Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2005.Includes bibliographical references (p. 75-78).How do people think about things they can never see or touch? The ability to invent and reason about domains such as time, ideas, or mathematics is uniquely human, and is arguably the hallmark of human sophistication. Yet, how people mentally represent these abstract domains has remained one of the great mysteries of the mind. This dissertation explores a potential solution: perhaps the mind recruits old structures for new uses. Perhaps sensory and motor representations that result from physical interactions with the world (e.g., representations of physical space) are recycled to support our thinking about abstract phenomena. This hypothesis is motivated, in part, by patterns observed in language: in order to talk about abstract things, speakers often recruit metaphors from more concrete or perceptually rich domains. For example, English speakers often talk about time using spatial language (e.g., a long vacation; a short meeting). Cognitive linguists have argued such expressions reveal that people conceptualize abstract domains like time metaphorically, in terms of space. Although linguistic evidence for this Conceptual Metaphor Theory is abundant, the necessary nonlinguistic evidence has been elusive.(cont.) In two series of experiments, I investigated whether mental representations that result from physical experience underlie people's more abstract mental representations, using the domains of space and :!I.:e as a testbed. New experimental tools were developed in order to evaluate Conceptual Metaphor Theory as an account of the evolution and structure of abstract concepts, and to explore relations between language and nonlinguistic thought. Hypotheses about the way people represent space and time were based on patterns in metaphorical language, but were tested using simple psychophysical tasks with nonlinguistic stimuli and responses. Results of the first set of experiments showed that English speakers incorporate irrelevant spatial information into their estimates of time (but not vice versa), suggesting that people not only talk about time using spatial language, but also think about time using spatial representations. The second set of experiments showed that (a) speakers of different languages rely on different spatial metaphors for duration, (b) the dominant metaphor in participants' first languages strongly predicts their performance on nonlinguistic time estimation tasks, and (c) training participants to use new spatiotemporal metaphors in language changes the way they estimate time.(cont.) Together, these results demonstrate that the metaphorical language people use to describe abstract phenomena provides a window on their underlying mental representations, and also shapes those representations. The structure of abstract domains such as time appears to depend, in part, on both linguistic experience and on physical experience in perception and motor action.by Daniel J. Casasanto.Ph.D.