Abstract
In laryngeal high-speed videoendoscopy (HSV) the area between the vibrating vocal folds during phonation is of interest, being referred to as glottal area waveform (GAW). Varying camera resolution may influence parameters computed on the GAW and hence hinder the comparability between examinations. This study investigates the influence of spatial camera resolution on quantitative vocal fold vibratory function parameters obtained from the GAW. In total 40 HSV recordings during sustained phonation (20 healthy males and 20 healthy females) were investigated. A clinically used Photron Fastcam MC2 camera with a frame rate of 4000 fps and a spatial resolution of 512×256 pixels was applied. This initial resolution was reduced by pixel averaging to (1) a resolution of 256×128 and (2) to a resolution of 128×64 pixels, yielding three sets of recordings. The GAW was extracted and in total 50 vocal fold vibratory parameters representing different features of the GAW were computed. Statistical analyses using SPSS Statistics, version 21, was performed. 15 Parameters showing strong mathematical dependencies with other parameters were excluded from the main analysis but are given in the Supporting Information. Data analysis revealed clear influence of spatial resolution on GAW parameters. Fundamental period measures and period perturbation measures were the least affected. Amplitude perturbation measures and mechanical measures were most strongly influenced. Most glottal dynamic characteristics and symmetry measures deviated significantly. Most energy perturbation measures changed significantly in males but were mostly unaffected in females. In females 18 of 35 remaining parameters (51%) and in males 22 parameters (63%) changed significantly between spatial resolutions. This work represents the first step in studying the impact of video resolution on quantitative HSV parameters. Clear influences of spatial camera resolution on computed parameters were found. The study results suggest avoiding the use of the most strongly affected parameters. Further, the use of cameras with high resolution is recommended to analyze GAW measures in HSV data.
Highlights
Regardless of the area of research, small factors can often exert a strong influence on the results obtained and the parameters calculated
We investigate the influence of changing spatial resolution on 50 different potential glottal area waveform (GAW) parameters
Each circle is the relative deviation between SR3 and spatial resolution of 512×256 pixels (SR1) parameter values
Summary
Regardless of the area of research, small factors can often exert a strong influence on the results obtained and the parameters calculated. The vocal folds are set in motion by a stream of air rising from the lungs. This results in a periodic oscillation of the vocal folds cyclically interrupting the airflow in the process producing audible sound [5, 6]. Different ranges of the frequency of vocal fold oscillation are given in literature with upper boundaries ranging from about 250 Hz [7, 8] to 400 Hz [9] in females. While the vocal folds are the vibratory sound source [13], the sound is further modulated by tongue and lips generating the audible voice and speech [5, 6]
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