Doctoral student Asli Ozdas analyzes the smallest variations in the voice patterns of individuals at high risk of suicide.

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 attempt suicide in the near future.
       Following full time hospital practice, Silverman went into private practice in Connecticut and continued his clinical work with suicidal and psychotic patients. His wife Marilyn, also in the private practice of psychotherapy, has had extensive experience with suicidal younger 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 said.
       After years of study and research, the clinicians 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 who are not suicidal.
       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 30,000 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 greatest 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 work is promising and has potential clinical value," said Jo-Anne Bachorowski, assistant professor of psychology at Vanderbilt, who has been involved in the project. However, she cautioned 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."

A meeting of the minds: husband and wife psychologists Stephen and Marilyn Silverman (front) huddle in late February with Vanderbilt engineering team members Professor Richard Shiavi, graduate student Asli Ozdas and Associate Professor Mitchell Wilkes (back, left to right) to discuss progress and next steps for their research efforts.

Silvermans begin project
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 and 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.

Vanderbilt gets involved
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 on the clinical faculty of the Yale University School of Medicine. 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.

Macro-analysis provides accurate identification
Once that was done, France analyzed the characteristics of the speech patterns of 34 normal subjects, 59 suffering from depression and 22 that were near-term, 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.

Early results of micro-analysis reported
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," said Marilyn Silverman. "We don't know how increased jitter may contribute to what we hear in the voices."

Need for additional study
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 near-term high risk of suicide, the researchers agree.
       The question has been raised as to whether the relatively small sample size represents a serious limitation of the current study. The Silvermans do hope to locate additional recordings for future studies. However, many behavioral scientists maintain that the intensive study of a small number of robust clinical samples has an extremely important role to play in this kind of research effort.
       A key problem with any practical detection method is ensuring that the numbers 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 and by Vanderbilt. But the clinicians have begun actively seeking additional sources of funding to increase the project's size and scope.
       "We are talking about human tragedy," said 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 contribute to the assessment of near-term 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."