Poster B74, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
Pitch, Formants, and Formant Differences are Decisive Factors in Vowel Processing – Electrophysiological Evidence from N1 Amplitude and Latency Analyses.
Marina Frank1, Beeke Muhlack1, Franka Zebe1, Mathias Scharinger1;1Philipps University Marburg
Introduction: Vowels in spoken language combine pitch and spectral properties, both of which seem to determine neural processing, as evidenced by the N1. The N1 is a negative evoked potential measured by electroencephalography (EEG) peaking at around 100 ms after the onset of an auditory stimulus. The purpose of this study is to investigate the role of the N1 in vowel processing. To be precise, we were interested in the factors influencing the N1 component, namely the perceived pitch and spectral features. In order to analyze the contribution of pitch, the stimuli used in this study were manipulated in fundamental frequency. Thus, the factors under investigation were f0, F1, F2, and the distance between F1 and F2. The impact of these factors on amplitude and latency of the N1 peak were analyzed. Methods: We conducted an EEG experiment with 20 native speakers of German. The stimuli consisted of six different vowels of the German vowel inventory which were manipulated in fundamental frequency. We additionally used three sinusoidal tones as a control condition. Subjects were asked to listen to the vowels and to press a button on a response box when hearing a (pseudo-randomly inserted) friction noise. This task ensured the attention of the subjects. The EEG data from 32 electrodes were processed in MATLAB. Results: Overall, the pattern of results demonstrated that f0 only has an influence on the latency of open vowels (e.g. [a]), but not of closed vowels (e.g. [i]), while F1 influenced both amplitude and latency of all vowel categories. F2 as well as the distance between F1 and F2 correlated significantly with the amplitude but not with the latency. The amplitude and latency of the N1 of the three pure tones was not significantly affected by differing pitches. Conclusion: This study supports the hypothesis that f0 is not as relevant as other factors, i.e. formant values, in vowel processing. This was tested using three pure tones as control condition. Pitch only showed effects regarding the latency of the N1, while F2 only correlated with its amplitude. Thus, F1 is a factor that is more relevant for both amplitude and latency of the N1 peak. However, the strongest correlation concerning the amplitude was the distance between F1 and F2. The results are in line with well-known research in phonetics, namely the importance of F1 and F2 for vowel discrimination. Within the epoch of the N1 component, vowels are processed on the basis of their spectral features. We found evidence that the (intrinsic) vowel pitch is not as relevant for the N1 as the distance between the first two formants. The results from the current study form an important contribution to research on pitch vs. spectral processing in spoken language.
Themes: Speech Perception, Perception: Auditory
Method: Electrophysiology (MEG/EEG/ECOG)