What does method validation look like for forensic voice comparison by a human expert?

Method validation has gained traction within forensic speech science. The community recognises the need to demonstrate that the analysis methods used are valid, but finding a way to do so has been more straightforward for some analysis methods than for others. This article addresses the issue of method validation for the Auditory Phonetic and Acoustic (AuPhA) approach to forensic voice comparison. Although it is possible to take inspiration from general regulatory guidance on method validation, it is clear that these cannot be transposed on to all forensic analysis methods with the same degree of success. Particularly with respect to an analysis method like AuPhA, and in a field of the size and characteristics of forensic speech science, a bespoke approach to method validation is required. In this article we address the discussions that have been taking place around method validation, and illustrate one possible solution to demonstrating the validity of voice comparison by a human expert using the AuPhA method. In doing so we consider the constraints placed on sole practitioners, which generally go unacknowledged.

Editors' Introduction and Review: Sociolinguistic Variation and Cognitive Science.

Sociolinguists study the interaction between language and society. Variationist sociolinguistics - the subfield of sociolinguistics which is the focus of this issue - uses empirical and quantitative methods to study the production and perception of linguistic variation. Linguistic variation refers to how speakers choose between linguistic forms that say the same thing in different ways, with the variants differing in their social meaning. For example, how frequently someone says fishin' or fishing depends on a number of factors, such as the speaker's regional and social background and the formality of the speech event. Likewise, if listeners are asked to use a rating scale make judgements about speakers who say fishin' or fishing, their ratings depend on what other social characteristics are attributed to the speaker. This issue aims to reflect the growing number of interactions that bring variationist sociolinguistics into contact of different branches of cognitive science. After presenting current trends in sociolinguistics, we identify five areas of contact between the two fields: cognitive sociolinguistics, sociolinguistic cognition, acquisition of variation, computational modeling, and a comparative approach of variation in animal communication. We then explain the benefits of interdisciplinary work: fostering the study of variability and cultural diversity in cognition; bringing together data and modeling; understanding the cognitive mechanisms through which sociolinguistic variation is processed; examining indexical meaning; exploring links between different levels of grammar; and improving methods of data collection and analysis. Finally we explain how the articles in this issue contribute to each of these benefits. We conclude by suggesting that sociolinguistics holds a strategic position for facing the challenge of building theories of language through integrating its linguistic, cognitive, and social aspects at the collective and individual levels.

Missed Connections at the Junction of Sociolinguistics and Speech Processing.

In recent years, significant momentum has built up in efforts to integrate the social with the cognitive in theoretical models of speech production/processing and phonological representation. While acknowledging these advances, we argue that what limits our ability to elaborate models of processing and representation in which social-indexical properties of speech are effectively integrated is that we remain some way from fully understanding how these properties are manifested within spoken interaction in the first place. We explore some of these limitations, drawing on data from a study of sociophonetic variability in a population of speakers of Australian English. We discuss issues relating to methods for capturing variability in the realization of vowels and consonants, and we highlight the pivotal role of speech style and the challenges that this raises for models of production and processing.

Changing Words and Sounds: The Roles of Different Cognitive Units in Sound Change.

This study considers the role of different cognitive units in sound change: phonemes, contextual variants and words. We examine /u/-fronting and /j/-dropping in data from three generations of Derby English speakers. We analyze dynamic formant data and auditory judgments, using mixed effects regression methods, including generalized additive mixed models (GAMMs). /u/-fronting is reaching its end-point, showing complex conditioning by context and a frequency effect that weakens over time. /j/-dropping is declining, with low-frequency words showing more innovative variants with /j/ than high-frequency words. The two processes interact: words with variable /j/-dropping (new) exhibit more fronting than words that never have /j/ (noodle) even when the /j/ is deleted. These results support models of change that rely on phonetically detailed representations for both word- and sound-level cognitive units.