VOT is the abbreviation of Voice Onset Time, a phonetic term. The word "onset" means start. It refers to the length of time between the release of a consonant and the voicing of the following segment which is marked by vocal fold vibration.
VOT can be classified as positive, zero and negative. This classification is based on the start time of voicing relative to the release of a plosive. In English, all three occur because English has voiceless aspirated, voiceless unaspirated and voiced plosives.
The words "pie", "spy" and "buy" all have a bilabial plosive. In "pie" and "buy" it is word-initial and in "spy" it is the second segment of the word. Despite orthography, the nucleus in each word is the diphthong of "my" and "shy".
In the word "pie", the plosive is aspirated. This means that voicing occurs after the release of the voiceless aspirated bilabial plosive. In this word, the VOT is positive.
The word "spy" also has a voiceless bilabial plosive, but this one is unaspirated. In English, all plosives which follow a word-initial alveolar fricative are unaspirated. This is completely predictable. The voicing of the diphthong occurs at about the same time as the release of the voiceless unaspirated bilablial plosive. In this case, the VOT is zero.
With "buy", the voicing of the diphthong begins prior to the release of the voiced bilabial plosive. Note that in this case both segments are voiced. Because voicing begins prior to the release of the plosive, the VOT is negative.
It is important to note that voice onset times can vary considerably from one language to another. For example, voiced plosives are not as voiced in English as they are in languages such as French and Russian. In the English word "do", the plosive is not as voiced as in the French word "deux" (two). The result is that the French word has a more negative VOT than the English one.
To further illustrate, Dutch is unique among Germanic languages in its lack of voiceless aspirated plosives, but the voiceless unaspirated plosives are not identical to those of languages such as French. The Dutch word "peer" and the French word "poire", both meaning pear, consist of a voiceless unaspirated bilabial plosive. The VOT is zero. However, the voicing occurs earlier in French than it does in Dutch. Thus, a slight lag occurs in the release of Dutch voiceless plosives relative to voicing. The two languages share voiceless plosives, but their VOTs are a little different.
VOT, the common abbreviation of Voice Onset Time, is associated with phonetics. The study of VOT aids phoneticians in analyzing and classifying the length of time between the release of a consonant and the start of voicing of the following segment in the languages of the world.