MINISTERIO DE EDUCACIÓN

There are several factors that can affect vocal fold vibration and consequently VOT such as place of articulation, contact surface area of stops involved, and speech rate. In their study of VOT in Saudi Arabic, Flege & Port (1981:130) found that the place of articulation of the stop had an effect on VOT in Saudi Arabic. This is due to the speed of the articulators involved. Maddieson (1999:620) points out that the release movement of a velar /k/ is slower than that of an alveolar /t/ or bilabial /p/. The rotational movement of the jaws speeds the release movement of /t/ and /p/ in comparison with the back of the tongue for /k/ because the jaw pivot is closer to /k/. Any movement of the lower jaw will result in the lower lip moving further than the tongue during the same period of time. The oral opening through which air escapes during the release phase increases in size at a slower rate for /k/. As a result, more time is needed to reach the required transglottal pressure for voicing to be initiated.

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Therefore the closer the articulators are to the jaw pivot, the longer the delay in vocal fold vibration and therefore longer VOT.

Another factor that contributes to VOT variations in different stops is the extent of contact between the articulators involved. Cho & Ladefoged (1999:326) state that the area of contact of a velar /k/ covers a larger surface area than that of bilabial and alveolar stops and that stops with a large surface area of contact have a longer VOT. This is further explained by Stevens (1999). The rate of change in intra oral pressure after the release depends on the rate of increase in the cross-sectional area at the constriction. A velar stop closure has a large surface area of contact and as a result a Bernoulli force acting on the articulators is larger. This results in a slow change in the cross-sectional area of the articulators in comparison with alveolar stops where a small Bernoulli effect acts on the articulators. Therefore there is a rapid decrease in intra oral pressure following the release of an alveolar stop but a gradual decrease for the velar stop. As a result, VOT is longer for velar stops than for alveolar stops (Stevens 1999:326).

In their study of the VOT of speakers from 18 languages, Cho & Ladefoged (1999) also state that VOT may vary with place of articulation and that there is a longer VOT when the closure is further back and there is a more extended contact area. They argue that due to the small cavity behind a velar closure there is a smaller volume of air than behind this closure than in the case of an alveolar closure. This also results in higher pressure behind the velar closure at the point of release of the closure. As a result, it will take a longer time for the pressure behind the closure to drop in order to reach the appropriate transglottal pressure required for initiating vibration vocal fold and therefore longer VOT.

Furthermore, an increase in the speed of the articulators involved results in the decrease of VOT (Cho & Ladefoged 1999). A faster articulatory velocity (e.g., the movement of the lower lip as compared to the tongue dorsum) allows a more rapid decrease in the pressure behind the closure and thus a shorter time is needed before building up an appropriate transglottal pressure. In their study of the effect of speaking

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rate on VOT, Kessinger & Blumstein (1998:125) found that changes in speech rate had an effect on VOT durations observing that as speaking rate slows in voiceless stops, there was an increase in both VOT and vowel durations.

The above applies to stop consonants occurring as singletons in SI or SF position. However, due to coarticulation, in which individual segments influence each other in connected speech, it is common that the voicing of a stop is also affected by the voicing of an adjacent stop in a sequence as a result of voice assimilation. In SI and SF stop clusters, in addition to across word boundary stop sequences, a voiced C1 may be devoiced as a result of a neighbouring voiceless C2 or a voiced C2 may become devoiced as a result of a voiceless C1. Some languages exhibit consonant clusters that only agree in voicing. These types of clusters are known as harmonic clusters because the laryngeal quality is consistent throughout the cluster (Chitoran 1998:121). One of the languages exhibiting this phenomenon is Georgian, in which the two consonants of a SI or SF cluster are both voiced, both aspirated, or both ejective. This is not the case in TLA where stop clusters in SI, SF, or across word boundaries can either agree or disagree in terms of voicing as in /dkar/ ‗male‟, /wagt/ ‗time‟, and /ʃad#tal/ ‗held a wire‟. It is anticipated that this will result in voice assimilation across the word boundary which will be further discussed in section 2.3.2.1. As will become apparent, across a word boundary two-stop sequences C#C can consist of stops disagreeing in their voicing as in /ʃid#kif/ ‗catch a slap‟.