A Comparison of /s/ and /z/ for an English Speaker

An experiment in which oral pressure and volume flow of air through the mouth were measured simultaneously for one speaker of English has shown that: (1) the timing of the tongue movements for /s/ and /z/ is the same when similar phonetic contexts are compared; (2) air flow and pressure are both significantly greater for /s/ than for /z/, in agreement with previous work; but (3) aerodynamic measures indicating the degree of tongue occlusion show no significant difference between /s/ and /z/. The feature tense-lax operates in the expected way at the acoustic stage for /s/ and /z/, but applies, at the articulatory stage, either not at all, or else in the opposite direction to that expected. Experiments with the same speaker, including oesophageal pressure measurements to indicate tracheal pressure, support the view that the only significant difference in the articulation of these /s/ and /z/ segments lies in the glottal adjustment and not in muscular effort defined in any other way, nor in breath force. The observed acoustic effects follow automatically from the different oral pressures and air flows, which are the direct result of the different glottal articulations.