Phonetic and phonological nature of prosodic boundaries: evidence from Modern Greek
Research on prosodic structure, the underlying structure organising the prosodic grouping of spoken utterances, has shown that it consists of hierarchically organised prosodic constituents. The present thesis explores the nature of this constituency, in particular the question of whether prosodic structure is comprised of a given set of qualitatively distinct domains, or of a set of domains of the same type varying only gradiently in "strength", or a possible mixture of both types of relations across prosodic levels. This question is addressed by testing how prosodic constituency (mirrored on boundary strength manipulations) is signalled acoustically via pre- and post-boundary durations, intonation contours, and two sandhi processes, namely vowel hiatus resolution and post-nasal stop voicing in Modern Greek. Results show that the phonetic signalling of boundary strength provides support for a mixture of both differences of type and strength across prosodic levels, with some levels only differing in terms of their strength. Pre-boundary durations and resolution of vowel hiatus are gradiently affected by boundary strength with shorter to longer durations from lower to higher domains, and less instances of vowel deletion higher in the hierarchy. Post-nasal stop voicing is qualitatively affected by boundary strength with almost all voicing instances occurring in the lowest constituent of the structure in the way a qualitative view of prosodic constituency would predict, and in line with research on prosodic phonology. Finally, both the alignment and scaling of intonation contours at the edges of domains is found to distinguish qualitatively the lowest domain from the higher ones. All higher phrasal domains align with respect to the boundary and their peak scaling varies consistently gradiently across speakers. When combining those two findings, support is provided for the existence of differences of strength and type within the same process. Taken together the results from these four phenomena support the postulation of an underlying prosodic structure with a limited number of qualitatively distinct domains, within which at the same time some type of recursivity or structured variability must be allowed for. It is shown that there are structural properties of speech, like the length of the utterance, influencing the organisation of utterances in a principled gradient manner, supporting the existence of differences of strength within domain types. These findings bear significance for theories of prosodic structure that have assumed either the view of solely qualitative differences, or sole boundary strength differences, as well as for future proposals on prosodic constituency. Finally, the use of Modern Greek in this thesis adds to the existing literature on a language that has been extensively used by researchers working in views supporting the existence of qualitative distinctions of type across prosodic domains, and provides the first in depth experimental analysis of post-nasal stop voicing.