Linguistic Style Improvisation for Lifelike Computer Characters AAAI 96 Workshop on AI, Alife and Entertainment, Portland Marilyn A. Walker Janet E. Cahn Stephen J. Whittaker AT&T Research Laboratories MIT Media Lab AT&T Research Laboratories 600 Mountain Ave. 20 Ames St. 600 Mountain Ave. Murray Hill, NJ 07974 Cambridge, MA 02139 Murray Hill, NJ 07974 walker@research.att.com cahn@media.mit.edu whittaker@research.att.com Just because you are a character doesn’t mean that you have character. (Wolf to Raquel in Pulp Fiction, Q. Tarantino) Abstract This paper introduces Linguistic Style Improvisation, a theory and algorithms for improvisation of spoken utterances by artificial agents, with applications to in- teractive story and dialogue systems. We argue that lin- guistic style is a key aspect of character, and show how speech act representations common in AI can provide abstract representations from which computer charac- ters can improvise. We show that the mechanisms proposed introduce the possibility of socially oriented agents, meet the requirements that lifelike characters be believable, and satisfy particular criteria for improvisa- tion proposed by Hayes-Roth. 1 Introduction Recent work on interactive drama systems attempts to create virtual environments for learning or entertainment in which humans and lifelike computer characters engage in inter- esting and emotionally evocative play [Loyall and Bates, 1995, Rich et al., 1994, Maes et al., 1994]. Previous work suggests that the key requirements for these characters in- clude believability, the ability to represent and express emo- tion, and the ability to respond to human users in an inter- pretable 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 own volition or under the direction of another agent [Hayes-Roth and Brownston, 1994, Hayes-Roth et al., 1995]. Here, we argue that lin- guistic style is a key aspect of character, previously ignored, and present a theory of, and algorithms for, Linguistic Style Improvisation by computer characters. Linguistic Style Improvisation (henceforth LSI) concerns the choices a speaker makes about the SEMANTIC CONTENT, SYNTACTIC FORM and ACOUSTICALREALIZATION of their spo- ken utterances. As an example of how linguistic style can This research was supported in part by Hewlett Packard Lab- oratories U.K., by the University of Pennsylvania, by Mitsubishi Electric Research Laboratories, by the MIT Media Laboratory, and by ATT Research Laboratories . (Laszlo and Ilsa enter Rick’s Cafe) Headwaiter: Yes, M’sieur? Laszlo: I reserved a table. Victor Laszlo. Waiter: Yes, M’sieur Laszlo. Rightthis way. (Laszlo and Ilsa follow the waiter to a table) Laszlo: Two cointreaux, please. Waiter: Yes, M’sieur. Laszlo: (to Ilsa) I saw no one of Ugarte’s description. Ilsa: Victor, I feel somehow we shouldn’t stay here. Figure 1: Excerpt from the Casablanca script. convey character, consider Laszlo’s request for two coin- treaux in 1, from the Casablanca screenplay in Figure 1. In the film, this request is delivered in pleasant tones. (1) a. Two cointreaux, please. We show how it is possible, given an abstract plan-based representation of Laszlo’s utterance as a speech act, to au- tomatically improvise any of the alternative stylistic realiza- tions in 2 for requesting two cointreaux: (2) a. Bring us two cointreaux, right away. b. You must bring us two cointreaux. c. We don’t have two cointreaux, yet. d. You wouldn’t want to bring us two cointreaux, would you? Clearly, speakersmake such stylistic choices when they re- alize their communicative intentions, and these stylistic real- izations express the speaker’s character and personality. Fur- thermore, listeners draw inferences about the character and the personality of a speaker based on the speaker’s choices. According to theories of social interaction a speaker’s choice is controlled by social and affective variables [Goffman, 1983, Brown and Levinson, 1987]. For example, the power variable can affect Laszlo’s choice among the forms in 2; if he believes he is more powerful than the waiter he may say 2a or 2b; but if he believes he is less powerful he may say 2d. Our work on Linguistic Style Improvisation is most simi- lar to Hayes-Roth’s work on directed improvisation [Hayes- Roth and Brownston, 1994, Hayes-Roth et al., 1995]. In her work, directions to computer characters are abstract repre- sentations of acts that the characters can improvise on and