Researchers measure distinct characteristics in speech of
individuals at high risk of suicide
David F. Salisbury
October 19, 2000
Thirty years ago, Stephen Silverman was a clinical psychologist on the staff of the Brookdale
Hospital Medical Center in New York. As he interviewed patients in the psychiatric emergency
room, Silverman, who is also a jazz pianist, found that the sound of some voices literally caused
the hair on the back of his neck to rise. As he analyzed the voices that created this sense of
alarm, he concluded that it was caused by a distinctive quality in the pattern and tone of the
voices of individuals likely to commit suicide in the near future.
When he went into private practice in Connecticut he became well known for his work with
suicidal and psychotic patients. His wife Marilyn is also a psychologist in private practice and
dealt with some suicidal patients as well. Their experience seemed to confirm the validity of his
earlier observations. So, in the 1980s, the couple decided to investigate the phenomenon on their
own. “I felt we had to answer three questions: What was it that I heard? If I heard it, is it real? And
if it’s real, is it measurable?” Stephen Silverman says.
After years of study and research, the psychologists finally have objective evidence that what he
hears is real and considerable encouragement that it may be measurable as well. An
interdisciplinary research team at Vanderbilt University, working at the Silvermans’ behest, has
identified several acoustic features in the voices of people recorded shortly before they either
took their own lives, or tried to do so without success, that differentiate them from recorded voices
of normal individuals and those suffering from severe depression.
“The research done at Vanderbilt supports the hypothesis that near-term, suicidal voices have
distinct characteristics,” says Marilyn Silverman, “and they support the proposal that this
investigation should be continued with even greater scope and intensity.”
Suicide is currently the eighth leading cause of death in the United States and the third leading
cause of death among 15-24 year olds. More than thirty-thousand people kill themselves every
year and half a million Americans make attempts or threats that require evaluations in hospital
emergency rooms and/or hospitalization. Moreover, suicide rates are on the rise.
One of the biggest problems in suicide prevention is determining the degree of suicide risk of
individual patients. Current assessment methods use personal histories, clinical examination and
psychological testing to judge a person’s risk. Because this kind of information takes a long time
to gather, it is not sufficient for urgent situations that require immediate judgments. So a rapid
method to assess suicidal intent by analyzing the qualities of voice patterns systematically could
be a powerful new tool in the fight to prevent suicidal deaths, the Silvermans maintain.
“The work is promising and has potential clinical value,” says Jo-Anne Bachorowski, assistant
professor of psychology at Vanderbilt, who has been involved in the project. However, she
cautions that a great deal more research must be done before this promise can be realized. “It’s
crucial to recognize that the relationships between tone of voice and any psychological state or
condition are extremely complex. So it is very important to test possible acoustic markers of
suicidality with a wide variety of comparison groups and prospective research designs.”
Early observations and Vanderbilt involvement
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Researchers measure distinct characteristics in speech of
individuals at high risk of suicide
In the early 1980s, the Silvermans began to collect and analyze recorded suicide notes and
interviews made shortly before suicide attempts. Stephen Silverman, who studied with the noted
musician Lennie Tristano and has occasionally played professionally, enlisted the help of a
musician friend to begin identifying and categorizing the qualities that these voices had in
common. They came up with descriptive terms such as dull, lifeless, metallic, hollow, lacking the
sounding board represented by the body. They became convinced that the voice itself—
independent of what a person was saying—contained important information about a person’s
immediate psychological state, including the decision to commit suicide. Friend and collaborator
Ray Terlaga of Litchfield, Conn., performed some preliminary acoustic analyses and the
Silvermans applied for and received three conceptual patents on the idea.
In 1994, the Silvermans visited Vanderbilt and described their project to professors Thomas
Harris, chair of the biomedical engineering department, and Richard Shiavi, an expert in signal
processing. The Vanderbilt researchers agreed to accept the challenge and arranged adjunct
appointments for the Silvermans, who are also affiliated with Yale University. Professor Shiavi
assembled a team of experts, including Bachorowski, Mitchell Wilkes, associate professor of
electrical engineering, and Ralph Ohde, associate professor of hearing and speech, to work on
this unusual problem.
Early analysis was performed by doctoral student Dan France, who is currently a consultant at
the Center for Clinical Improvement at Vanderbilt. One of his first challenges was figuring out how
to deal with the wide variation in quality of the recordings, which were made “in the field” using
tape recorders of varying quality, without the precise control of recordings made in the laboratory.
He analyzed the different recordings and used a variety of techniques to adjust them so they
were fairly uniform in quality.
Differentiating among normal, depressed and suicidal
Once that was done, France analyzed the characteristics of the speech patterns of 34 normal
subjects, 59 suffering from depression, and 22 that were high-risk suicidal. He performed a
“macro” analysis, looking at an array of speech characteristics averaged over 2.5-minute periods
from each subject. He found several features that appear to differ in the voices of normal,
depressed and suicidal individuals.
One of the features involves the dominant frequencies of the voice, called formants, which are
determined by the physical characteristics of the vocal tract. Another involves the power spectral
density of the voice: a measure that quantifies the amount of energy in different frequency
ranges. France found that certain changes in these two features, taken together, correctly
differentiated between depressed and suicidal individuals 80 percent of the time. The results of
his analysis were published in the July 20 issue of the IEEE Transactions on Biomedical
Engineering.
“It’s amazing that we can get such a high level of accuracy, particular given the large variety in
the quality of the recordings that we have to work with,” says Shiavi.
More recently, doctoral student Asli Ozdas has been investigating the second-by-second
variations in the rate of vibration of the vocal chords, called the fundamental frequency. In 10
normal individuals, she found that changes in the fundamental frequency occur relatively
smoothly at this time scale. But in 10 suicidal individuals, she has found a significant increase in
the extent to which the fundamental frequency jitters, or jumps around erratically. The difference
in jitter is pronounced enough to allow her to correctly differentiate suicidal from normal subjects
80 percent of the time, Ozdas reported at the IEEE Conference on Systems, Man and
Cybernetics in Nashville on Oct. 11.
“The jitter result is very interesting and exciting because it is unexpected,” says Marilyn
Silverman. “We don’t know how increased jitter may contribute to what we hear in the voices.”
Need for more recordings and additional study
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Researchers measure distinct characteristics in speech of
individuals at high risk of suicide
Despite such an apparently high detection level, considerably more research is needed to
determine whether acoustic characteristics of this sort can be used as a reliable means for
detecting individuals at high risk of suicide, the researchers agree.
One serious limitation of the current study is the small number of cases that have been analyzed.
Tapes of suicidal individuals are not easy to find. The couple hopes to locate additional
recordings from near-term suicides for future studies. However, they argue that the intense study
of even a small number of “robust” samples has an important role to play this kind of research
effort.
A key problem with any practical detection method is ensuring that the number of “false positives”
and “false negatives” are acceptably low. In this case, a false positive is when the detector
mistakenly identifies a subject as a high-risk suicide. A false negative is where it fails to identify a
high-risk suicide. So, before it can be used for a detection system, the researchers must
determine whether consistent acoustic characteristics accompany suicidal impulses that arise
from different preconditions, such as depression, anger or drugs. They must also ensure that
other mental states do not have the same effects on voice patterns as the decision to commit
suicide.
Plans for increasing size and scope of research
Until now the research has been funded at a relatively low level by private donations that the
Silvermans have collected and by Vanderbilt University. But the psychologists have begun
actively seeking additional sources of funding so that they can increase the project’s size and
scope.
“We are talking about human tragedy,” says Stephen Silverman. “The suicide attempt rate at
universities is very high. It’s becoming an epidemic. We will feel we have done our part if, down
the road, we can help save lives by developing a rapid, non-invasive way to assess suicide risk
that can be used not only in hospital emergency rooms, but also in student health centers or
hotlines where few other resources for assessment may be available.”
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