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In summary, the most salient acoustic correlate to Mono implosives concerns the
signal amplitude during the closure period. Specifically, Mono implosives exhibit either
an increase in signal amplitude during the latter part of oral closure or the maintenance of
a large, level signal amplitude. In addition, a biphasic pattern indicative of
laryngealization is observed in most of the tokens having a large, level amplitude, and a
small number of tokens exhibit voicelessness during the initial part of the closure period.
8.1.3 Labial-velars
There are several articulatory gestures which may be manifest in labial-velar stops
and may distinguish them from other types of stops. I will examine the acoustic evidence
for these in Mono. First, in some languages labial-velar stops employ a complex
airstream mechanism. Second, in many languages there is evidence that the labial and
velar gestures are staggered, with the velar gesture slightly in advance of the labial one.
Third, it has been claimed that the voice onset time (VOT) of labial-velar segments is
shorter than for labial and velar segments.
First, I address the issue of airstream mechanism. As pointed out in Chapter 2,
Kamanda (1998) classifies labial-velar stops as implosives in Mono. I offered typological
evidence in that chapter as to why that characterization is not appropriate. In this chapter,
I offer acoustic evidence for their classification as plain stops rather than implosive stops.
Ladefoged (1968) studied the airstream mechanism of labial-velar stops in 33
African languages. He found that the majority of the languages (23) had both pulmonic
egressive and velaric ingressive airstreams. The dorsum slides back in the articulation of
the sound, and as a result air flows into the oral cavity at both ends. The velaric
ingressive airstream gives an auditory impression of suction at release, which could give
the impression of an implosive sound.
In addition, Ladefoged found that eight languages had labial-velar stops which
involved three airstream mechanisms: a pulmonic egressive mechanism followed by a
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