Learning Automata based Approach to Model Dialogue Strategy in Spoken Dialogue System: A Performance Evaluation G.Kumaravelan Pondicherry University, Karaikal Centre, Karaikal. R. SivaKumar AVVM Sri Pushpam College, Thanjavur.

Dialogue System A system to provide interface between the user and a computer-based application Interact on turn-by-turn basis Dialogue manager  Control the flow of the dialogue information gathering from user communicating with external application communicating information back to the user  Three types of dialogue system (On initiativeness) finite state- (or graph-) based frame-based agent-based

Spoken Dialogue System Architecture Speech Recognition Dialogue Manager Back end Language Generation Text to Speech Synthesis Audio Spoken Language Understanding Words Semantic representation Concepts Words Audio

Properties of RL: The Agent-Environment Interaction

Cont… Immediate reward Long term reward Aim is to find the policy that leads to the highest total reward over T time steps (finite horizon) [ Markov property]

The formal decision problem - MDP Given S is a finite state set (with start state s 0 ) A is a finite action set P(s’ | s, a) is a table of transition probabilities R(s, a, s’) is a reward function Policy  (s, t) = a Is there a policy that yields total reward over finite horizon T

Learning Automata Characteristics Learning Automata (LA) are adaptive decision making devices that can operate in environments where  they have no information about the effect of their actions at start of operation — unknown environments  a given action not necessarily produces the same response each time it is performed — non-deterministic environments A powerful property of LA is that they progressively improve their performance by the means of a learning process  combine rapid and accurate convergence with low computational complexity.

Learning Automaton and its interaction with the environment Set of Actions A = { a1, …an } Response β = { 0, 1 }

Methodology Follows a frame based approach which maintains task and attribute histories respect to the domain in focus. The state space is determined by the number of slots in focus. The action space is narrowed to “greeting”, “request all”, “request n slot”, “verify all”, “verify n slot” and close dialogue.

Experiments and Results Our experiments were based on travel planning domain. Speech recognition & speech synthesis modules are implement by.NET SDK framework. DATE scheme was used as a dialogue act recognition agent. The reward in the range of (+10 to -5) is assigned for the best and worst action selection respectively.

Cont…

Evaluation Methodology PRADISE framework Task success: Calculated with help of AVM. System performance:

Conclusions Challenges LA are interesting building blocks to solve different type of RL problems Faster learning Knowledge transfer Less Computational complexity Different LA updates Influence different state observations (POMDP setting)

References I E. Levin, R. Pieraccini and W. Eckert. A stochastic model of human-machine interaction for learning dialogue strategies. IEEE Trans. on Speech and Audio Processing, 8(1), pp. 11–23, M. McTear. Spoken dialogue technology: Toward the conversational user interface. Springer, K. Narendra and M.A.L. Thathachar. Learning Automata: An Introduction. Prentice-Hall International, Inc, A. Nowe and K. Verbeeck. Colonies of learning Automata. IEEE Trans. Syst. Man Cybern B, 32, pp , T. Peak and R. Pieraccini. Automating spoken dialogue management design using machine learning: an industry perspective. Speech Communication, 50, pp , O. Pietquin and T. Dutoit. A probabilistic framework for dialogue simulation and optimal strategy learning. IEEE Transactions on Speech and Audio Processing, 14(2), pp. 589–599, 2006.

References II K. Scheffler and S. Young. Automatic learning of dialogue strategy using dialogue simulation and reinforcement learning. Human Language Technology Conference (HLT), pp 12–19, S. Singh, D. Litman, and M. Kearns. Optimizing dialogue management with reinforcement learning: Experiments with the NJFun system, Journal of Artificial Intelligence Research, 16, pp. 105–133, M. A. L. Thathachar and P. S. Sastry. Networks of Learning Automata: Techniques for Online Stochastic Optimization. Norwell, MA, Kluwer, M. Walker and R. Passonneau DATE:A dialogue act tagging scheme for evaluation of spoken dialogue systems. Proceedings of the Human Language Technology Conference, pp. 1–8, M. Walker, D. Litman and C. Kamm. PARADISE: A framework for evaluating spoken dialogue agents. Proc. of the 5th annual meeting of the association for computational linguistics, pp. 271–280,

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