26. The method of claim 20 wherein the acoustic models are characterized by a plurality of parameters, each node representing a set containing one or more of the parameters.
20. A method for use in an apparatus for recognizing selected speech based on acoustic models, the method comprising: modifying the acoustic models in response to selected data representing a sample of the selected speech; and defining a hierarchical structure which includes a plurality of levels, each level having one or more nodes thereon, each level in the structure arranged higher than every other level having a smaller number of nodes thereon than the other level, each node being associated with a probability measure which is determined based on at least the selected data, each node on each level having two or more nodes thereon being connected to a node on a second level higher than the level having two or more nodes thereon, the probability measure associated with each node on each level having two or more nodes thereon being a function of at least the probability measure associated with the node connected thereto on the second level, the acoustic models being modified based on at least the probability measure associated with each node on a selected level.