Physical models of the vocal tract with a flapping tongue for flap and liquid sounds

Certain sounds are difficult for children to produce, even if the sounds are in their native language. For example, Japanese /r/ can be difficult for Japanese children to learn. Second language learners can also have difficulty acquiring certain sounds. For example, Japanese speakers learning English often have difficulty with English /r/ and /l/. To address this problem, we have developed two new physical models of the vocal tract: one for flap sounds (Model A) and another for liquid sounds (Model B). Each of them has a flapping tongue, and for Model B, the length of the tongue is variable. When the tongue is short, we can produce alveolar/retroflex approximants, and when the tongue is long we can produce lateral approximants. We recorded several sets of sounds produced by these models, analyzed the speech data, and used them for perceptual experiments. From the acoustic analysis and the perceptual experiments, we confirmed that the sounds produced by Model A were heard as Japanese /r/, and the sounds produced by Model B were heard as English /r/ and /l/. Furthermore, the models are helpful for practicing pronunciation because learners can see the tongue, alter tongue position manually, and hear the output sounds.