Generating Non-Linear Narratives
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INTERNATIONAL INSTITUTE OF INFORMATION TECHNOLOGY, HYDERABAD Generating Non-Linear Narratives by Vinay Chilukuri A thesis submitted in partial fulfillment for the degree of Masters by Research in Computer Science. Cognitive Science Lab June 2011 INTERNATIONAL INSTITUTE OF INFORMATION TECHNOLOGY, HYDERABAD Certificate It is certified that the work contained in this thesis, titled `Generating Non-Linear Narratives' by Vinay Chilukuri has been carried out under my supervision and is not submitted elsewhere for a degree. Date: Advisor: Prof. Bipin Indurkhya iii \A story should have a beginning, a middle, and an end... but not necessarily in that order." Jean-Luc Godard. INTERNATIONAL INSTITUTE OF INFORMATION TECHNOLOGY, HYDERABAD Generating Non-Linear Narratives by Vinay Chilukuri Advisor: Dr. Bipin Indurkhya Abstract Stories play a crucial role in our day-to-day lives. Apart from the entertainment sector, they are also being utilized in different areas of games, education and training. The ability to generate rich stories similar to human authored ones is of significance in story generation research. Along with the content of the story the manner in which it is presented is an important factor in effective storytelling. Though a lot of development happened in auto- matic story generation, most of it ignored the way in which the story could be presented. This thesis deals with a presentation aspect of the story, the order in which the events could be narrated, in order to make it more engaging than that of the chronological versions generated by many story generation systems. We hypothesize that cognitive engagement is manifested when a narrative is deviated from its chronological order without affecting the ease of comprehension. Narratives with events presented in out of chronology are termed non-linear. From a computational perspective, given n events of a story, the total orderings possible are n!. Generating an order in random would affect the comprehension of the material. We have studied how the comprehension of the viewers was affected upon changing the presentation order of the events, by employing a commercial feature film. Using these experimental results along with previous theory from narrative comprehension, we arrive at an algorithm that generates different presentation orders of a story by assessing the amount of processing load required for processing an order of events. Using the principles of the event-indexing model, a cognitive model of narrative comprehension, a function was devised that calculates the processing load, by taking input, the desired amount of non-linearity that could be imparted into the story. An experimental evaluation is undertaken in order to test the generated narratives by our system, corresponding to the different input levels of non-linearity, in terms of engagement. We have obtained results that, for the story employed, increasing the non-linearity up to a medium level did not produce any change in the difficulty in comprehension and thus contributing to engagement. However, it was observed that higher levels of non-linearity led to a decrease in engagement and that, character inconsistencies present in the story had a negative affect on the engagement of the material. Acknowledgements I would like to whole heartedly thank my research advisor, Prof. Bipin Indurkhya, for supporting my idea since its inception. Without his consent, this idea of mine would not have materialized into a full blown research project. He has given me great independence in choosing and pursuing my topic of interest and carrying it forward. Under his supervision, I have learned about what is research and how to do it. Sincerely, this research in an interesting field would not have been possible without his support. I like to thank Amitash Ojha for constantly helping me out with any problem I had. His experience and knowledge were immensely useful for my study. Specifically, his help on experiment design and statistical analysis facilitated my work. Without his questioning, I might not have been able to identify the finer aspects and problems involved with my work. I cherish the philosophical talks, the metaphoric language and the plight that we shared before the night of paper submission deadlines. He has been a mentor and more than that a great friend. I would like to thank Saraschandra Karanam for his immense help and advice on the prob- lems that I presented to him. Because of his advice on many matters related to both my work and the issues of the University, my work here was completed in a smooth manner. He urged me to complete my thesis as soon as possible and get over with it. We shared many good moments on discussing a number of topics ranging from research to culture and to films. I also cherish the fun table-tennis matches, the dinners and the late night movie goings that we had together. I'd like to sincerely thank Apara Ranjan for constantly questioning me and enabling me to bring out a research problem from an inquisitive idea that I had. Discussions with her introduced me to behavioral research and helped me to streamline my thoughts. There will be dark times and there will be light. I had, perhaps, the darkest phase of my life. And then, there were Pradeep and Pujitha. I never believed that one could make best friends after completing college and while doing their Masters. I was so wrong. These amazing friends helped me to come out of a black hole that I was experiencing during my stay at this Institution. A meeting in a creating writing class brought me two friends for life. All the moments with Pradeep about films, culture, behavior and life are so enriching that I think that he is a comrade-in-arms for me. I feel short of words to describe the amazing support Pujitha has given me through these years of my Masters. A thank you seems pale to what she has done. Each and everything that we shared together has to be cherished. I have realized how important it is to be around the right set of people. It is amazing when some one brings a great enthusiasm in you and make you work better. Mahesh is an vi awesome friend, with whom I share a great bond talking about gaming, music and movies. I appreciate his encouragement for my research when I used to discuss it with him. Mahesh, Pradeep and Pujitha gave me the best of times, making my mind saner in an environment to concentrate on my work. Without my fellow batchmates, I would not have come out of this quagmire. The amazing fun times I had in the shady restaurants with Vijay, Sai Deepak and Sandeep were great. I would specially want to thank Vijay for putting up with all my crazy rants right from the start of entering this Institution. I'd like to thank Yogi for experiencing the hazy nights with me and sharing all the problems we experienced as postgraduate students. He is a great friend. It is so good to meet people who have the same passion as yours. Vamshi is a fellow lab member but a good friend with whom I passionately talk about films and life. There are few people who understand my obsessions with films and he is also in the same boat with me. His constant rants to quickly complete my thesis and get into making a film were energizing. I would also like to specifically thank my dear friends, Sharmi, GSK, Vedanth, Harshita, Koumudhi and Meher without whom there would be a part missing out of my life here. I would like to extend my thanks to all my fellow members of the Cognitive Science Lab for supporting me in my research. Without the environment of all these people, this thesis would not have been possible. I cannot imagine myself completing my work in any other environment as good as this. Last but not the least and most importantly, I would like to thank Hans Zimmer for com- posing those beautiful soundtracks. I would definitely not have completed a single report, a paper or my thesis without listening to those amazing scores. I strongly feel that his scores talk about the ability of a man to achieve anything. I used to feel that I am solving an important problem for the world while listening to his music. It has become an integral part of me that I cannot do without it anymore. I owe my productivity to Hans Zimmer's music. Thank you very much. Vinay Chilukuri. Contents Declaration of Authorship iii Abstract v Acknowledgements vi List of Figures xi List of Tables xiii 1 Introduction1 1.1 Problem Statement & Approach . .3 1.2 Contributions . .4 1.3 Layout of the Thesis . .5 2 Background Study7 2.1 Narrative Theory . .7 2.2 Engagement . 10 2.3 Narrative Generation . 12 2.3.1 Story Generation: Computational perspective . 12 2.3.2 Sjuzhet Generation/Narrative Generation . 14 2.3.2.1 Prevoyant . 15 2.3.2.2 Montfort's Research in Interactive Fiction - The nn system . 17 2.3.3 Discourse Generation . 18 2.4 Narrative Comprehension . 19 2.4.1 Event Indexing Model . 20 2.5 Our work . 21 3 Experimental Study of Narrative Comprehension 23 3.1 Theory . 23 3.2 Method . 25 3.2.1 Experiment 1 . 25 3.2.2 Results . 28 3.2.3 Experiment 2 . 30 3.2.4 Results . 31 ix Contents x 3.3 Discussion . 32 4 Generating Non-linear Narratives 35 4.1 Problem Revisited . 35 4.2 Obtaining Engagement by Narrative Variation in Order . 36 4.3 Defining Non-linearity . 37 4.4 Design of the Algorithm . 38 4.4.1 Calculating the Degree of Non-linearity .