6 - Downtrends

Summary

Introduction

Utterances tend to fall in fundamental frequency, a phenomenon known as ‘declination’. The explanation has been sought in falling subglottal pressure (Lieberman 1967; Collier 1975b). After expanding his lungs to take in breath, the speaker will slowly ease up on the tension of the muscles he used for the breath intake (probably the diaphragm, with or without the aid of his chest muscles), so as to slow down the elastic recoil of the lungs and thereby prolong the period of positive pressure below the larynx which is needed for the production of a fluent portion of speech. Unless the speaker uses his muscles to force out the remaining air from his lungs during this slowed down exhalation phase, the pressure below the larynx will drop. Since lower subglottal pressure will lead to slower vocal fold vibration rates, F₀ declination will result.

As with the F₀ dependence on larynx size and articulatory precision discussed in the previous chapter, the effect has a physiological explanation, but many instantiations of the phenomenon are likely be under the control of the speaker (cf. 't Hart, Collier, and Cohen 1990: 136). The number of times that portions of speech bounded by air intakes, termed ‘breath groups’ by Lieberman (1967), coincide with intonational phrases is low, though much better than chance. In a study on Dutch, Appels (1985) found that 30 out of 70 ι-breaks coincided with the audible intake of air.