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Forensic voice evidence

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Hughes, V. (2017) Forensic voice evidence. Diploma Course in Forensic Human Identification (organised by Peter Vanezis), Queen Mary University, London, UK. 9 March 2017.

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Forensic voice evidence

  1. 1. Diploma course in Forensic Human Identification (DipFHI) 9th March 2017 Forensic Voice Evidence Dr Vincent Hughes vincent.hughes@york.ac.uk
  2. 2. • the voice as evidence • types of voice evidence – forensic voice comparison – speaker profiling – earwitnesses – disputed utterances • the future for voice evidence Overview DipFHI 9th March 2017
  3. 3. The voice as evidence
  4. 4. Forensic speech science (FSS)… “... the application of the knowledge, theories and methods of general phonetics (and increasingly, speech technology) to practical tasks that arise out of a context of police work or the presentation of evidence in court, as well as the development of new, specifically forensic (…), knowledge, theories and methods” Jessen (2008: 671) The voice as evidence DipFHI 9th March 2017
  5. 5. • first admitted in UK courts in 1960s (Ellis, 1990) • now… > 600 cases a year (French, 2017) involving voice evidence – PACE (1984) – development of FSS as a field – availability of (half decent) speech recordings The voice as evidence DipFHI 9th March 2017
  6. 6. • the voice is an extremely difficult form of forensic evidence The voice as evidence DipFHI 9th March 2017 1. inherent limitations of the voice as a biometric
  7. 7. The voice as evidence DipFHI 9th March 2017 ≠
  8. 8. • the voice is an extremely difficult form of forensic evidence The voice as evidence DipFHI 9th March 2017 1. inherent limitations of the voice as a biometric 2. forensically realistic materials
  9. 9. • speaker factors: – modalities (shouting, whisper…) – emotion – Intoxication… • technical factors: – telephone transmission – mobile codecs… • situational factors: – overlapping speech – background noise… The voice as evidence DipFHI 9th March 2017
  10. 10. • UK experts: linguistic phonetic methods – auditory and acoustic analysis – detailed IPA transcription – combined with acoustic measurements (R v O’Docherty [2002]) • consonants • vowels • pitch (f0) • voice quality (timbre) • rhythm • speech rate • lexical choices • hesitation phenomena see French et al. (2010) • etc. The voice as evidence DipFHI 9th March 2017
  11. 11. Forensic voice comparison
  12. 12. Forensic voice comparison DipFHI 9th March 2017 known suspect vs. unknown offender
  13. 13. Right. Yeah, he mentioned … Right. Mm actually I don't have my driver’s licence. From Leeds yeah. Canada. No, that's what I thought it was. F- f- I felt it. I thought I had it. (?) no I did not steal the car. No, I don't have it, mate. Don't have it, mate. Are you sure it's coming out stolen? Did it come out? Wh- wh- what do y- what did you go by? (Yeah). Where was it stolen? What's he need now? Can you roll this window down a bit, I'm just claustrophobic. I'm on medication for it. Pardon? Can you let me out for a sec, I've got- I'm on medication for claustrophobia and anxiety. Pardon? Just- just the window down or something. What we waiting on? What we waiting on? Got to wait for vehicle recovery? DipFHI 9th March 2017 Example case (1)
  14. 14. Hey mate can you give me an update on the rugby union um the um Munster versus Trevis(o)- T X thirty five thirty one five. And eh college basketball uh Florida versus Louisville. And could you tell me how much time’s left please? Florida and Louisville. OK cheers mate. Hey mate. College basketball. Oregon. T X thirty five thirty one five. (that’s ?) uh just gimme an update how much time’s left. So Oregon… you know… you guys are betting on it. Seventy fifty two. Cheers mate. Hello mate. Could you- can you give me an update on the uh Gwent versus Leicester rugby union score? T X thirty five thirty one five. Right… DipFHI 9th March 2017 Example case (1)
  15. 15. DipFHI 9th March 2017 Offender (video track) Suspect (betting calls) rhoticity intervocalic (t) tapped mate (lexis + [eː]) monophthongal[oː] Example case (1)
  16. 16. • unusual mix of US and Yorkshire features – consistency across samples (similarity) – extremely small number of people who could have produced this evidence (typicality) • David Bieber, a.k.a. Nathan Coleman • voice evidence crucial – denied murder - no comment interview – sentence to life imprisonment DipFHI 9th March 2017 Example case (1)
  17. 17. Expressing conclusions: the past… Forensic voice comparison DipFHI 9th March 2017 starting point binary decision yes no 1990s classical probability scales Broeders (1999: 229) French and Baldwin (1990: 10) positive negative 2007 UK position statement French and Harrison (2007) Rose and Morrison (2009)
  18. 18. Forensic voice comparison DipFHI 9th March 2017 Expressing conclusions: the present and future… p(E|Hp) p(E|Hd)LR = FVC Hp prosecution Hd defence
  19. 19. • issues and opportunities (Gold and Hughes, 2014; Hughes, 2014; Hughes and Wormald, in press) – statistical models – definition of the relevant population – availability of background data – combination of results from different features Forensic voice comparison DipFHI 9th March 2017
  20. 20. Speaker profiling
  21. 21. • investigative application – e.g. ransom demands, threatening calls • information that can be dervied… – regional, social, educational background – age – ethnicity/ second language influences – speech pathologies – read vs. spontaneous speech – location – influence of intoxicants – attempts at disguise Speaker profiling DipFHI 9th March 2017
  22. 22. • ‘Wearside Jack’ – Yorkshire Ripper: multiple murders in 1970s/80s – letters & tape sent to ACC George Oldfield (West Yorkshire Police) – apparent confession by man claiming to be ‘Jack’ – tape analysed by Ellis (see Ellis 1994) Example case (2) DipFHI 9th March 2017
  23. 23. Example case (2) DipFHI 9th March 2017 /h/-dropping isogloss pronunciation of PRICE vowel: time, strike (cf. Tyneside [ɛi]~[ɑi] alternation in knife, knives, etc.)
  24. 24. • ‘Wearside Jack’ – major change in focus of investigation – Peter Sutcliffe: Bradford (Yorkshire) accent Example case (2) DipFHI 9th March 2017 • ‘Wearside Jack’ – major change in focus of investigation – Peter Sutcliffe: Bradford (Yorkshire) accent – Hoaxer remained at large until 2005 – John Humble arrested – Convicted for 8 years – see French et al. (2006)
  25. 25. • ‘Lord Buckingham’ – arrested entering UK on false passport – claimed to be English Lord from London – but… • title ‘Lord Buckingham’ lapsed in 18th C. • adopted name and DOB of dead child – jailed for 9 months where to send him upon release? Example case (3) DipFHI 9th March 2017
  26. 26. • phonetic analysis – sporadic post-vocalic /r/ (‘rhoticity’) – e.g. four, hire yod-dropping – e.g. news, institutions – vowel quality – e.g. /æ/ in after rather than expected /ɑː/ – stress patterns – e.g. kilometres – pronunciation of proper names – e.g. Buckingham Example case (3) DipFHI 9th March 2017
  27. 27. Other forms of voice evidence
  28. 28. • judgement made by lay listener • may need to show their ability to recognise the voice: voice line-up (vocal equivalent of visual line up) • but… – methodological issues with their set up (Nolan and Grabe, 1996; Nolan, 2003; Nolan et al., 2013) – expensive and time consuming Earwitnesses DipFHI 9th March 2017
  29. 29. • not who is talking… but what is being said • usually… – a small section (a sound or a syllable) with high evidential value – noisy section (lots of background noise) Disputed utterances DipFHI 9th March 2017
  30. 30. • David Bain What’s being said? Is it even speech? Example case (4) DipFHI 9th March 2017 Bain: Yes [heavy breathing] [DISPUTED MATERIAL] Op: What number are you calling from? Bain: Four...
  31. 31. Where are we now?
  32. 32. Improving methods • increasing focus on automatic speaker recognition (ASR) systems – holistic analysis of entire speech signal Where are we now? ü û efficient; easy to process masses of data ‘black box’ perception error rates difficult to explain to courts viewed as more scientific/objective poorer performance under real forensic conditions perform extremely well under certain conditions require relatively long samples and large amounts of background data
  33. 33. Improving methods • integrating the best bits of linguistics and ASR – courts increasingly accepting both (e.g. Germany, Sweden) Where are we now? • Cc – linguistic-phonetic information can help resolve errors made by ASRs • hesitations (errs and erms) (Hughes, Foulkes and Wood, 2016) • voice quality (Hughes et al., in press)
  34. 34. Validation and regulation • empirical testing using numerical LRs since early 2000s – small number of features – forensic realism? • increasing focus on the importance of validation and regulation • falling in line with paradigm shift across forensic science Where are we now? DipFHI 9th March 2017 https://www.gov.uk/government/uploads/system/ uploads/attachment_data/file/482631/FSR-C- 134_Draft_Audio_Appendix.pdf
  35. 35. • the voice commonly used as evidence – many different applications – 600+ cases per year • significant progress in the last 20 years across forensic phonetics and speech technology – improvement in the quality of forensic voice evidence presented to courts – still many areas for development – complexity of speech = opportunity Conclusions DipFHI 9th March 2017
  36. 36. Want to know more? • email me: vincent.hughes@york.ac.uk • check out our MSc in Forensic Speech Science: https://www.york.ac.uk/language/postgraduate/taught/forensic-speech-science/ • check out our CPD courses in Forensic Speech and Audio: https://www.york.ac.uk/language/cpd-courses/ Thank you! Questions?
  37. 37. Ellis, S. (1990) It's getting rather serious ... early speaker identification. In H. Kniffka (ed.), Texte zu Theorie und Praxis forensicher Linguistik. Tübingen: Max Niemeyer. Ellis, S. (1994) The Yorkshire Ripper enquiry: part I. Forensic Linguistics 1(2): 197-206. French, J. P. (2017) A developmental history of forensic speaker comparison in the UK. English Phonetics 21. French, J. P. and Harrison, P. (2007) Position statement concerning the use of impressionistic likelihood terms in forensic speaker comparison cases. International Journal of Speech, Languageand the Law 14(1): 137-144. French, J. P. et al. (2010) The UK position statement on forensic speaker comparison: a rejoinder to Rose and Morrison. International Journal of Speech, Languageand the Law 17(1): 143-152. Gold, E. and French, J. P. (2011) International practices in forensic speaker comparison. International Journal of Speech, Language and the Law 18(2): 293-307. References
  38. 38. Gold, E. and Hughes, V. (2014) Issues and opportunities: the application of the numerical likelihood ratio framework to forensic speaker comparison. Science and Justice 54(4): 292-299. Hughes, V. (2014) The definition of the relevant population and the collection of data for likelihood ratio-based forensic voice comparison. Unpublished PhD thesis, University of York, UK. Hughes, V. and Wormald, J. (in press) Justice needs you: the importance of greater collaboration between sociolinguistics, phonetics and forensic speech science. Language and Linguistics Compass. Nolan, F. (2003) A recent voice parade. International Journal of Speech, Language and the Law 10(2): 277-291. Nolan, F. and Grabe, E. (1996) Preparing a voice line-up. Forensic Linguistics 3(1): 74-94. Nolan, F. et al. (2013) Effects of the telephone on perceived voice similarity: implications for voice line-ups. International Journal of Speech, Language and the Law 20(2): 229-246. References
  39. 39. Rose, P. and Morrison, G. S. (2009) A response to the UK position statement on forensic speaker comparison. International Journal of Speech, Language and the Law 16(1): 139-163. References

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