Spoken language interfaces based on interactive semantic language models [16, 14] allow probabilities for hypothesized words to be conditioned on the semantic interpretation of these words in the context of some interfaced application environment. This conditioning may allow users to avoid recognition errors in an intuitive way, by adding extra, possibly redundant description. This paper evaluates the effect on error reduction of redundant descriptions in an interactive semantic language model. In order to evaluate the effect in natural use, the model is run on rich domains, supporting references to sets of individuals (instead of just individuals themselves) arranged in multiple continuous dimensions (a 2-D floorplan scene). Results of these experiments suggest that an interactive semantic language model allows users to achieve significantly higher recognition accuracy by providing additional redundant spoken description.