Forensic linguistics in the Zimmerman case
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The judge in the Zimmerman case has recently decided to let the jury decide for themselves about the source of the screams in the 911 tape ("Jury to decide whose voice on 911 call in Zimmerman case"). This decision is a stinging rebuke to the "expert" testimony of Tom Owen and Alan Reich, and supports the testimony of Peter French, George Doddington, and Hirotaka Nakasone. For a summary of the dueling experts, see Andrew Branca, "Zimmerman Case: Dr. Hirotaka Nakasone, FBI, and the low-quality 3-second audio file", Legal Insurrection 6/7/2013, "Zimmerman Prosecution’s Voice Expert admits: 'This is not really good evidence'", 6/8/2013, and "Zimmerman Case: Experts Call State’s Scream Claims 'Absurd' 'Ridiculous' and 'Imaginary Stuff'", 6/9/2013.
I don't have time this morning to discuss the issues at greater length, but it's clear that the judge's evaluation of the situation was correct.
If you're not familiar with the Speaker Recognition Evaluations (e.g. here and here), or the Language Recognition Evaluations (here and here), that NIST has been running for the past 15 years, you should follow the links above, and take a look at how those projects have been structured.
These programs have been designed to suit the needs of the intelligence community, and are therefore far from a perfect fit to the issues that arise in the courtroom. But there's been enormous progress over the past 15 years, due to the power of the "common task" approach that has had such a striking effect in speech recognition, document retrieval, machine translation, and so on.
It has always seemed strange to me that there's been no comparable effort to put forensic speech and language analysis on a sound quantitative footing. A cynical answer might be that intelligence analysts care about facts and the evidence for them, whereas prosecutors care only about convictions.
Mark P said,
June 24, 2013 @ 10:05 am
I'm afraid you're right about prosecutors caring only about convictions. It seems, unfortunately, that the investigation process is based on finding evidence that supports charges against a particular person rather than finding evidence and then following it wherever it leads.
Jon Weinberg said,
June 24, 2013 @ 1:25 pm
I absolutely trust ML when it comes to the science in this case. All three of the analysis links in the post, though, are to articles written by one Andrew Branca, author of a "guide for the armed citizen" anticipating shooting guns in self-defense, which he advertises with the tagline "Don't get prosecuted for defending yourself and your family. Learn how to stay safe AND out of jail." So I figure that Mr. Branca may be a wee bit less than impartial when it comes to the Zimmerman case.
[(myl) Indeed. A better source would be the YouTube links to the testimony of the five experts involved — but that's something like 8 hours of video. And independent of the qualities of Mr. Branca's socio-political stance, in this case I think his summaries of the testimony are mostly reasonable ones.]
dr. Wiktor Gonet said,
July 1, 2013 @ 10:54 am
I have read the very intersting discussion of the Zimmerman case (thankyou for the links), and found an error in what Prof. P. French is supposed to have said. The text has it:
"We also look at the acoustic resonances within vowel sounds, looking at the frequency with which they occur, the so-called phonemes (…)"
whle what it should say is:
"We also look at the acoustic resonances within vowel sounds, looking at the frequency at which they occur, the so-called formants (…)"
Is my objection right?
dr Wiktor Gonet
Forensic Phonetician, Poland
http://www.fonoskopia.org.pl
gonet@umcs.pl