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languages on one hand (Degema and three Eastern Ijo languages), and the Chadic
language Hausa, on the other. The Niger-Congo languages she studied exhibit certain
regular acoustic patterns. First, the signal amplitude of the implosives either increases
gradually during the oral closure period or it is level and sizeable throughout the closure,
whereas plosives exhibit a gradual decrease in signal amplitude during closure. Second,
the implosive sound waves include high frequency energy during the first part of the
closure. She interprets this as a period of laryngealization (i.e. creaky voice), which is
then followed by modal phonation.
In Hausa, there is considerable variation in the production of implosives. One of
Lindau’s subjects produced implosives like those of the Niger-Congo speakers, five
subjects produced a voiceless beginning of the closure, and eight subjects produced
implosives with aperiodic vibrations throughout the closure. Ladefoged & Maddieson
(1996: 85) refer to these latter sounds as “creaky voiced implosives”.
Lindau’s characterization of laryngealization as aperiodic vocal cord vibrations
resulting in high frequency spectral energy is peculiar. Ladefoged & Maddieson (1996)
consider laryngealization to be periodic and note two possible articulations. The parts of
the vocal cords near the arytenoid may be held tightly so that only the ligamental parts
vibrate, or alternatively the ligamental and arytenoid parts vibrate separately and out of
phase with each other. This second articulation leads to an apparent doubling of the
glottal pulse rate. Ladefoged (1968: 16) notes that laryngealization sometimes but not
always occurs in implosive consonants. I examined Mono implosives to determine if
there was evidence for either high frequency energy or a biphasic pattern.
I examined 25 tokens of Mono implosives. Among these, 15 exhibited a rising
signal amplitude during the period of closure, whereas ten exhibited a large, level signal
amplitude. There was some evidence for the type of laryngealization described by
Ladefoged & Maddieson, as discussed below. In addition, a small number of tokens
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