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Normative Study of 192 Healthy Volunteers

Nonverbal Information Contained in Human Speech

As basis of our investigations into the nonverbal information contained in human speech, we have carried out a normative study with 192 healthy volunteers, stratified according to age, sex and education. The specific design of this study with 3 different types of text and 2 repeated measurements at 14 day intervals has been particularly chosen in order to analyse the reproducibility of the major speech parameters as well as their sensitivity to form and content of spoken text. In addition, we wanted to derive reference values of the general population and to learn to distinguish between normal fluctuations and significant changes over time.

Principal Goals

Specifically, the principal goals of this study were: (1) determining an optimum recording time containing enough information for a reliable estimation of speech parameters, (2) determining the distribution of the inter-individual scattering of speech parameters in the general population, (3) determining the intra-individual stability of speech parameters over time (in order to learn to distinguish between normal fluctuations and significant changes), (4) determining possible differences in the speech parameters between dialect and non-dialect, and between affect-neutral and affect-charged speech, (5) determining the amount of variance explainable by the external factors age, sex and social status, and (6) developing a practical procedure which is free of interactions during recording and which can easily be carried out in a standard form by a technician.

Speech Recordings

The test persons were first informed about the goals of the study as well as about the procedure to follow. Subsequently, the persons were asked to fill out the BfS questionnaire [von Zerssen 1987] which measures his momentary emotional state. Immediately following this, the test persons were led to the recording studio where they were asked to count loud from 1 to 40 and to present their personal history free-hand in their native dialect and with their normal voice. This procedure took about 2 minutes and was used to calibrate the recording. After voice calibration, a well-defined tone of 5 seconds duration was recorded on tape for the calibration of loudness. Under the assumption that this counting and free-hand speaking helped the test persons to relax, the actual measurement was carried out according to the following plan:

  • Counting out loud from 1 to 40 and free-hand presentation of personal history in native dialect (about 2.5 minutes)
  • Short pause (maximum 0.5 minutes)
  • Emotionally neutral text from a well-known children's book to be read out loud in High German (about 3 minutes)
  • Short pause (maximum 0.5 minutes)
  • Emotionally stimulating text from a well-known author to be read out loud in High German (about 3 minutes)
  • Counting out loud from 1 to 40

scatter plot
Fig. 3a: Stability of speech parameters "mean vocal pitch" and "6db-bandwidth" as a function of time (healthy volunteers): the first assessment is plotted along the x-axis and the second assessment 14 days later along the y-axis.

While mean vocal pitch displays a high stability over time, the speech parameter "6db-bandwidth" (measuring intonation) is much less stable. The experimental condition is "counting/frehand speech" and the sample comprises 91 healthy subjects.
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