This chapter presents an overview of what is currently known about phonetic and phonological first language (L1) attrition and drift in bilingual speech and introduces a new theory of bilingual speech, Attrition & Drift in Access, Production, and Perception Theory (ADAPPT). Attrition and drift are defined and differentiated along several dimensions, including duration of change, source in second language (L2) experience, consciousness, agency, and scope. We address why findings of attrition and drift are important for our overall understanding of bilingual speech and draw links between ADAPPT and well-known theories of L2 speech, such as the revised Speech Learning Model (SLM-r), the Perceptual Assimilation Model-L2 (PAM-L2), and the Second Language Linguistic Perception model (L2LP). The significance of findings revealing attrition and drift is discussed in relation to different linguistic subfields. The chapter raises the question of how attrition and drift potentially interact to influence speech production and perception in the bilingual’s L1 over the life span; additional directions for future research are pointed out as well.

Chapter 3 is devoted to the origin, initiation, and modeling of sound change. It begins withtheories of why sound change exists and discusses the teleological and nonteleological approaches. It then connects various models of sound change to these initiation stages. The most pressing question in these models is whether they build on the notion of accumulation of errors, or the involvement of social context such that social interpretation lies at the heart of change initiation. From the micro perspective, the chapter then discusses how change propagates in the individual speaker or listener and how sound change may lead to phonologization as its final stage. It contrasts Neogrammarian sound change with lexical diffusion. It further connects exemplar theories and sound change by extending exemplar knowledge to social meaning. The chapter then addresses the state of the art in /str/-retraction research. It spans the entire linguistic attention to /str/-retraction, from Labov’s early fieldnotes, to Shapiro and Lawrence’s theoretical accounts, to later phonetic and sociolinguistic approaches. Based on the theoretical backdrop provided before and the state of the art in /str/-centered linguistic research, the research hypotheses of the study are then introduced.

Chapter 2 explains the phonetic and phonological background of sibilant analysis.It first establishes a definition of the phoneme and then continues to describe the sounds involved based on an articulatory point of view. These are then connected to acoustic theories of speech production that illustrate how prototypical articulatory gestures create the resulting sound waves that are perceived as phonemes. It specifically explains how source filter theory and turbulence are important to the production of sibilants. It then illustrates how the acoustic output created can be quantified and classified based on characteristics such as spectral mean, skewness, and kurtosis of the speech signal.

The chapter then moves on to suprasegmental theories and fundamentals of /str/-retraction research. It explains how exemplar models of the mental lexicon are suitable to describe the sound change at hand. It then briefly illustrates the uniqueness of triple-consonant clusters in English. As important processes in this sound change, coarticulation and assimilation are then differentiated.

When speech sounds are produced, articulatory movements for one sound overlap with those of the surrounding sounds, generating articulatory and acoustic signals that at any point in time are informative about two or more sounds, not just one. This process of intermingling of information about several speech sounds in the articulatory and acoustic signals is called coarticulation. This chapter synthesises theories and experimental findings of the last century on the nature of coarticulation, and shows how our modern understanding of this complex process is deeply rooted in theories that have evolved over decades due to novel experimental findings as well as critique from competing theories. After discussion of our current understanding of coarticulation, some suggestions for initiating students into the surprising effects of coarticulation are introduced.

Chapter 7 reviews the major theories of sound change that have emerged over the past centuries, honing in on more modern user-based theories most synergistic with sociophonetics.The chapter examines how sociophonetics, and its growth from work in sociolinguistics, has redirected the focus on sound change from a historical and system internal perspective to one forged by and crucially interconnected with the social needs of its users.Along these lines, the discussion emphasizes the empirical approach to the "problems" of sound change articulated in the foundational work by Weinreich, Herzog and Labov in 1968.Turning to recent research that explores these "problems" from a sociophonetic perspective, the treatment suggests that sociophonetics does not just continue a tradition of interest in sound change, it provides new opportunity to understand at a more fine-grained level than ever before the mechanisms underlying language change.