22. A computer-implemented method of controlling a vehicle, comprising: receiving one or more instructions issued as speech; analyzing the speech using speech recognition software to provide a sequence of words and a word confidence measure for each word so recognized; analyzing the sequence of words to identify a semantic concept corresponding to an instruction based on the analysis, and a semantic confidence level for the identified semantic concept derived at least in part with reference to the word confidence measures of the words associated with the semantic concept; providing a spoken confirmation of the semantic concept so identified based on the semantic confidence level, the spoken confirmation having one of a speaking rate or a pitch adjusted according to an indicated response length; and using the semantic concept so identified to provide a control input for the vehicle; wherein the step of providing the spoken confirmation of the semantic concept comprises indicating that the instruction was not understood when the semantic confidence level is below a threshold, or the step of using the semantic concept comprises providing the control input for the vehicle when the semantic confidence level exceeds the threshold.
22. A computer-implemented method of controlling a vehicle, comprising: receiving one or more instructions issued as speech; analyzing the speech using speech recognition software to provide a sequence of words and a word confidence measure for each word so recognized; analyzing the sequence of words to identify a semantic concept corresponding to an instruction based on the analysis, and a semantic confidence level for the identified semantic concept derived at least in part with reference to the word confidence measures of the words associated with the semantic concept; providing a spoken confirmation of the semantic concept so identified based on the semantic confidence level, the spoken confirmation having one of a speaking rate or a pitch adjusted according to an indicated response length; and using the semantic concept so identified to provide a control input for the vehicle; wherein the step of providing the spoken confirmation of the semantic concept comprises indicating that the instruction was not understood when the semantic confidence level is below a threshold, or the step of using the semantic concept comprises providing the control input for the vehicle when the semantic confidence level exceeds the threshold. 23. The method of claim 22 , wherein the step of analyzing the speech to provide a sequence of words comprises using continuous hidden Markov models.