The whole body plethysmograph in speech research

The whole body plethysmograph is used to monitor a subject’s pulmonic activity and consists of an air‐tight box just big enough to contain the subject. The subject breathes and speaks through a tube or facemask which vents to the atmosphere. Changes in thoracic or abdominal volume during breathing cause proportional changes in the volume of the air inside the box. Either an air pressure or an air flow transducer may be mounted in a second vent in the wall of the box in order to measure the aerodynamic variations associated with respiration including those in the expiratory phase on which virtually all voice production is superimposed. The device, which can be constructed fairly simply, is as accurate as the transducer used. If the breathing vent is momentarily closed off, leaving the subject to breathe the air inside the box—which now constitutes a closed system as regards exchange of air between speaker and box—a rough measure of subglottal air pressure may be obtained in a noninvasive way. Its use in phonetic research will be demonstrated by means of a 10‐min video.