Prosodic Encoding of Informativity: Word Frequency and Contextual Probability Interact with Information Structure

Prosodic Encoding of Informativity: Word Frequency and Contextual Probability Interact with Information Structure Iris Chuoying Ouyang (chuoyino@usc.edu) Elsi Kaiser (emkaiser@usc.edu) Department of Linguistics, University of Southern California 3601 Watt Way, GFS 301, Los Angeles, CA 90089, USA Abstract This study investigates how prosody encodes the extent to which a linguistic element is informative. While most prior work has approached this question from one of the two angles, namely (i) information theory/statistical probability and (ii) discourse-pragmatics/information structure, we focus on the interaction between these two dimensions. Our results show that the prosodic marking of information-structural categories depends on statistical probabilistic factors. Specifically, the post-focus pitch reduction resulting from new-information focus and corrective focus is modulated by the focused word’s frequency and contextual probability, respectively. In terms of pitch, new-information narrow focus patterns like wide focus when the focused word is lexically infrequent, although the two focus types differ when the word has high frequency. Furthermore, corrective narrow focus patterns like wide focus when the focused word is contextually improbable, although the two focus types differ when the word has low contextual probability. We discuss how these results suggest that prosody reflects speakers’ expectation and surprise about the interlocutor’s knowledge state. Our findings highlight the importance of integrating research from the information-theoretical perspective with research from the information-structural perspective, to improve our understanding of prosody. Keywords: informativity, post-focus reduction, interactive design, information structure, focus, information theory 1. Introduction It is widely accepted that prosody can encode the extent to which a linguistic element is informative. Acoustic-phonetic properties of an utterance such as f0/pitch reflect the relative informativity of its components. Most prior work has approached the prosodic encoding of informativity from one of two angles: (i) information structure in a discourse- pragmatic approach or (ii) statistical probability in an information-theoretic approach (see references cited in the remainder of Introduction). In the discourse pragmatics and information structure tradition, acoustic prominence has been shown to be associated with linguistics elements in the foreground, or in focus, which add new information to the discourse. Elements in new-information focus, i.e. those parts of the utterance that are new to the discourse, are acoustically more prominent than given elements, i.e. those that are old to the discourse (e.g. Chen & Braun, 2006; Schwarzschild, 1999). More specifically, material in narrow new- information focus, where only one component of an utterance (e.g. the action, the patient, the location, etc.) is focused, receives greater acoustic prominence than material in wide new-information focus, where an entire utterance with multiple components is focused (e.g. Breen et al., 2010; Eady et al., 1986). It has also been shown that material in contrastive focus, to which alternatives exist in some way, is realized with greater acoustic prominence than non- contrastive material (e.g. Cooper et al., 1985; Couper- Kuhlen, 1984; Katz & Selkirk, 2011; Krahmer & Swerts, 2001). Existing studies across languages have investigated various types of contrastive focus (e.g. Vallduvi & Vilkuna, 1998). We investigated one subtype, namely corrective focus, which serves to correct information conveyed previously in the discourse (see also Breen et al., 2010 and Dik, 1997). On the other hand, in the information theory and statistical probability tradition, a correlation has been found between acoustic reduction and the redundancy, or the predictability of linguistic elements. Probabilistic measurements used to represent the predictability of a linguistic unit include context-independent properties such as frequency and neighborhood density (e.g. Munson & Solomon, 2004; Wright, 2003) and context-dependent properties such as joint probability and conditional probability (e.g. Bell et al., 2003; Pan & Hirschberg, 2000; van Son et al., 1998). Are there connections between information-structural and information-theoretic approaches? As can be seen from the discussion above, these two research traditions have investigated rather different factors of informativity from distinct perspectives, despite their shared interest in informativity and prosody. A limited number of studies in the statistical-probabilistic approach have examined the effect of repeated mention (a repeated word is by definition given, not new, information) on different kinds of linguistic units (e.g. Aylett & Turk, 2004; Baker & Bradlow, 2009; Bell et al., 2009; Pluymaekers et al., 2005). To our knowledge, only one existing study has addressed the interaction between statistical-probabilistic and discourse- pragmatic factors: Baker and Bradlow (2009) found that word frequency influences the amount of reduction that a word undergoes when it is mentioned for a second time; high-frequency words exhibit more shortening upon second mention than low-frequency words. It remains unclear whether other kinds of statistical-probabilistic features also have an impact on the prosodic effects of discourse- pragmatic factors and whether word frequency interacts with other types of information structure in the same say.