Generation of Relative Referring Expressions based on Perceptual Grouping

Generation of Relative Referring Expressions based on Perceptual Grouping Kotaro FUNAKOSHI Department of Computer Science Tokyo Institute of Technology Meguro ˆOokayama 2-12-1, Tokyo 152-8552, Japan koh@cl.cs.titech.ac.jp Satoru WATANABE Department of Computer Science Tokyo Institute of Technology Meguro ˆOokayama 2-12-1, Tokyo 152-8552, Japan satoru w@cl.cs.titech.ac.jp Naoko KURIYAMA Department of Human System Science Tokyo Institute of Technology Meguro ˆOokayama 2-12-1, Tokyo 152-8552, Japan kuriyama@hum.titech.ac.jp Takenobu TOKUNAGA Department of Computer Science Tokyo Institute of Technology Meguro ˆOokayama 2-12-1, Tokyo 152-8552, Japan take@cl.cs.titech.ac.jp Abstract Past work of generating referring expressions mainly utilized attributes of objects and bi- nary relations between objects. However, such an approach does not work well when there is no distinctive attribute among objects. To overcome this limitation, this paper proposes a method utilizing the perceptual groups of ob- jects and n-ary relations among them. The key is to identify groups of objects that are natu- rally recognized by humans. We conducted psy- chological experiments with 42 subjects to col- lect referring expressions in such situations, and built a generation algorithm based on the re- sults. The evaluation using another 23 subjects showed that the proposed method could effec- tively generate proper referring expressions. 1 Introduction In the last two decades, many researchers have stud- ied the generation of referring expressions to enable computers to communicate with humans about con- crete objects in the world. For that purpose, most past work (Appelt, 1985; Dale and Haddock, 1991; Dale, 1992; Dale and Reiter, 1995; Heeman and Hirst, 1995; Horacek, 1997; Krahmer and Theune, 2002; van Deemter, 2002; Krahmer et al., 2003) makes use of attributes of an intended object (the target) and binary rela- tions between the target and others (distractors) to distinguish the target from distractors. Therefore, these methods cannot generate proper referring ex- pressions in situations where no significant surface difference exists between the target and distractors, and no binary relation is useful to distinguish the target. Here, a proper referring expression means a concise and natural linguistic expression enabling hearers to distinguish the target from distractors. For example, consider indicating object b to per- son P in the situation shown in Figure 1. Note that person P does not share the label information such as a and b with the speaker. Because object b is not distinguishable from objects a or c by means of their appearance, one would try to use a binary re- lation between object b and the table, i.e., “A ball to the right of the table”. 1 However, “to the right of” is not a discriminatory relation, for objects a and c are also located to the right of the table. Us- ing a and c as a reference object instead of the ta- ble does not make sense, since a and c cannot be uniquely identified because of the same reason that b cannot be identified. Such situations have never drawn much attention, but can occur easily and fre- quently in some domains such as object arrange- ment (Tanaka et al., 2004). van …

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