As many as 20 million Americans identify themselves as Scottish or Scots/Irish in descent. One of the primary heritage languages of this community, Scottish Gaelic is the medium for a rich culture of literature, song, poetry, history and indigenous knowledge-systems. It also provides an important window into the world-view and culture of the ancestors of the Scottish-American community. The loss of native speaker knowledge about this endangered language is imminent. The Scottish Gaelic language is of particular interest to scientific linguists. Gaelic is very different from English in the ways it signals grammatical relationships between words. In particular it has a mechanism for indicating grammatical notions such as tense, gender, aspect, and possession by changing the first consonant of one of the words in the relationship. For example, the initial consonant in the word c� 'dog' (a k sound) is pronounced with a hard ch sound like German Bach when it is appears after possessive words like mo 'my' (written as mo ch�). These changes, called "initial consonant mutations," are a productive and critical part of the grammatical system of the language. This mechanism for indicating grammatical inflection is extremely rare in the world's languages and is very poorly understood. In order for linguists to properly understand the sound system of a language, they have to use instrumental measures of how speakers articulate sounds and use psycholinguistic experiments to measure how speakers understand and use the patterns of sounds. Using modern linguistic instrumental and psycholinguistic techniques. Professors Andrew Carnie, Diana Archangeli, Michael Hammond, Natasha Warner and Adam Ussishkin, along with Scottish Gaelic native speaker Muriel Fisher will investigate the articulation, patterning, and perception of initial consonant mutations. For example, this study will determine whether speakers store both the mutated and non-mutated words in their minds by asking them to identify the word while they listen to obscured (or "masked") speech sounds. A related experiment, where the sounds people hear are subtly artificially modified (or "gated"), will be used to study that the exact point in the sound stream at which listeners can identify whether the word is mutated or non-mutated. A study of the relative statistical frequency of sounds in mutated and non-mutated in a collection of language (or corpus) will show how productive the process is and how it corresponds to statistics on the frequency of sounds in the larger grammatical system of the language. Psycholinguistic techniques, including judgments and nonsense word tasks will be used to investigate the mental procedures speakers use to produce these mutations. Finally the actual articulation of these mutations will be investigated using modern phonetic instrumental measures such as ultrasound and airflow volume. The output of this research project will be a description of the Gaelic consonant mutation that will help complete an on-going description of the language. In addition, in doing this research graduate students will be trained in the techniques of sound analysis of an endangered language. This training will allow the students to conduct similar experimental studies on other endangered languages. This work has significant implications for documenting and preserving the linguistic traditions of the Scottish and Scottish-American communities.