A major drawback of current speech technologies is the fact that when the system is prompting messages (outgoing) it is unable to listen. That is, speech recognition and speech prompting do not occur simultaneously. In most applications the caller has to wait for a system's instruction to be completed before speaking. Usually the users are instructed to ``please wait for the beep before speaking''.
Some technologies offer cut-through capabilities; these allow users to interrupt the system and anticipate on its messages. Speech recognition takes place even during the system prompts . This capability is highly appreciated by experienced users who may interrupt the system's outgoing speech any time. Moreover they may use a sequence of words instead of a single one. Of course it is necessary to carefully handle the dialogue structure in order to avoid interrupting the system because of noise or unexpected words.
This capability has to be distinguished from the so called voice stop where the system detects some speech activity (energy level), stops prompting its present message, and switches to the recognition mode expecting the user to say something. Usually the system instructs the user to say ``STOP'' whenever he is ready to input his choice and then wait for the beep before speaking. In that case the beep is still there and speech recognition does not occur simultaneously to the speech playback .
The application developer may use these capabilities or may not (when he wants the users to listen to a complete message for security reasons). So the technology provider should indicate whether this is optional, mandatory, or not implemented. The distinction may be defined as follows: