Linguistic Style Improvisationfor Lifelike ComputerCharacters
Marilyn A. Walker
AT&TResearch Laboratories
600 Mountain Ave.
Murray Hill, NJ 07974
walker @ research.att.com
Janet E. Cahn
MIT Media Lab
20 Ames St.
Cambridge,
MA 02139
cahn @ media.mit.edu
Just because you are a character doesn’t mean that
you have character. (Wolfto Raquelin PulpFiction, Q.
Tarantino)
(Laszloand Ilsa enter Rick’sCafe)
Headwaiter:Yes, M’sieur?
Laszlo:I reserveda table. VictorLaszlo.
Waiter:Yes,M’sieurLaszlo.Rightthis way.
(LaszloandIlsa followthe waiterto a table)
Laszlo:Twocointreaux,please.
Waiter:Yes,M’sieur.
Laszlo:(to Ilsa) I sawnooneof Ugarte’sdescription.
Ilsa: Victor,I feel somehow
weshouldn’tstay here.
Abstract
This paper introduces Linguistic Style Improvisation,
a theory and algorithms for improvisation of spoken
utterances by artificial agents, with applications to interactive story and dialogue systems. Weargue that linguistic style is a key aspect of character, and showhow
speech act representations commonin AI can provide
abstract representations from which computercharacters can improvise’. Weshow that the mechanisms
proposedintroduce the possibility of socially oriented
agents, meetthe requirementsthat lifelike characters be
believable, and satisfy particular criteria for improvisation proposed by Hayes-Roth.
1
Stephen J. Whittaker
AT&TResearch Laboratories
*
600 Mountain Ave.
Murray Hill, NJ 07974
whittaker @research.att, com
Figure 1: Excerpt from the Casablancascript.
Introduction
Recent workon interactive dramasystems attempts to create
virtual environmentsfor learning or entertainment in which
humansand lifelike computercharacters engage in interesting and emotionally evocative play [Loyall and Bates,
1995, Rich et al., 1994, Maeset al., 1994]. Previous work
suggests that the key requirements for these characters include believability, the ability to represent and expressemotion, and the ability to respondto humanusers in an interpretable way. In addition, it is desirable for a character to
be able to IMPROVISE
on an abstract specification of an act
that it intends to perform,either by its ownvolition or under
the direction of another agent [Hayes-Rothand Brownston,
1994, Hayes-Rothet al., 1995]. Here, we argue that linguistic style is a key aspect of character, previouslyignored,
and present a theory of, and algorithmsfor, Linguistic Style
Improvisation by computercharacters.
Linguistic Style Improvisation (henceforth LSI) concerns
the choices a speaker makesabout the SEMANTIC
CONTENT,
SYNTACTIC
FORM
and ACOUSTICAL
REALIZATION
of their spoken utterances. As an exampleof howlinguistic style can
*Thisresearch wassupportedin part by HewlettPackardLaboratories U.K., by the Universityof Pennsylvania,by Mitsubishi
Electric ResearchLaboratories,by the MITMediaLaboratory,and
by AT’FResearchLaboratories.
61
conveycharacter, consider Laszlo’s request for two cointreaux in 1, from the Casablancascreenplay in Figure 1. In
the film, this requestis deliveredin pleasant tones.
(1) a. Twocointreaux, please.
Weshowhowit is possible, given an abstract plan-based
representation of Laszlo’s utterance as a speechact, to automatically improviseany of the alternative stylistic realizations in 2 for requesting two cointreaux:
(2) a. Bring us two cointreaux, right away.
b. Youmust bring us two cointreaux.
c. Wedon’t have two cointreaux, yet.
d. Youwouldn’t want to bring us two cointreaux, would
you?
Clearly, speakers makesuch stylistic choices whenthey realize their communicative
intentions, and these stylistic realizations express the speaker’scharacter and personality. Furthermore, listeners drawinferences about the character and
the personality of a speaker based on the speaker’s choices.
Accordingto theories of social interaction a speaker’schoice
is controlled by social and affective variables [Goffman,
1983, Brownand Levinson, 1987]. For example, thepower
variable can affect Laszlo’s choice amongthe forms in 2; if
he believes he is morepowerful than the waiter he maysay
2a or 2b; but if he believes he is less powerfulhe maysay
2d.
Our work on Linguistic Style Improvisation is most similar to Hayes-Roth’sworkon directed improvisation [HayesRoth and Brownston,1994, Hayes-Rothet al., 1995]. In her
work, directions to computercharacters are abstract representations of acts that the characters can improviseon and