Perception of English /i/ and /I/ by Japanese and Spanish Listeners: Longitudinal Results

Flege’s Speech Learning Model predicts that if an L2 learner perceives an L2 speech sound as similar to an L1 speech sound, the two sounds will be combined as a diaphone category, the properties of which will eventually be intermediate between the properties of the L1 and L2 sound. In contrast if the L2 sound is perceived as new, then a new category will be established with properties which may eventually match the properties of the L2 sound. Canadian English has two high front vowels: tense /i/ and lax /I/ differing in spectral and duration properties. Japanese has two high front vowels: long /i:/ and short /i/ differing in duration only. English /i/ and /I/ are expected to be perceived as similar to Japanese /i:/ and /i/, and Japanese learners of English are predicted to establish diaphone categories. Their identification of English /i/ and /I/ is predicted to initially match their perception of Japanese /i:/ and /i/, but eventually be intermediate between the native norms for the L1 and L2 categories. Spanish has one high front vowel. Spanish learners of English are predicted to perceive English /I/ as less similar to Spanish /i/ than English /i/, and are predicted to eventually establish a new /i:/ category. Their identification of English /i/ and /I/ is predicted to initially be poor but eventually match that of English listeners. These predictions were tested using a multidimensional edited-speech continuum covering the English words /bIt bit bId bid/. Properties which varied in the continuum included vowel spectral properties and vowel duration. A longitudinal study was conducted testing Japanese and Spanish speaking learners of English one month and six months after their arrival in Canada. Japanese listeners were found to have a primarily duration-based categorical boundary between English /i/ and /I/ which did not change between the initial and final tests. Spanish listeners did not have a categorical identification pattern in the initial test, but they did establish duration-based or spectrally-based categorical boundaries by the time of the final test. Results were therefore consistent with the theoretical predictions

An acoustic and statistical analysis of Spanish mid-vowel allophones

In 1918 Navarro Tomás claimed that Spanish mid vowels have open and close allophones. Whilst some acoustic studies have supported these claims, others have not. The conclusions in these studies were subjective since they failed to apply statistical analysis to the acoustic data. Statistical analysis is required to determine whether data with a range of values can be grouped into distinct categories. The present study investigates the production of Spanish /e/ and /o/ in several contexts in which Navarro Tomás claimed open and close allophones would be found. Recordings were made of a male and a female speaker of educated Madrid Spanish, the dialect which Navarro Tomás originally described. First and second formants were measured and statistically analysed. Formant frequencies did not cluster into two groups associated with the contexts in which Navarro Tomás claimed each allophone would occur. Other potential allophones were identified: fronted and retracted allophones for /o/; and close-fronted, central, and openretracted allophones for /e/.In 1918 Navarro Tomás claimed that Spanish mid vowels have open and close allophones. Whilst some acoustic studies have supported these claims, others have not. The conclusions in these studies were subjective since they failed to apply statistical analysis to the acoustic data. Statistical analysis is required to determine whether data with a range of values can be grouped into distinct categories. The present study investigates the production of Spanish /e/ and /o/ in several contexts in which Navarro Tomás claimed open and close allophones would be found. Recordings were made of a male and a female speaker of educated Madrid Spanish, the dialect which Navarro Tomás originally described. First and second formants were measured and statistically analysed. Formant frequencies did not cluster into two groups associated with the contexts in which Navarro Tomás claimed each allophone would occur. Other potential allophones were identified: fronted and retracted allophones for /o/; and close-fronted, central, and openretracted allophones for /e/.En 1918 Navarro Tomás afirmó que había alófonos abiertos y cerrados de las vocales medias de castellano. Aunque los resultados de varios estudios subsiguientes están de acuerdo con la afirmación, otros están en desacuerdo. Las conclusiones de estos estudios son subjetivas porque no analizaron estadísticamente los datos acústicos. Un análisis estadístico es imprescindible para determinar si se pueden asignar datos con una variedad de valores a categorías distintas. El presente estudio investiga la producción de /e/ y /o/ castellano en varios de los contextos en que Navarro Tomás afirmó que había alófonos abiertos y cerrados. Se grabaron las producciones de un hombre y una mujer, hablantes de un dialecto madrileño educado, el dialecto que Navarro Tomás describió. Se medió y analizó estadísticamente el primer y el segundo formante de las vocales. Las frecuencias de los formantes no se apiñaron en dos grupos asociados con los contextos en que Navarro Tomás afirmó aparecía cada alófono. Se identificaron otros alófonos potenciales: anterior y posterior para /o/; y anterior-cerrado, central, y posterior-abierto para /e/

What should a forensic practitioner's likelihood ratio be? II

In the debate as to whether forensic practitioners should assess and report the precision of the strength of evidence statements that they report to the courts, I remain unconvinced by proponents of the position that only a subjectivist concept of probability is legitimate. I consider this position counterproductive for the goal of having forensic practitioners implement, and courts not only accept but demand, logically correct and scientifically valid evaluation of forensic evidence. In considering what would be the best approach for evaluating strength of evidence, I suggest that the desiderata be (1) to maximise empirically demonstrable performance; (2) to maximise objectivity in the sense of maximising transparency and replicability, and minimising the potential for cognitive bias; and (3) to constrain and make overt the forensic practitioner’s subjective-judgement based decisions so that the appropriateness of those decisions can be debated before the judge in an admissibility hearing and/or before the trier of fact at trial. All approaches require the forensic practitioner to use subjective judgement, but constraining subjective judgement to decisions relating to selection of hypotheses, properties to measure, training and test data to use, and statistical modelling procedures to use – decisions which are remote from the output stage of the analysis – will substantially reduce the potential for cognitive bias. Adopting procedures based on relevant data, quantitative measurements, and statistical models, and directly reporting the output of the statistical models will also maximise transparency and replicability. A procedure which calculates a Bayes factor on the basis of relevant sample data and reference priors is no less objective than a frequentist calculation of a likelihood ratio on the same data. In general, a Bayes factor calculated using uninformative or reference priors will be closer to a value of 1 than a frequentist best estimate likelihood ratio. The bound closest to 1 based on a frequentist best estimate likelihood ratio and an assessment of its precision will also, by definition, be closer to a value of 1 than the frequentist best estimate likelihood ratio. From a practical perspective, both procedures shrink the strength of evidence value towards the neutral value of 1. A single-value Bayes factor or likelihood ratio may be easier for the courts to handle than a distribution. I therefore propose as a potential practical solution, the use of procedures which account for imprecision by shrinking the calculated Bayes factor or likelihood ratio towards 1, the choice of the particular procedure being based on empirical demonstration of performance

The impact in forensic voice comparison of lack of calibration and of mismatched conditions between the known-speaker recording and the relevant-population sample recordings

In a 2017 New South Wales case, a forensic practitioner conducted a forensic voice comparison using a Gaussian mixture model – universal background model (GMM-UBM). The practitioner did not report the results of empirical tests of the performance of this system under conditions reflecting those of the case under investigation. The practitioner trained the model for the numerator of the likelihood ratio using the known-speaker recording, but trained the model for the denominator of the likelihood ratio (the UBM) using high-quality audio recordings, not recordings which reflected the conditions of the known-speaker recording. There was therefore a difference in the mismatch between the numerator model and the questioned-speaker recording versus the mismatch between the denominator model and the questioned-speaker recording. In addition, the practitioner did not calibrate the output of the system. The present paper empirically tests the performance of a replication of the practitioner’s system. It also tests a system in which the UBM was trained on known-speaker-condition data and which was empirically calibrated. The performance of the former system was very poor, and the performance of the latter was substantially better

A response to: "NIST experts urge caution in use of courtroom evidence presentation method"

A press release from the National Institute of Standards and Technology (NIST)could potentially impede progress toward improving the analysis of forensic evidence and the presentation of forensic analysis results in courts in the United States and around the world. "NIST experts urge caution in use of courtroom evidence presentation method" was released on October 12, 2017, and was picked up by the phys.org news service. It argues that, except in exceptional cases, the results of forensic analyses should not be reported as "likelihood ratios". The press release, and the journal article by NIST researchers Steven P. Lund & Harri Iyer on which it is based, identifies some legitimate points of concern, but makes a strawman argument and reaches an unjustified conclusion that throws the baby out with the bathwater

Admissibility of forensic voice comparison testimony in England and Wales

In 2015 the Criminal Practice Directions (CPD) on admissibility of expert evidence in England and Wales were revised. They emphasised the principle that “the court must be satisfied that there is a sufficiently reliable scientific basis for the evidence to be admitted”. The present paper aims to assist courts in understanding from a scientific perspective what would be necessary to demonstrate the validity of testimony based on forensic voice comparison. We describe different technical approaches to forensic voice comparison that have been used in the UK, and critically review the case law on their admissibility. We conclude that courts have been inconsistent in their reasoning. In line with the CPD, we recommend that courts enquire as to whether forensic practitioners have made use of data and analytical methods that are appropriate and adequate for the case under consideration, and that courts require forensic practitioners to empirically demonstrate the level of performance of their forensic voice comparison system under conditions reflecting those of the case under consideration

Perception of natural vowels by monolingual Canadian-English, Mexican-Spanish, and Peninsular-Spanish listeners

On the basis of a previously-reported synthetic-vowel perception experiment, it was hypothesized that the location of the perceptual boundary between Spanish /i/ and /e/ differed for monolingual Peninsular-Spanish and Mexican-Spanish listeners (north-central Spain and Mexico City), and that this would affect the perception of the Canadian-English /i/-/i/ contrast (western Canada): Peninsular-Spanish listeners were predicted to identify almost all tokens of Canadian-English /i/ as Spanish /i/ and almost all tokens of Canadian-English /I/ as Spanish /e/ (two-category assimilation); whereas Mexican-Spanish listeners were predicted to identify almost all tokens of Canadian-English /i/ as Spanish /i/, but identify some tokens of Canadian-English /I/I as Spanish /i/ and some as Spanish /e/. Monolingual Peninsular-Spanish and Mexican-Spanish listeners' perception of natural tokens of English /i/, /I/, /e/, and /ε/ produced by monolingual Canadian-English speakers was tested. Both the Peninsular-Spanish and the Mexican-Spanish listeners had results consistent with the perceptual pattern predicted for the Peninsular-Spanish listeners. The results call into question the assumption that first-language-Spanish learners of English have difficulty learning the English /i/-/I/ contrast because they initially assimilate most tokens of both English vowel categories to a single Spanish vowel category, Spanish /i/

Automatic-type calibration of traditionally derived likelihood ratios:Forensic analysis of Australian English /o/ formant trajectories

A traditional-style phonetic-acoustic forensic-speaker-recognition analysis was conducted on Australian English /o/ recordings. Different parametric curves were fitted to the formant trajectories of the vowel tokens, and cross-validated likelihood ratios were calculated using a single-stage generative multivariate kernel density formula. The outputs of different systems were compared using C llr, a metric developed for automatic speaker recognition, and the cross-validated likelihood ratios were calibrated using a procedure developed for automatic speaker recognition. Calibration ameliorated some likelihood-ratio results which had offered strong support for a contrary-to-fact hypothesis

Avoiding overstating the strength of forensic evidence: Shrunk likelihood ratios/Bayes factors

When strength of forensic evidence is quantified using sample data and statistical models, a concern may be raised as to whether the output of a model overestimates the strength of evidence. This is particularly the case when the amount of sample data is small, and hence sampling variability is high. This concern is related to concern about precision. This paper describes, explores, and tests three procedures which shrink the value of the likelihood ratio or Bayes factor toward the neutral value of one. The procedures are: (1) a Bayesian procedure with uninformative priors, (2) use of empirical lower and upper bounds (ELUB), and (3) a novel form of regularized logistic regression. As a benchmark, they are compared with linear discriminant analysis, and in some instances with non-regularized logistic regression. The behaviours of the procedures are explored using Monte Carlo simulated data, and tested on real data from comparisons of voice recordings, face images, and glass fragments