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The integration of frequency and phonetic variation in the perception of accented speech

The interaction of lexical frequency and phonetic variation in the perception of accented speech Marie-Catherine de Marneffe (mcdm@stanford.edu) Department of Linguistics, Bldg. 460 Stanford University Stanford, CA 94305-2150 John Tomlinson, Jr. (Tomlinsonj2@cardiff.ac.uk) School of Psychology, Cardiff University Cardiff, CF10 3AT Marisa Tice (middyp@stanford.edu) Department of Linguistics, Bldg. 460, Stanford University Stanford, CA 94305-2150 Meghan Sumner (sumner@stanford.edu) Department of Linguistics, Bldg. 460, Stanford University Stanford, CA 94305-2150 Abstract How listeners understand spoken words despite massive varia- tion in the speech signal is a central issue for linguistic theory. A recent focus on lexical frequency and specificity has proved fruitful in accounting for this phenomenon. Speech percep- tion, though, is a multi-faceted process and likely incorporates a number of mechanisms to map a variable signal to meaning. We examine a well-established language use factor — lexical frequency — and how this factor is integrated with phonetic variability during the perception of accented speech. We show that an integrated perspective highlights a low-level perceptual mechanism that accounts for the perception of accented speech absent native contrasts, while shedding light on the use of in- teractive language factors in the perception of spoken words. Keywords: speech perception, cross-accent perception, lexi- cal frequency, phonetic variation. Introduction A single word is produced differently each time it is ut- tered by one speaker. A single speaker naturally produces a wide array of sound tokens that differ greatly in any number of acoustic values — amplitude, F 0 , duration, for- mant transitions, and so on. Each of these acoustically distinct tokens must be understood sometimes as a single sound (within-category), and other times as different sounds (across-category). A central issue is how listeners, oftentimes with no prior experience with a speaker, learn to navigate through this variation to perceive two variants of a token as instances of the same word or two different words. This is particularly challenging considering that minimal differences between words are oftentimes meaningful. Theories of speech perception that are sensitive to vari- ation, both phonetic and phonological, have typically fo- cused on language use factors to explain how listeners ac- complish the task of mapping a variable signal onto mean- ing (Goldinger, 1996; Johnson, 1997; Newman, Clouse, & Burnham, 2001; Pierrehumbert, 2002). One factor that plays an important role in this mapping task is frequency, or how often a linguistic unit is produced (or experienced by a lis- tener). We know that frequently produced units come with perceptual benefits, e.g., in recognition time, (Dahan, Mag- nuson, & Tanenhaus, 2001; Forster, 1976; Fox, 1984; Gros- jean, 1980; McClelland & Rumelhart, 1981). For example, Fox (1984) found that listeners made more b responses to words in a bad–dad continuum than to syllables in a ba– da continuum when asked to identify the initial sound in the word. He attributed this to a categorization bias toward fre- quent lexical items, showing that we can get Ganong-like (lexical bias) effects with lexical frequency over and above categorical word/non-word effects. Similar effects have been shown for units smaller than a word (e.g., frequent phono- logical variants, Connine, 2004; Deelman & Connine, 2001) and units larger than a word (e.g., chunks of commonly co- occurring words, Arnon & Snider, 2010). Lexical frequency is also a factor shown to influence both the production and perception of spoken words. For example, Jurafsky, Bell, Gregory, and Raymond (2001) showed that frequent words are shorter in duration than infrequent words. Examining the perception of lexically-specific phonological variants, LoCasto and Connine (2002) found that frequent words that typically occur with a reduced vowel in the first syllable (e.g., police) are recognized faster and more accu- rately with a reduced vowel than with a full initial vowel. On the other hand an infrequent word, like obese, that is most often produced with a full vowel, is recognized faster and more accurately with a full vowel. Their study thus shows that listeners are sensitive to phonological variant frequency differences across words of a similar phonological shape. These behavioral patterns are the result of years of expe- rience and exposure with a native language (English). As listeners, we must also map variable speech with less famil- iar speech patterns, and these speech patterns oftentimes use contrasts that are novel to listeners. To circumvent this issue, a number of studies have examined the perception of regional