Palatolingual contact stress (pressure) and pattern are indispensable parameters in investigation of the dynamic properties of human tongue motion during palatal consonant phonation. Palatolingual contact can be detected by dynamic palatometry, a practical technique using electrodes imbedded in a thin palatal plate that adheres to the hard palate. Dynamic palatometry using the electrical impedance of palatolingual contact detects binary palatolingual contact patterns, but it is not capable of measuring palatolingual contact pressure.
In this paper, we first present a new type of cantilevered force-sensor mounted on a palatal plate for high-sensitivity, high-accuracy measurement of palatolingual contact pressure and tongue force. The system consists of three components: a cantilevered force-sensor mounted on a palatal plate, a multi-channel amplifier to supplement the strain gauge, and a computer for data acquisition and signal processing. The cantilevered force sensor, which consists of a strain gauge and a cantilever, is mounted on a palatal plate attached to the hard palate. The force sensor is 3.0 mm wide, 5.5 mm long, and 1.1 mm thick. Its measurement error is less than 2.8%. When a load of 5 gf applied to the protuberance of the force sensor is instantaneously removed, the time required for reducing the output level from 90% to 10% is 0.3 ms. The palatal plate is a thin plastic plate shaped in such a way that it attaches tightly to the subject’s hard palate. Multiple force sensors can be mounted at arbitrary positions on the palatal plate, and the palatolingual contact pressure and tongue force can be determined using such multiple sensors.
Second, we propose an algorithm for estimating tongue force based on palatolingual contact pressure. The palatal regions are divided into triangular elements with vertices located at the three-dimensional positions of the force sensors, using the Delaunay triangulation method. Palatolingual contact pressure at arbitrary positions within the triangular elements of the hard palate is estimated using linear interpolation, based on measured values and positions of the force sensors. Tongue force can be calculated via surface integration over the distribution of palatolingual pressure values in the palatal region. To verify the sensor’s function, we simultaneously measured the weight of a tongue-like elastic test body using an electronic scale and our force-sensor palatal plate. The results indicated that the accuracy of tongue force measurements using the force-sensor palatal plate is 4.7%.
The palatolingual contact pressures and patterns of five adult male subjects who had no history of speech disorder were measured during Japanese /CV/ (C=/t, d, n, s/ and V=/a, i, u, e, o/) phonation. The proposed system allows direct observation of the dynamic aspects of palatolingual contact pressure and tongue force during the phonation of consonants.
