Explosives, implosives, and nonexplosives: the linguistic function of air pressure differences in stops

Nonexplosive stops, including implosives and other stops regularly lacking an explosive release burst, occur in roughly 20% of the world's languages, yet their phonological and phonetic properties are still poorly understood. This paper seeks to determine the phonological feature that characterizes this class of sounds. The classical definition of implosives in terms of the ingressive glottalic airstream mechanism raises a number of problems and does not generalize to other types of nonexplosives. It is proposed here instead that the feature underlying the class of nonexplosive stops as a whole is nonobstruence, defined as the absence of positive oral air pressure during occlusion. This definition is shown to extend to a previously undocumented type of nonexplosive stop found in Ikwere, a Niger-Congo language spoken in Nigeria. In this language, the phonemically contrastive nonexplosive bilabial stops, though resembling implosives in certain respects, are produced with no lowering of the larynx, nor in the case of the voiced stop, any implosion at release. A study of the acoustic, articulatory and aerodynamic properties of these sounds shows that they satisfy the definition of nonobstruent stops. It is finally suggested that apparently contradictory aspects of the phonological patterning of nonexplosive stops across languages can be explained if they are viewed as both nonobstruents and nonsonorants. In this view, phonological feature theory requires both articulatory features such as [±obstruent] and acoustic features such as [±sonorant]