Luís Gustavo Martins recently completed his PhD thesis titled A computational Framework for Sound Segregation in Music Signals.
From the abstract: "[...] This dissertation proposes a ﬂexible and extensible Computational Auditory Scene Analysis framework for modeling perceptual grouping in music listening. The goal of the proposed framework is to partition a monaural acoustical mixture into a perceptually motivated topological description of the sound scene (similar to the way a naive listener would perceive it) instead of attempting to accurately separate the mixture into its original and physical sources. [...]"
Luis is probably best known in the MIR community for his contributions to Marsyas (the awesome open source software framework for audio processing with specific emphasis on MIR applications).
If you know of any other dissertations missing in the list of MIR PhDs please let me know.