More recent work has investigated other types of reranking models, such as hierarchical syntactic language models (Bangalore and Rambow 2000), discriminative models trained to replicate user ratings of utterance quality (Walker, Rambow, and Rogati 2002), or language models trained on speaker-specific corpora to model linguistic alignment (Isard, Brockmann, and Oberlander 2006).
a major drawback of the utterancelevel overgenerate and rank approach is its inherent computational cost.