By examining the metaphors and metonymies reflected in speech-gesture synchrony, this dissertation discusses the relationship between signifiers and the signified content of metaphors and metonymies. The overall aim of this dissertation is to investigate the ongoing abstract thinking processes underlying discourse production. Gestures and speech do not merely duplicate each other; together, they co-express ongoing underlying thinking while speaking. This is because, while verbal language has to be generated following a grammar and lexicon, gestures are produced spontaneously; hence, they can dynamically manifest ongoing mental processes. Additionally, since speech and gestures use different modalities, namely, aural and visual, the quality and the characteristics of signified contents often differ. Looking at speech and gestures together provides us with more access to the complex information contained within our ongoing cognition than examining speech alone would. This dissertation consists of three studies. The first study examines the relationship between verbal and gestural expressions of anger in Japanese discourse while looking at related conceptual metaphors and metonymies. The results show that several conceptual metaphors and metonymies that are reflected in linguistic expressions of anger are also observed in gestures, but they are not always present in the speech accompanying them. This suggests that gestures provide a way to see significant aspects of the conceptualization of emotions at the moment of speaking which we might fail to discover by focusing on speech alone. The second study examines how gestures and linguistic metonymy are coordinated to express one underlying thought. As hypothesized, the results of this study show that gestures and metonymies, taken together, show more information than either taken alone. The final study examines gestures that point concretely to the addressee and their function in discourse. The results show that these deictic gestures establish cohesion in discourse via metonymy. Therefore, I propose that these concrete pointing gestures have abstract status as weIl because the pointing gestures provide a reference point to something that is related to the person to whom they are directed. In conclusion, using speech-gesture synchronization as an investigative tool allows us to see dynamic and hidden aspects of our thinking while speaking. (Mika Ishino)