VOICE ONSET TIME (VOT)
The term Voice Onset Time (VOT) refers to the timing of the beginning of vocal cord vibration in CV sequences (i.e., CV syllables) relative to the timing of the consonant release. The theory proposes that this timing is critical for accurate perception of the voiced/voiceless phonological contrast between consonants. This holds for stop consonants and to some extent for fricative consonants (that is, when the consonant is a plosive and often when the consonant is a fricative).
In phonology, consonants are contrasted and differentiated on the [voice] feature. Thus /b, d, g/ are marked [+voice] and /p, t, k/ are marked [–voice] in phonology. The abstract nature of phonology implies firm boundaries to the segment, and a straightforward conversion from abstract to concrete (phonemic representation to phonetic representation) as phonetics realizes phonology. In fact, it can be shown that in English and many other languages, vocal cord vibration does not occur throughout a [+voice] stop, and that it does not begin simultaneously with the beginning of the vowel following a [–voice] stop.
VOT may be negative, zero or positive. Zero VOT indicates that vocal cord vibration has begun simultaneously with the release of the plosive consonant; negative VOT indicates vibration beginning earlier than the release of the plosive consonant; and, positive VOT indicates vibration beginning after the release. Different languages have different methods of phonetic realization of this phonological feature. Notice that zero VOT in French cues the perception of a [–voice] stop, whereas in English the same auditory cue indicates a [+voice] stop.
Experiments with VOT have shown that abstract phonological specifications like [+voice] or [–voice] do not always have a direct one-to-one phonetic realization. Phonetic features (in this case that of vocal cord vibration) do not necessarily correspond directly with phonological features (in this case [voice]), nor do phonetic features necessarily reflect the abstract segmental divisions of phonology, but tend to 'blur' very often across where a segmental boundary might be. Notice also that different languages often realize the same abstract phonological specifications (i.e., phonemic representations) differently in their phonetics (i.e., phonetic representations). Here the phonological feature [+voice] is realized in English by a zero VOT, but in French by a comparatively long negative VOT, whereas the [–voice] feature was realized in English by a long positive VOT, but in French by a zero or very short positive VOT.
