What is the difference between peripheral and non-peripheral vowels?

Question:

What is the difference between peripheral and non-peripheral vowels?

Any phonetician here? I study at university (in Czech Republic) English Philology (and History...doesnⴴ matter now, does it :-)) and my 'most favourite' lecture is Phonetics and Phonology and this is a question I canⴴ find an answer for! Help, please...

Best Answer - Chosen by Asker:

The idea that vowel nuclei in many northern European languages can be divided into peripheral and non-peripheral categories is discussed. Peripheral vowels are those located at the edge of the vowel envelope, and non-peripheral nuclei are those located on the inside. This assertion has not received as much scrutiny as it should. There are at least five questions that could be raised about it: (1) Do the diachronic trends always hold true? (2) Can peripheral and non-peripheral nuclei always be distinguished? (3) When a shift occurs, is peripherality the cause and the shift the effect, or vice versa? (4) Do monophthongs and diphthongs really behave in the same ways? (5) What is the phonetic motivation for the observed raising of peripheral nuclei and lowering of non-peripheral nuclei? Three overriding points are made. First, the evidence suggests that peripherality is not a cause of vowel shifts as much as a product of them. Second, contrasts such as tense/lax contrast should be viewed holistically, taking all three correlates together. Third, researchers should continue looking for phonetic motivations for sound changes.