Isochrony

Isochrony is the postulated rhythmic division of time into equal portions by a language. Rhythm is an aspect of prosody, others being intonation, stress and tempo of speech. Isochrony is the postulated rhythmic division of time into equal portions by a language. Rhythm is an aspect of prosody, others being intonation, stress and tempo of speech. Three alternative ways in which a language can divide time are postulated: The idea was first expressed thusly by Kenneth L. Pike in 1945, though the concept of language naturally occurring in chronologically and rhythmically equal measures is found at least as early as 1775 (in Prosodia Rationalis). This has implications for linguistic typology: D. Abercrombie claimed 'As far as is known, every language in the world is spoken with one kind of rhythm or with the other ... French, Telugu and Yoruba ... are syllable-timed languages, ... English, Russian and Arabic ... are stress-timed languages.'While many linguists find the idea of different rhythm types appealing, empirical studies have not been able to find acoustic correlates of the postulated types, calling into question the validity of these types. However, when viewed as a matter of degree, relative differences in the variability of syllable duration across languages have been found. In a syllable-timed language, every syllable is perceived as taking up roughly the same amount of time, though the absolute length of time depends on the prosody. Syllable-timed languages tend to give syllables approximately equal prominence and generally lack reduced vowels. French, Italian, Spanish, Brazilian Portuguese, Icelandic, Cantonese, Mandarin Chinese, Georgian, Romanian, Armenian, and Turkish are commonly quoted as examples of syllable-timed languages. This type of rhythm was originally metaphorically referred to as 'machine-gun rhythm' because each underlying rhythmical unit is of the same duration, similar to the transient bullet noise of a machine-gun. Since the 1950s, speech scientists have tried to show the existence of equal syllable durations in the acoustic speech signal without success. More recent research claims that the duration of consonantal and vocalic intervals is responsible for syllable-timed perception. Some languages such as Japanese, Gilbertese, Slovak or Ganda also have regular pacing but are mora-timed rather than syllable-timed. In Japanese, a V or CV syllable takes up one timing unit. Japanese does not have vowel length or diphthongs but double vowels, so CVV takes twice the time as CV. A final /N/ also takes as much time as a CV syllable and, at least in poetry, so does the extra length of a geminate consonant. However, colloquial language is less settled than poetic language, and the rhythm may vary from one region to another or with time. Ancient Greek and Vedic Sanskrit were also strictly mora-timed. Proto-Indo-European probably was as well. In a stress-timed language, syllables may last different amounts of time, but there is perceived to be a fairly constant amount of time (on average) between consecutive stressed syllables. Consequently, unstressed syllables between stressed syllables tend to be compressed to fit into the time interval: if two stressed syllables are separated by a single unstressed syllable, as in delicious tea, the unstressed syllable will be relatively long, while if a larger number of unstressed syllables intervenes, as in tolerable tea, the unstressed syllables will be shorter.