Design and preliminary evaluation of the vocal cords and articulator of an infant-like vocal robot "Lingua"

Several observational studies have suggested that the vocal development of an infant towards language acquisition is by interaction with caregivers. However, owing to the difficulty of controlling infant vocalization, the underlying mechanisms of the process and how they are affected by the behavior of the caregiver are yet to be clearly established. Towards clarifying these outstanding issues, we developed an infant-like vocal robot, "Lingua," as a controllable vocal platform that affords a model of real infant vocalization. Lingua has two features, namely, infant-like voice and high articulation capability. The shapes of its vocal cords and vocal tract are similar to those of a 6-month-old infant as determined from anatomical data. Seven degrees of freedom of tongue articulation were realized by a sophisticated design comprising linkage mechanisms inside a miniaturized vocal tract, and this enabled the achievement of high articulation performance. The relationship between the material hardness of the vocal fold and its acoustic performance was examined, and the results of preliminary experiments showed that the robot could vocalize almost the same ranges of fundamental frequencies and vowel-like utterances as an infant.