Date: 06/27/2021

Stefano Coretta from the University of Edinburgh has a wide range of knowledge in statistical analyses and research methods in linguistics research. Today we had him walk us through how to operate the EGG machine, apply it in the practical study and process the data.

Anatomy

We firstly started with the anatomy of larynx. 

1. When making voiced sounds, the vocal cords would contact and dispart over time. 
2. The frequency of vocal-fold vibration varies between sounds and speakers. For the same sound, if produced in certain distinctive voices, like in creaky or breathy voices, the vocal folds would vibrate differently, which can be measured by the EGG. 

Electroglottography

We learned about the principles of the EGG and got the chance to see how to use the machine.

1. The principle of EGG is that there are two metal signal-receiving tabs, which would be put against the neck skin. When the two larynges contact each other, the current is allowed to pass, which would be recorded as waveforms. 
2. The maximum of the EGG signals corresponds to the close phase of the glottis, and the minimum corresponds to the open phase of the glottis.
3. The EGG can be used to measure

• Robust estimation of fundamental frequency (f0).
• Detection of voiced/voiceless intervals.
• Voice quality via Contact Quotient (CQ): higher CQ = creakier voice, lower CQ = breathier voice.
• Vocal Folds configuration via complex methods like wavegram.

4. The limitation of the EGG is that it only works when there is vocal fold vibration and shows no information when there is a voiceless interval.

Analysing the EGG signal

There are various ways to analyse the EGG data, which can be processed on different platforms, including Praat, R, Matlab, Python and so on. To process the EGG signal, what usually needs to be done are:

• Pre-processing

       – Filtering

       – Calculate the first derivative (dEGG)

• Extract measurements

       – Contact Quotient (ratio between closed phase and glottal cycle)

       – Wavegram (Herbst 2010)

• Analyse measurements

       – WaveGAMs (Coretta 2019)

Calculate measurements

We can get various measurements with the use of different tools. For example:

In Praat:

1. Get maxima and minima of the dEGG.
2. Calculate the glottal period.

In R:

1. Calculate the Contact Quotient.
2. Calculate f0.

Reflections from our Research Group

• Our group has long been exploring different quantitative research methods and data analyses in linguistics. This workshop is very relevant to what we are pursuing.
• It gave us a clear understanding of using the EGG.
• This gave us the confidence to look at glottal movements in our research.