Levels of reduction for German tense vowels

In natural speech there are differences in the realisation of vowels. Numerous factors such as speaking style, prosody, or word class can cause vowel reductions. It is investigated whether vowel reductions can be described using discrete levels and, if yes, how many levels can be reliably perceived. The reduction of a vowel was judged by matching stimuli to representatives of reduction levels (prototypes). The results were investigated on the basis of inter-subject agreement. The resulting prototypes were evaluated by further perception experiments as well as artificial neural networks. The transferability of the reduction levels to other speakers was also investigated. The experiments show that listeners can reliably discriminate 3 to 5 reduction levels depending on the vowel. They use the prototypes speaker-independently, while neural networks trained with the material from one speaker are not applicable to other speakers. Lastly, the relationships between reduction levels and prosodic factors (lexical word stress, pitch accent, prominence) as well as word class (content words vs. function words) were investigated.