Feigned depression and feigned sleepiness: A voice acoustical analysis

Abstract

We sought to profile the voice acoustical correlates of simulated, or feigned depression by neurologically and psychiatrically healthy control subjects. We also sought to identify the voice acoustical correlates of feigned sleepiness for these same subjects. Twenty-two participants were asked to speak freely about a cartoon, to count from 1 to 10, and to sustain an “a” sound for approximately 5 s. These exercises were completed three times (within the same testing session) with three differing sets of instructions to the participants. These three conditions were presented in pseudo-random order to control for any order effects, and all subjects were naı̈ve to the intended purpose of this study. For all three conditions, mean speaking rates and pitch ranges were calculated. A series of paired t tests showed significant differences in the speaking rates (counting numbers and free-speech exercises) between the ‘normal’ and feigned sleepy conditions, and between the normal and feigned depression conditions, but not between the ‘sleepy’ and ‘depressed’ conditions. The results for pitch range, for all speech exercises, were not different between the normal and either the feigned depression or feigned sleepiness conditions. These results indicate that persons feigning depression and sleepiness demonstrate some level of conscious control of their speech rate, but they did not convincingly alter their pitch ranges while feigning depression or sleepiness.

Introduction

The literature on the application of quantifiable and objective voice acoustical measures as biomarkers of disease severity and/or treatment response has been growing rapidly in recent years. For example, voice acoustical measures may be sensitive to changes in symptom severity for major depressive disorder (Stassen, Kuny, & Hell, 1998). Since various forms of psychomotor retardation are commonly seen in patients with depression, it is reasonable to suppose that the neuromuscular control of the larynx might also be affected similarly (Nilsonne, 1987). Specifically, since the pitch of voice is determined by the frequency of the vibrations of the vocal folds, which result from activation of the muscles of the diaphragm and larynx (Nilsonne, 1988), narrowed pitch alterations most probably lead to the monotonous speech that is characteristic of individuals with depression (Stassen, Bomben, & Güenther, 1991). Fundamental frequency (F₀) is a measure of this vocal fold vibration frequency, and it corresponds directly to the perceived pitch of the voice (Nilsonne, 1987). As a result, it has become the basis for pitch range analyses.

To measure F₀ of voice, a variety of speech exercises are routinely relied upon, including tasks of automatic speech (e.g., counting from 1 to 10), of free speech (e.g., asking a subject to describe an event), and of reading standard passages. This repertoire of speech exercises is thought to best represent a continuum of speech performance from contrived and acontextual automatic speech to the natural discourse of free speech. Short segments of automatic speech are quick and easy to obtain requiring minimal effort on the part of the subject while providing pertinent data (Nilsonne, 1987). Conversely, free speech elicits more acoustic information via a naturalistic approach for obtaining ecologically valid speech samples. This method is recommended as standard practice for a well rounded examination of voice (cf. Titze, 1995). Other measures elicited from these tasks include: (1) total reading time for a standard passage; (2) the percent pause time per speech sample; and (3) the overall rate of speech. Each of these measures have previously been shown to be altered in the speech of depressed individuals, since common symptoms of depression include diminished prosody of voice, an increase in speech pause time and slower rates of speech (cf. Nilsonne, 1987, Nilsonne, 1988). Ellgring and Scherer (1996) followed 16 patients (11 females, 5 males) with major depressive disorder (MDD) longitudinally, with voice recordings obtained via a structured interview conducted twice per week over the duration of their clinical treatment. These results showed that the rate of speech increased markedly over the transition from depressed to non-depressed in patients who were successfully treated for MDD. The mean duration of pauses also decreased with treatment between 56 and 59 percent, and the average number of pauses per interview declined between 25 and 32 percent over the course of treatment.

The purpose of the present study was to determine, how neurologically and psychiatrically healthy individuals alter their speech, as measured by several of the aforementioned voice acoustical metrics, in order to simulate, or feign depressed mood. We also sought to answer the same set of questions for simulated sleepiness. One future goal of this work is to determine whether such individuals can modify their voice in a manner that is identical to that found for patients with documented MDD. However, the absence of raw data for MDD patients prevented direct comparisons to our feigning data at the present time. Future studies will implement tasks of a comparable nature in order to make direct comparisons between the acoustic characteristics of feigners and genuinely depressed individuals.