DOI: 10.5061/dryad.73n5tb356
title: Vocal membranes lower the phonation threshold pressure in rhesus macaques (Macaca mulatta)

description: The vocal membrane is present in a wide range of species including
 non-human primates. It has been a matter of great interest how this small
 tissue contributes to the animal vocalizations and its evolutionary loss
 facilitated the speech communication in humans. There has been a
 theoretical study (Mergell et al., 1999), which predicted that the vocal
 membranes make the animal vocalizations more efficient by lowering the
 phonation threshold pressure. To examine the theoretical prediction,
 excised larynx experiments have been carried out for rhesus macaques
 (Macaca mulatta). Comparison of the larynges before and after surgical
 removal of the vocal membranes revealed that the phonation threshold
 pressure was indeed lower and, consequently, the vocal efficiency was
 higher in the presence of the vocal membranes. Irregular chaotic
 oscillations were also observed for some larynges with the vocal
 membranes. 
description: From two fresh cadavers of adult female macaques (#1, #2), the
 laryngeal samples were extracted, flash-frozen in liquid nitrogen, and
 stored at -80 degrees. The frozen samples were thawed shortly before the
 excised larynx experiments, which were performed under two conditions: (A)
 in the presence of the vocal membranes and (B) in the absence of the vocal
 membranes. Under both conditions, individual larynx was
 mounted on a vertical tracheal tube. The flow rate of humid air (about 37
 degrees; 100 % relative humidity) that comes from an air pump
 (SilentAirCompressor Sc820, Hitachi Koki Co., Ltd., Tokyo, Japan) was
 controlled by a pressure regulator (10202U, Fairchild, Winston-Salem, NC)
 and a digital mass flow controller (CMQ-V, Azbil, Santa Clara, CA). To
 induce vocal fold vibrations, the glottal air space was narrowed by
 manually adducting the arytenoid cartilages. Once the adjustment was made,
 positions of the arytenoid cartilages were fixed by a surgical suture.
 This configuration was used commonly for the two conditions (A) and
 (B). The dynamics of the vocal folds and the vocal membranes was monitored
 using a borescope with a view angle of 70 degrees (BAL-72718HT, Shodensha,
 Osaka, Japan) attached to a high-speed video camera (Fastcam Nova S6,
 Photron, Tokyo, Japan) (Sampling: 10000 FPS, Shutter speed: 1/25000 s).
 The acoustic sound and the sound pressure level (SPL) were measured by an
 omnidirectional microphone (Type 4192, Nexus conditioning amplifier, Bruel
 and Kjaer, Tokyo, Japan) and a sound level meter (Type 2250-A, Bruel and
 Kjaer), respectively, both located 15 cm from the larynx. The subglottal
 pressure was monitored using a pressure transducer (Differential pressure
 transducer, PDS 70GA, Kyowa, Osaka, Japan; Signal conditioner, CDV 700A,
 Kyowa), which was mounted flush on the inner wall of the tracheal tube, 2
 cm upstream of the excised larynx. All signals were stored into a digital
 recorder (Controller, PXIe-8840, National Instruments; Input/output card,
 BNC-2110, National Instruments; Software, Labview, National Instruments,
 Austin, TX, USA) with a sampling frequency of 12.5 kHz.
 To measure the phonation threshold pressure, the flow-rate was
 slowly increased from 0 l/min to a maximal value in 3 sec (the maximal
 airflow was set to be about 1.5 times of the onset airflow).
 Self-sustained oscillations of the larynx were continued to be measured
 for 4 sec. Then, the flow-rate was decreased to 0 l/min in 3
 sec. In the experimental condition (A), two oscillation
 patterns were observed:<br>(A1) the vocal folds did not show a
 strong vibration and only the vocal membranes oscillated, <br>(A2)
 both vocal folds and membranes oscillated simultaneously.<br>The
 pattern (A2) was observed when both upper and lower parts of the vocal
 folds were adducted. The pattern (A1) was observed when the lower parts of
 the vocal folds were abducted from the condition of observing the pattern
 (A2). A total of three oscillation patterns (A1), (A2),
 (B) were examined. For each oscillation pattern, the phonation threshold
 pressures were measured for 10 times.
description: # Vocal membranes lower the phonation threshold pressure in rhesus
 macaques (Macaca mulatta)
 [https://doi.org/10.5061/dryad.73n5tb356](https://doi.org/10.5061/dryad.73n5tb356) ## Description of the data and file structure The data is composed of 6 data sets, named as "macaque*_*.tar.gz". "macaque{1,2}_*.tar.gz" give the data recorded from macaques #1 and #2, respectively. "macaque*_vm.tar.gz" are for condition (A1), in which vocal folds did not show a strong vibration and only the vocal membranes oscillated. "macaque*_vmvf.tar.gz" are for condition (A2), in which both vocal folds and membranes oscillated simultaneously. "macaque*_vf.tar.gz" are for condition (B), in which vocal folds oscillated in the absence of vocal membranes. Each file (".tar.gz") includes 10 sets of microphone signals (physical unit: voltage) and subglottal pressure signals (physical unit: Pa) ("macaque*.csv"), microphone sounds ("macaque*.wav"), and high-speed filming data ("macaque*.mp4").