This dissertation investigates the relationship between linguistic factors and speaker-dependent information in speech sounds, with a particular focus on the Dutch language and on fricative and... Show moreThis dissertation investigates the relationship between linguistic factors and speaker-dependent information in speech sounds, with a particular focus on the Dutch language and on fricative and nasal consonants. Using spontaneous telephone speech corpora, this work provides an empirical contribution to forensic speech science by aiming to answer the question of whether acoustic-phonetic features from consonants should be extracted from and compared across different linguistic environments, also considering the recording condition.This thesis reports the results of a number of studies on the sources of variation in consonant acoustics. First, it analyses the role of phonetic context and syllabic position for speaker variation that is present in fricative and nasal consonants, which have previously been shown to be useful sounds in forensic speaker comparisons. Second, the interactions between linguistic effects and recording conditions (telephone versus microphone) are investigated. Finally, forensic strength-of-evidence was derived using Bayesian likelihood-ratio modelling to determine the practical consequences of these findings to forensic speaker comparisons. Show less
In Moroccan Dutch, /s/ has been claimed to be pronounced as retracted [s] (towards /ʃ/) in certain consonant clusters. Recently, retracted s-pronunciation has also been attested in endogenous Dutch... Show moreIn Moroccan Dutch, /s/ has been claimed to be pronounced as retracted [s] (towards /ʃ/) in certain consonant clusters. Recently, retracted s-pronunciation has also been attested in endogenous Dutch. We tested empirically whether Moroccan Dutch [s] is indeed more retracted than endogenous Dutch [s] in relevant clusters. Additionally, we tested whether the inter-speaker variation of /s/ is smaller between Moroccan Dutch speakers than between endogenous Dutch speakers, as expected if retraction of /s/ would be used as identity marker in in-group conversations in Moroccan Dutch. The [s] realizations of 21 young, male Moroccan Dutch and 21 endogenous Dutch speakers were analyzed. Analyses of the spectral centre of gravity (CoG) show that both groups of speakers had more retracted pronunciations of [s] in typically retracting contexts than in typically non-retracting contexts. However, Moroccan Dutch speakers had higher CoG in both contexts than endogenous Dutch speakers, refuting the stronger retraction expected in Moroccan Dutch speakers. The inter-speaker variation was larger between Moroccan Dutch speakers than between endogenous-Dutch speakers, refuting the expected usage of /s/ retraction as a group identity marker. Show less
In forensic speech science, nasals are often reported to be particularly useful in characterizing speakers because of their low within-speaker and high between-speaker variability. However,... Show moreIn forensic speech science, nasals are often reported to be particularly useful in characterizing speakers because of their low within-speaker and high between-speaker variability. However, empirical acoustic data from nasal consonants indicate that there is a somewhat larger role for the oral cavity on nasal consonant acoustics than is generally predicted by acoustic models. For example, in read speech, nasal consonant acoustics show lingual coarticulation that differs by nasal consonant, and syllabic position also seems to affect realizations of nasal consonants within speakers. In the current exploratory study, the within and between-speaker variation in the most frequent nasals in Standard Dutch, /n/ and /m/, was investigated. Using 3,695 [n] and 3,291 [m] tokens sampled from 54 speakers’ spontaneous telephone utterances, linear mixed-effects modelling of acoustic-phonetic features showed effects of phonetic context that differed by nasal consonant and by syllabic position. A following speaker-classification test using multinomial logistic regression on the acoustic-phonetic features seems to indicate that nasals displaying larger effects of phonetic context also perform slightly better in speaker classification, although differences were minor. This might be caused by between-speaker variation in the degree and timing of lingual coarticulatory gestures. Show less
Previous studies have suggested that female voices may impede verbal processing. For example, words were remembered less well and lexical decision was slower when spoken by a female speaker. The... Show morePrevious studies have suggested that female voices may impede verbal processing. For example, words were remembered less well and lexical decision was slower when spoken by a female speaker. The current study tried to replicate this gender effect in an auditory semantic/associative priming task that excluded any effects of speaker variability and extended previous research by examining the role of two voice features important in perceived gender: pitch and formant frequencies. Additionally, listener gender was included in the experimental design. Results show that, contrary to previous findings, there is no evidence that a lexical decision of a target word is slower when spoken by a female speaker than by a male speaker for female and male listeners. Additionally, the semantic/associative priming effect was not affected by speaker gender, neither did female mean pitch or formants predict the semantic/associative priming effect. At the behavioural level, the current study found no evidence for a gender effect in a semantic/associative priming task. Show less
Although previous work has shown that some speech sounds are more speaker-specific than others, not much is known about the speaker information of the same segment in different linguistic contexts.... Show moreAlthough previous work has shown that some speech sounds are more speaker-specific than others, not much is known about the speaker information of the same segment in different linguistic contexts. The present study, there- fore, investigated whether Dutch fricatives /s/ and /x/ from telephone dialogues contain differential speaker informa- tion as a function of syllabic position and labial co-articulation. These linguistic effects, established in earlier work on read broadband speech, were first investigated. Using a corpus of Dutch telephone speech, results showed that the telephone bandwidth captures the expected effects of perseverative and anticipatory labialization for dorsal fricative /x/, for which spectral peaks fall within the telephone band, but not for coronal fricative /s/, for which the spectral peak falls outside the telephone band. Multinomial logistic regression shows that /s/ contains slightly more speaker information than /x/ in telephone speech and that speaker information is distributed across the speech signal in a sys- tematic way; even though differences in classification accuracy were small, codas and tokens with labial neighbors yielded higher scores than onsets and tokens with non-labial neighbors for both /s/ and /x/. These findings indicate that speaker information in the same speech sound is not the same across linguistic contexts. Show less