speech and feeding; the centroid represents the average position of a structure and variance its amount of motion. Gape and hyoid centroids were significantly different for feeding and speech (P<0.001), but differences for gape averaged <1mm while the difference for the hyoid centroid was >7mm. There were no significant differences in gape attributable to sex. Consistent with the known differences in hyolaryngeal position there were significant sex differences in hyoid centroid (P=0.031) but not variance. In speech, tongue-markers had a smaller spatial domain (P=0.001) condensed within the larger feeding domain. The small shift in the gape centroid does not explain the larger forward shift of the hyoid during speech. These findings raise questions about the neuromotor control of hyoid position in the two behaviours and the biomechanics of the supralaryngeal vocal tract.