MAS.632 Conversational Computer Systems - MIT OpenCourseWare

Inteaive Yoice Respoe
next set of lights" or warn when a one-way street becomes two way. To provide
adequate warning, each step of the directions is repeated twice: once about 30
seconds before the intersection in question and another just before the decision
point.
Precise timing of detailed utterances such as "Take a left at these lights"just as
the vehicle approaches the intersection, along with the use of deictic pronouns"O
help instill confidence in the driver. Because there is no display and Back Seat
Driver does not speak more often than is necessary, it is easy to doubt that it is
actually "alive." Utterances of this type affirm that the system is tracking the
vehicle's location correctly and will speak when necessary.
To speak at the right time Back Seat Driver needs to manage time in concert
with the real world of a vehicle in motion. Time management is achieved by maintaining
a series of goals with an estimated time to speak each goal. The time at
which an utterance must commence changes relative to the vehicle's speed, and
there may not be adequate time to speak all goals. The goals are prioritized so
that the most important are spoken first. A goal that would be interrupted by a
higher-priority goal (given an anticipated moment to speak the goal) will instead
choose not to start as it would be confusing for the system to interrupt itself as
well as waste valuable time. Knowing how long it will take to speak a goal
enables advance planning and allows some goals to be merged if there is not
enough time for each in isolation [Davis and Schmandt 1990]. For example, just
before a shortjog in the road, Back Seat Driver might say "Take the left at the end
of the road, and then you're going to take the very next right."
Goals are dynamic and can change during the course of the trip because the
driver does not always follow the directions correctly Back Seat Driver must cope
with these driver errors. It indicates the mistake ("Oops, I meant for you to take
a right.. .")but then adapts to the error by computing a new route after telling
the driver (". . .but that's OK, I'll figure out a new way to get there"). The Route
Finder can operate incrementally while the vehicle is in motion although the
driver is told "Slow down while I think about it." All the utterances were carefully
chosen during a long iterative design cycle; it is inappropriate to speak in a manner
that encourages the driver to simply slam on the brakes possibly causing an
accident.
The primary focus of Back Seat Driver has been to experiment with discourse
generation in real time so as to determine the appropriateness of speech output
for a computer driving assistant. The project was based on the belief that voice
could be employed effectively in a real-time application by implementing a goaloriented
discourse model. Although it was never rigorously tested against a display-based
system, many users who test-drove the car found it effective and even
reassuring. This was achieved in large part by the careful wording and timing of
each utterance to match the car's position and speed.
"'Deicticsare pronouns that refer to objects identified by their position relative to the
speaker. "'This"and "these"refer to nearby objects, "that"and "those" to distant objects.
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