Listeners can recognise the emotional state of a speaker. But
what are the acoustic characteristics of the speech which express
fear, happiness or sadness? Scientists at the TU Berlin have now
analysed these traits and incorporated them in a computer-generated
When the German SPD was selecting a new leadership in 1995, Walter
Sendlmaier could hear that Rudolf Scharping had no chance against
Oskar Lafontaine. And something else came to his ear, namely the
voice of Gerhard Schröder. He gave him the greatest chance
of becoming the next chancellor. But the scientist wasn't studying
the speeches out of political interest - he was more concerned
with analysing the politicians' voices and the effects they had.
The communications researcher at the Technical University (TU)
Berlin investigates the way in which basic emotions such as happiness
or fear are expressed, and the features of voice and expression
which allow listeners to recognise these emotional states. It
is not at all clear which acoustic characteristics allow us to
identify the annoyance of Lafontaine, the resignation of Scharping,
or the belligerence of Schröder. The Berlin Institute of
Communications, Media and Musical Science is one of the few scientific
institutions studying emotion in vocal expression.
The experiments involved actors in a sound studio repeating sentences
with neutral contents in either a bored, sad, happy, disgusted,
or frightened way. If at least 80% of a group of listeners assigned
the intended emotion to a sentence, this sentence was analysed
syllable by syllable. "We looked at features such as pitch,
volume, basic frequency of the voice, and speed of talking, and
also the accuracy of articulation, which has received very little
attention in the past" commented Prof. Sendlmaier, whose
research work is being funded by the DFG (Deutsche Forschungsgemeinschaft).
The scientists came up with some surprising results: Angry or
happy people speak very quickly, and it would be natural to suppose
that this involved leaving out or blurring syllables in words.
But this is not at all the case when anger is concerned: "We
not only speak quicker but also more clearly. In this state we
emphasise very many syllables, which leads to improved articulation",
explains the scientist.
In cases of boredom, sadness or fear it is possible to identify
the opposite effect. "Although we speak more slowly in such
cases, the syllables are articulated less clearly, because we
generate the sounds with the lower jaw open at a smaller angle."
Our body tenses up, and we can hardly open our mouth for fear.
In contrast, when we are happy or angry we swing our arms, our
thorax is pushed forward, and we open our mouth wide. As a result
the words are articulated much more clearly.
There are also noticeable differences in pitch. In a state of
fear the voice can rise by up to an octave, and we speak in a
falsetto; at the same time the speech melody becomes more monotonous.
The explanation for this is to be found in the activity of the
muscles in the larynx, which control the vibrations of the vocal
chords. In the state of anger they contract much more abruptly
than with other emotions, and more energy goes into the higher
overtones. These changes in the tone colour are clearly noticeable
to the listener. In the case of sadness, however, the movements
of the vocal chords are much gentler, and they often barely touch.
The air escaping between them produces vortices, giving the voice
a distinctive aspirated sound.
In order to test the results, the TU scientists programmed a computer-generated
voice with these characteristics. If the test listeners are able
to identify the correct emotional state for the artificial voice,
"then we have probably found the right indicators" says
the acoustic researcher. A sign of the potential of "smiles
that you can hear" is the numbers of enquiries received,
particularly from companies in the fields of automatic speech
recognition and speech synthesis.
Contact: Prof. Walter Sendlmaier, TU Berlin, Institute
of Communications, Media and Musical Science
Special field: Verbal communication and phonetics
Research project: Phonetic reduction and elaboration
during emotional expression (DFG Project Se 462/3-1)
Address: Einsteinufer 17, 10587 Berlin, Tel: +49
30 314-24503, E-mail: firstname.lastname@example.org
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