Predicative Metaphors Are Understood as Two-Stage Categorization: Computational Evidence by Latent Semantic Analysis

Predicative Metaphors Are Understood as Two-Stage Categorization: Computational Evidence by Latent Semantic Analysis Akira Utsumi (utsumi@se.uec.ac.jp) Maki Sakamoto (sakamoto@hc.uec.ac.jp) Department of Systems Engineering The University of Electro-Communications 1-5-1, Chofugaoka, Chofushi, Tokyo 182-8585, Japan Department of Human Communication The University of Electro-Communications 1-5-1, Chofugaoka, Chofushi, Tokyo 182-8585, Japan Abstract In this paper, we address the problem of how people under- stand predicative metaphors such as “The rumor flew through the office”, and argue that two-stage categorization is the pro- cess via which predicative metaphors are understood. In the two-stage categorization process, the verb of a predicative me- taphor (e.g., fly) evokes an intermediate category, which in turn evokes a metaphorical category of action or state to be attributed to the target noun (e.g., rumor), rather than directly creating a metaphorical category as argued by Glucksberg’s (2001) categorization theory. We test our argument by means of computer simulation experiment in which the meanings of predicative metaphors are computed from the representations of the verb and the noun in a multidimensional semantic space constructed by latent semantic analysis. In the simulation, three algorithms for predicative metaphor comprehension, i.e., two-stage categorization, categorization and comparison, are compared in terms of how well they mimic human interpreta- tion of 30 predicative metaphors. The simulation result was that the two-stage categorization algorithm best mimicked hu- man interpretation of predicative metaphors, but the compari- son model yielded the best performance in the case of less apt metaphors. These findings suggest that predicative metaphors, in particular apt metaphors, are understood via a two-stage cat- egorization process, but less apt metaphors may possibly be understood via a comparison process. Keywords: Metaphor comprehension; Predicative metaphor; Two-stage categorization; Computational modeling; Latent se- mantic analysis demonstrated that the level of abstraction of a verb’s referent was related to the metaphoricity of a predicative metaphor, such finding does not necessarily mean that the verb directly evokes a metaphorical category in metaphor comprehension. In this paper, therefore, we address the mechanism of pred- icative metaphor comprehension and argue that predicative metaphors are understood via a two-stage categorization pro- cess, which is an extended view of Glucksberg’s categoriza- tion theory. We test our argument by means of computer sim- ulation of metaphor comprehension. For this purpose, we use a semantic space constructed by latent semantic analy- sis (LSA) (Landauer & Dumais, 1997) and provide a com- putational model of the two-stage categorization process, to- gether with computational models of other possible processes for metaphor comprehension (Utsumi, 2006). In the com- puter simulation, we examine how well the two-stage cate- gorization model mimics human interpretations of predica- tive metaphors as compared to the other comprehension mod- els. The model that achieves the best simulation performance can be seen as embodying the most plausible comprehension mechanism of predicative metaphors. Note that our study dif- fers from other LSA-based metaphor studies (e.g., Kintsch, 2000; Lemaire & Bianco, 2003) in that we use the LSA-based methodology to obtain novel findings on metaphor compre- hension, while they only simulate the known findings. Predicative Metaphor Comprehension Introduction How do people understand predicative metaphors (i.e., ex- pressions that involve the metaphorical use of a verb) such as “The rumor flew through the office”? Although a con- siderable number of studies (e.g., Bowdle & Gentner, 2005; Gentner, Bowdle, Wolff, & Boronat, 2001; Glucksberg, 2001; Utsumi, in press) have been made on the cognitive mecha- nism of nominal metaphors (i.e., expressions that involve the metaphorical use of a noun) such as ‘My job is a jail”, very little attention has been paid to the comprehension mecha- nism of predicative metaphors. The cognitive linguistic re- search on metaphor (e.g., K¨ovecses, 2002; Lakoff & John- son, 1980) has addressed predicative metaphors as manifes- tations of the conventionalized, conceptual metaphors. How- ever, these studies do not explore how the conceptual meta- phors are constructed, i.e., how a set of correspondences or mappings are made between the source domain and the target domain. On the other hand, Glucksberg (2001, 2003) argues that people comprehend predicative metaphors via a catego- rization process as they do for nominal metaphors. However, no clear empirical evidence has been provided for his argu- ment. Although Torreano, Cacciari, and Glucksberg (2005) As we mentioned above, one candidate theory of predica- tive metaphor comprehension is Glucksberg’s (2001, 2003) categorization theory. The categorization theory addresses mainly nominal metaphors and argues that people understand nominal metaphors by seeing the target concept as belonging to the superordinate metaphorical category exemplified by the source concept. Glucksberg (2001) also argues that predica- tive metaphors function very much as do nominal metaphors; just as nominal metaphors use vehicles that epitomize certain categories of objects or situations, predicative metaphors use verbs that epitomize certain categories of actions. Accord- ing to this theory, for example, a predicative metaphor “The rumor flew through the office” is comprehended so that the verb fly through evokes an ad hoc category of action such as “to move quickly” or “to spread rapidly and soon disappear” and such action is attributed to the target rumor, as illustrated in Figure 1. Against the categorization theory of predicative metaphors, we propose a two-stage categorization theory. The intuitive idea behind two-stage categorization is that correspondences between the actions literally expressed by the verb and the