The mode of mastication of foods was examined through visual analysis with videofluorography, using agar and gelatin jellies as test foods. The mode altered from compression with the tongue and hard palate to shearing with the dentition as the hardness of jelly was increased. The thresh-olds of hardness requiring a shift of mastication mode from compression to shearing were 0.08 kg for the agar jelly and 0.03 kg for the gelatin jelly, although the gelatin jelly shear strain was larger. Rupture stress was also found to be an important factor in changing the mode. Visual analysis of videofluorography revealed that the food texture may be recognize by initial compression between the tongue and hard palate, around the incisive papilla. Very soft food was treated in the some way as liquid food. The mastication mode of a food may be determined according to the texture. The food was mastication either by compression with the tongue and hard palate or by shearing with the dentition. It was suspected that the process of initial compression of food with the tongue and the incisive papilla region is the first step of texture recognition.

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We defined changes in equivalent series resistance of neck electrical impedance at 50 kHz during swallowing as impedance pharyngography (IPG), and have proposed a new measurement and evaluation methods of swallowing. IPG was influenced by activities of related organs during swallowing, IPG waveforms accurately recorded the swallowing process. The 4 parameters for evaluation of swallowing were decided using swallowing sound. The parameters are as follows: (1) pharyngeal transit time; (2) ration of impedance change; (3) similarity ratio; (4) timing of swallowing sound. We compared these parameters between old subject group and young subject group and discussed change of parameters and swallowing function with aging. Considering results of discriminant analysis using 130 healthy subject's data, we showed possibility of discrimination of swallowing ability. We expect IPG to provide the following advantages over conventional diagnostic techniques: it is a quantitative method that allows for the objective assessment of swallowing function; it is a simple procedure that is convenient for the patient and could be used for screening; it is inexpensive and non-invasive, so could be performed repeatedly in situations such as rehabilitation; and it has highly portable equipment suitable for community use.

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The present study examined the relationship between rheological and swallowing characteristics of Liquid foods prepared by the addition of commercial thickening agents indispensable to meals for people with swallowing disorders.<SR>Rheological characteristics were studied for starch-based and guar-gum-based Liquid foods prepared, by the addition of thickening agents, to be of comparable hardness. For samples prepared to have yogurt-like hardness, the smaller the apparent viscosity (η app), or storage modulus (G'), the easier it was to swallow the sample. Videomanofluography was employed for examining bolus samples whose hardness was altered into three stages (equivalent to salad oil, mayonnaise and mashed potatoes, respectively) by the addition of thickening agents. Ultrasonic tomography was used on model boluses having mashed potato-like hardness, for studying the tongue movement at the time of swallowing.
These studies revealed how healthy people take food into their oral cavities, perceive the rheological/swallowing characteristics of the food, transform their tongues in order to create easy-to-swallow boluses, and control the driving force of their tongues so that the boluses can be passed onto the pharynx. The study results also implied that controlling the driving force of the tongue serves to keep constant the speed at which the bolus passes through the pharynx

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