title: Comparing Chalk With Cheese-The EGG Contact Quotient Is Only a Limited Surrogate of the Closed Quotient.
abstract: The electroglottographic (EGG) contact quotient (CQegg), an estimate of the relative duration of vocal fold contact per vibratory cycle, is the most commonly used quantitative analysis parameter in EGG. The purpose of this study is to quantify the CQegg's relation to the closed quotient, a measure more directly related to glottal width changes during vocal fold vibration and the respective sound generation events. Thirteen singers (six females) phonated in four extreme phonation types while independently varying the degree of breathiness and vocal register. EGG recordings were complemented by simultaneous videokymographic (VKG) endoscopy, which allows for calculation of the VKG closed quotient (CQvkg). The CQegg was computed with five different algorithms, all used in previous research. All CQegg algorithms produced CQegg values that clearly differed from the respective CQvkg, with standard deviations around 20% of cycle duration. The difference between CQvkg and CQegg was generally greater for phonations with lower CQvkg. The largest differences were found for low-quality EGG signals with a signal-to-noise ratio below 10 dB, typically stemming from phonations with incomplete glottal closure. Disregarding those low-quality signals, we found the best match between CQegg and CQvkg for a CQegg algorithm operating on the first derivative of the EGG signal. These results show that the terms "closed quotient" and "contact quotient" should not be used interchangeably. They relate to different physiological phenomena. Phonations with incomplete glottal closure having an EGG signal-to-noise ratio below 10 dB are not suited for CQegg analysis.
authors.affiliation: Bioacoustics Laboratory, Department of Cognitive Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria. Electronic address: herbst@ccrma.stanford.edu.
authors.forename: Christian T
authors.initials: CT
authors.lastname: Herbst
authors.affiliation: Voice Research Lab Groningen, Wasaweg 9, 9723 JD Groningen, The Netherlands.
authors.forename: Harm K
authors.initials: HK
authors.lastname: Schutte
authors.affiliation: Bioacoustics Laboratory, Department of Cognitive Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Bowling
authors.affiliation: Voice Research Lab, Department of Biophysics, Faculty of Science, Palacký University Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic.
authors.forename: Jan G
authors.initials: JG
authors.lastname: Svec
mesh_terms: D000465:Algorithms; D004568:Electrodiagnosis / Q000379:methods*; D005260:Female; D006801:Humans; D007734:Kymography / Q000379:methods*; D007830:Larynx / Q000502:physiology*; D008297:Male; D063346:Singing
keywords: Closed quotient; Contact quotient; EGG; Electroglottography