## Materials and Methods
### Data Collection
To reduce the uncertainty in collision pressure measurements by the ISP probe, the sensors were embedded in medical-grade room-temperature-vulcanizing (RTV) silicone and covered with a thin 0.125 mm silicone sheet to create a flat contact surface [12; 13]. The five data channels were each digitized at 8000 samples per second and 16-bit quantization by a digital acquisition board (6259 M series, National Instruments, Austin, TX, USA). Gain control and anti-aliasing filtering was set by preconditioning electronics (CyberAmp model 380, Danaher, Corp., Washington, DC, USA). Time synchronization ofthe high-speed video data and data channels was accomplished by a common clock source from the National Instruments board that supplied the 2000 Hz (video) and 8000 Hz (data) sampling signals. Two of the alternating current (AC) signals were calibrated using linear scaling factors to convert from voltage levels to units of pascals for the microphone signal [43] and units of cm/\(s^{2}\) for the neck-surface accelerometer signal. The AC electroplotography signal was left unclibrated as a relative measure vocal fold contact. Calibration of the ISP probe's pressure sensors accounted for the sensor silicone enclosures by submerging the probe in a graduated cylinder filled with water and noting the voltage level at given submergence depths for each sensor (i.e., hydrostatic pressure) and computing a best-fit line to the data (coefficient of determination for the line was 1.0). The linear, multiplicative scale factors that mapped pressure sensor voltage levels (V) to units of pressure (cm H\({}_{2}\)O) were stable and repeatable at 1.596 (cm H\({}_{2}\)O)/V for the intraglottal pressure sensor and 1.722 (cm H\({}_{2}\)O)/V for the subglottal pressure sensor. The DC level of the intraglottal and pressure signals exhibited a low-frequency component (DC drift) also observed in prior in vivo studies that was associated with thermal fluctuations [8; 9]. Zero subglottal pressure was defined during the silence period prior to the onset of phonation (3.4 cm H\({}_{2}\)O correction factor was subtracted from the measured signal), and the intraglottal zero pressure level was defined at the most-negative peak pressure value [13] when the intraglottal sensor was positioned in the plane of vocal fold collision during phonation (1.3 cm H\({}_{2}\)O correction factor was added to the measured signal). Endoscopic visualization of the larynx during sustained phonation at comfortable pitch and loudness levels allowed the endoscopist to place the dual-sensor pressure probe such that the proximal sensor was positioned intraglottally and the distal sensor subglottally. The clinician held a left-handed ISP probe with pressure-sensing elements facing the functioning left vocal fold of the participant. As recommended in prior work [13], it was necessary to ask the subject to produce sustained phonation while the ISP probe was slowly swept in the superior-inferior dimension. Then, during the data analysis phase, features related to vocal fold collision were then identified to determine when adequate vocal fold contact occurred to capture peak collision pressures. Figure 3 displays high-speed videoen-doscopic images from one phonatory cycle during which the proximal pressure sensor of the ISP probe was deemed to be positioned in the strike zone of vocal fold collision. Video  
Figure 2: In vivo intraglottal/subglottal pressure (ISP) probe with two pressure sensors at the probe tip to simultaneously measure intraglottal and subglottal pressure during phonation, (**a**) ISP probe with a Ford injector-like handle and two-channel signal conditioning electronics, (**b**) zoomed-in view of the ISP probe tip showing dimensions of the two in-line pressure sensors. From [13].