Most human languages are conveyed through the medium of sound, and thus understanding the way language sound works is central to understanding human language. This project addresses an unusual language sound phenomenon, initial consonant mutation: the initial consonant of a word varies to express grammatical information about that word, for example the possessives in Welsh, e.g. cath 'cat', fy nghath 'my cat', dy gath 'your cat', ei chath 'her cat'. In order to address big questions like "How do such systems evolve historically?", "How can children learn initial mutation?", and "Why does this not occur in a language like English?", it is important to first fully understand the properties of the mutating consonants for speakers of a language with initial consonant mutation. This is the research goal, with respect to Welsh, a language with a rich and productive system of initial consonant mutation. In addition, many Americans are of Welsh descent. The primary heritage language of this community is Welsh, a medium for a rich culture of literature, song, poetry, history, etc. It also provides an important window into the world-view and culture of the ancestors of the Welsh-American community. Sadly, the Welsh language is endangered. There are no monolingual speakers. In Wales, the number of speakers is now less than 20% of the population and there is a real danger that the language will decline below critical mass and no longer be viable. The potential loss to the understanding of the culture and background of so many Welsh and Welsh-Americans is tragic. The research to be conducted here will both help document extraordinary aspects of the grammatical system and provide resources for pedagogical materials essential in the revival of the language. The interdisciplinary and international team will apply a diversity of investigative tools: perceptual studies using masked priming, production studies using acoustic analysis and ultrasound for articulatory study, traditional field work involving elicitation, judgment tasks, statistical corpus work, and two acquisition studies (one with adults; one with children). These heterogeneous methodologies allow the team to approach the investigation of consonant mutation from a variety of directions, thus providing a uniquely comprehensive view of the phenomenon. The sub-projects are diverse, but focus on two central questions: i) whether mutations are best viewed as lexical or phonological phenomena; and ii) what the precise phonological properties of mutations are. These studies will also impact linguistic theory, including our understanding of lexical access in a language where a lot of morphological information is concentrated in the beginning of the word and in our understanding of the organization of phonological systems and alternations. The core of the team has done similar work on Scottish Gaelic and done logistical and descriptive advance work on Welsh, and so is uniquely positioned for this project. This award was made possible by the SBE-RCUK Lead Agency Agreement.