Baumeister, Barbara Susanne
Akustische und perzeptive Analysen von Sprache unter Alkoholeinfluss.
Dissertation, LMU München: Faculty for Languages and Literatures
In this thesis, several acoustic and perceptive studies on the influence of alcoholic intoxication on speech are presented. The speech samples for the experiments are taken from the Alcohol Language Corpus, a large database containing recordings of 162 (77 female and 85 male) speakers in both sober and intoxicated conditions with various blood alcohol concentrations. An acoustic analysis of recordings of 148 speakers in intoxicated and sober condition reveals a significant increase of the mean and also of the interquartile ranges of the fundamental frequency in the majority of speakers. A large inter-speaker variability was found, but no correlation with their individual blood alcohol concentration. An analysis of the microperturbation parameters jitter and shimmer in the vowels /a:/ and /i:/ showed no consistent results and a large variance among the data. Jitter is significantly lower in intoxicated condition but only in the vowel /a:/. Shimmer is found to be significantly higher in intoxicated condition but only for male speakers in the vowel /a:/ and in read speech of male speakers in the vowel /i:/. Additionally, a forced choice discrimination test was conducted with speech samples of 161 speakers. 71 naive listeners reached an average discrimination rate of 63,1% which is well above chance. No gender-dependent effects could be found. The ability of the listeners to pick the correct stimulus was higher for speakers with high blood alcohol concentrations, with no connection to the drinking habits of the speakers. To see, whether fundamental frequency also functions as a perceptual cue to reveal a person’s intoxication solely by the speech signal, the results of the perception test were compared with the acoustic measurements of fundamental frequency of the speakers. Those who tend to use higher fundamental frequency in intoxicated condition were judged correctly more often. Similar results could be found for speakers who use larger pitch ranges. The listeners also showed a general preference for the stimulus with higher fundamental frequency and higher pitch range. To further test fundamental frequency as a perceptual cue, two perception tests with manipulated stimuli were conducted. In the first one, the fundamental frequency effects in the stimulus in intoxicated condition were compensated by adjusting mean fundamental frequency and the interquartile range of the intoxicated stimulus to that of the sober stimulus in each discrimination pair. In the second one, fundamental frequency effects were simulated in a sober stimulus and compared to another sober stimulus in one pair. The simulation of fundamental frequency effects was performed by up-shifting and stretching the contour by 5%, according to the findings in the acoustic study. In the test with compensated fundamental frequency effects, listeners did not perform worse than in the basis test. In the second test with simulated fundamental frequency effects, they show a slight tendency to pick the manipulated stimulus as the intoxicated one. Fundamental frequency seems not to function as a strong perceptual cue for listeners in revealing a person’s intoxication, maybe changes of fundamental frequency occur as a side-effect of other effects that play the major role. These could be due to other acoustic features and/or maybe linguistic or paralinguistic information. Listeners may use fundamental frequency as kind of
a fall-back feature if no other signs of intoxication are present as is the case in the test with simulated effects. Probably listeners do not rely on fundamental frequency as a perceptual cue, because it is also prone to changes caused by other speaker states.