The Internal Structure of Nasal-Stop Sequences: Evidence from Austronesian

The phonological and phonetic structure of nasal-stop sequences has elicited much attention. Yet, less is known about the internal timing of nasal-stop sequences than often assumed. This includes clusters, both nasal voiced-stop clusters (ND) and nasal voiceless-stop clusters (NT); and unary cases, most commonly prenasalized stops (ND) but also so-called postploded nasals (ND ).1 The latter are cases that have been described as being in some sense the mirror image of prenasalized stops, where the segment is taken to be primarily nasal, but with an oral release. (Nasal-stop sequence, or NC sequence, is used here to refer to both unary and cluster cases.)

Based on impressionistic phonological descriptions, we would expect the phonetic timing relationships schematized in Figure 1. First, in terms of overall duration, prenasalized stops (a) and postploded nasals (b) are expected to have roughly the overall duration of a single segment and nasal-stop clusters (c & d) should be longer, in line with the duration of other clusters in the language (Riehl 2008). In terms of relative duration of the nasal and oral components, in the case of prenasalized stops (a), the nasal component is expected to be quite brief, taking up just the beginning of the total duration. While in the case of postploded nasals (b), the converse is expected, with the nasal closure taking up the majority of the total duration and only a brief period of oral closure. In the case of nasal voiced-stop and nasal voiceless-stop clusters (c & d), the total duration is expected to be roughly evenly divided between the nasal component and oral component for both cases.

Phonetic data addressing the realization of these phonological types is quite limited, but the available data suggest quite different realizations than expected. In a cross-linguistic study of nasals and nasalization in English, French, and Sundanese, Cohn (1990) observed a systematic asymmetry in the relative timing of the nasal and oral portions in nasal voiceless-stop vs. nasal voiced-stop clusters: For the NT cases, the nasal and oral components each take up about half of the total duration, as expected; while in the ND cases, the sequence is nasal for all but a very brief period. While others have since noted a similar asymmetry, no full account has been offered. As far as unary cases, claims have been made about there being different types based on relative timing of the nasal and oral portions. First, do the prenasalized stops exhibit the expected pattern? Second, in the case of postploded nasals, are they indeed the mirror image of prenasalized stops? Are they actually unary segments or clusters? Finally are they a phonologically distinct type of NC sequence? The goal of this paper is to bring to bear a more extensive body of phonetic data in order to better understand the phonological structure and phonetic realization of this range of nasal-stop sequences. We present data from six Austronesian languages to investigate these questions. The Austronesian language family is known for its rich array of nasal-stop sequences, including nasal-obstruent clusters and cases of both prenasalized stops and what have been described as postploded nasals

In §2, we present some background on the question of prenasalized stops vs. nasal-stop clusters, reviewing relevant results from Riehl (2008) and in §3, the methodology of the present study. In §4, we investigate the asymmetry between the voiced and voiceless NCs and in §5 & §6, we consider the phonological status and phonetic realization of postploded nasals. We will see that to address each of these points the central issue is timing. This includes total duration, the relative timing of the nasal and oral components, and finally what we call microtiming, that is, the structure of the transition from nasal to oral and the nature of the oral component.