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.

Evidence that listeners attend to and track subphonemic phonetic details is indicated by listeners’ ability to reliably connect subphonemic variation and, often, socio-indexical associations in ways that align with the patterns realized in production. Bilinguals are presented with the task not only of associating within-language variation (e.g., social group X is connected to a particular range of phonetic realizations within language Y) but also of attending to how ethnolects and bilingually accented speech index social categories across languages. Having access to multiple languages also gives bilingual speakers a larger repertoire with which to index language- and community-specific social meaning. This chapter outlines the linguistic structures bilinguals may connect across their languages and then presents a specific exemplar model, noting the opportunities within the model’s structure for bilingual dynamics. The heterogeneity of bilingual individuals and speech communities is necessarily addressed, as this dynamic adds to the complexity and intrigue of studying bilingual populations.

Centuries of contact between Older Scots and the Scandinavian language of Norn, coupled with geographic isolation, has resulted in the highly distinctive dialects spoken in the Orkney and Shetland Isles today. In this chapter, we document the socio-historical context which led to the formation of these dialects, and look to a range of studies which describe these dialects’ lexical, phonological and morphosyntactic forms. We note forms shared with other varieties of Scots but concentrate mostly on the highly localised features not found in mainland Scotland. In addition to broad comparisons between Orkney and Shetland, we also document the dialect diversity within each location. Finally, we turn to bidialectalism, and specifically how speakers may have access to two ‘codes’ in their linguistic repertoire, where Standard Scottish English is used alongside localised vernaculars, and how this might impact on dialect attrition in the coming years.