Variation in the FACE vowel across West Yorkshire: Implications for forensic speaker comparisons

In the field of sociophonetics, research is largely focused on the documentation of regional variability. However, the majority of literature in the United Kingdom often reports on variation at a macro-level (e.g. Northern, Yorkshire, West Yorkshire) rather than at a more local level (e.g. West Yorkshire: Bradford, Calderdale, Kirklees, Leeds, Wakefield). Traditionally, for sociophoneticians, examining regional variation at a broader level is adequate for answering research questions related to language change or more general variation. For practical applications (e.g. forensic, speech technology), however, more fine-grained regional analysis is necessary. This paper analyses over 2000 FACE tokens from three metropolitan boroughs (Bradford, Kirklees and Wakefield) within West Yorkshire, in order to determine the extent to which F1~F3 vary across the region. Results suggest that for FACE, these three boroughs within West Yorkshire are more regionally stratified than previously acknowledged. These findings are of particular importance to the forensic speech science community, as experts rely on these regional nuances in order to make important judgments related to strength of the speech evidence in a case. Should decisions be made without the greater understanding of local-level variation, the strength of evidence risks being over- or under-estimated.