Effects of Anticipatory Coarticulation on Lexical Access

Effects of Anticipatory Coarticulation on Lexical Access Stephen J. Tobin (stephen.tobin@uconn.edu) Department of Psychology, University of Connecticut, Storrs, CT 06269-1020 USA Haskins Laboratories, 300 George St., New Haven, CT 06510 USA Pyeong Whan Cho (pyeong.cho@uconn.edu) Department of Psychology, University of Connecticut, Storrs, CT 06269-1020 USA Haskins Laboratories, 300 George St., New Haven, CT 06510 USA Patrick M. Jennett (pjennett@engr.uconn.edu) Cognitive Science Program, University of Connecticut, Storrs, CT 06269-2054 USA James S. Magnuson (james.magnuson@uconn.edu) Department of Psychology, University of Connecticut, Storrs, CT 06269-1020 USA Haskins Laboratories, 300 George St., New Haven, CT 06510 USA Abstract In order to make progress in studying spoken word recognition, psycholinguists have made the temporary simplifying assumption that the input to word recognition can be approximated by a phonemic transcription (as though this were the product of a speech perception mechanism). This allows one to sidestep the lack of invariance problem and related complications due to coarticulation. Coarticulation refers to the fact that the articulatory gestures of adjacent and even nonadjacent segments overlap, and therefore, so do their acoustic realizations. That is, as you produce one speech sound, you are simultaneously preparing your articulators for upcoming segments, and still experiencing effects of preceding articulations. Coarticulation is often viewed as destructive, as in Hockett's (1955) metaphor of a wringer squishing together a line of easter eggs on a conveyor belt, and a major contributor to lack of invariance. Even when a scientist is cognizant of the fact that the phonemic input assumption is almost certainly incorrect, and she explicitly considers it provisional (until we solve the lack of invariance problem at the phonological level), it has the potential to hide constraints on word recognition (Magnuson, 2008). For example, Salverda, Dahan and McQueen (2003) reported that listeners use subtle prosodic cues (e.g., vowel duration) to anticipate word length and constrain lexical competition. They tracked eye movements as subjects followed spoken instructions to click on pictures on a computer display. When initial vowel duration was consistent with a bisyllabic word, subjects immediately began looking preferentially at items with bisyllabic names. A phonemic transcription also abstracts away from coarticulatory information, which can specify qualities of upcoming segments. Dahan, Magnuson, Tanenhaus, and Hogan (2001) demonstrated that listeners are extremely sensitive to such information. They cross-spliced words (e.g., neck and net) to provide misleading coarticualtory cues to final consonants. Using the visual world paradigm, they found fast, robust effects of such mismatches on lexical activation and competition. These examples are inconsistent with suggestions that coarticulation has a destructive impact on phonetic One of the most challenging unsolved problems in cognitive science is lack of invariance in spoken language. We take the view that variability due to coarticulation is systematic and beneficial. Several recent eye tracking experiments have demonstrated listeners' sensitivity to local coarticulatory cues between adjacent phonemes. We examined sensitivity to longer-range, anticipatory vowel- to-vowel coarticulation, which can spread across multiple syllables. Using a variant of the Visual World eye tracking paradigm (Tanenhaus et al., 1995), we conducted the first on-line test of whether lexical access is sensitive to such subtle, long-range cues, and whether the impact of such cues is modulated by the coarticulation resistance of intervening segments. Lexical access was delayed when misleading anticipatory coarticulation was available in cross-spliced materials. This significantly extends the nature and temporal range of subcategorical cues known to influence on-line sentence comprehension, and demonstrates that lexical access is simultaneously constrained by information at multiple temporal grains. Keywords: Coarticulation; anticipation; garden path; eye tracking. Introduction One of the hardest unsolved problems in cognitive science is lack of invariance in speech. There is a many- to-many mapping between acoustics and percepts, such that the same acoustic information can map to different speech sounds, while different acoustic information can map to the same speech sounds (depending on phonetic context, speaking rate, physical or indexical characteristics of talkers, etc.). This is true of production and perception even for clearly articulated segments and syllables (Ladefoged & Broadbent, 1957; Liberman, Delattre & Cooper, 1952; Peterson & Barney, 1952). The problem is compounded in mapping to words and beyond in conversational speech, where even more variation occurs. For example, Hawkins (2003) describes radical changes in the acoustics of the message I do not know in a progression from careful speech to casual speech ( I dunno , and even more reduced forms). The puzzle, then, is how we reliably map acoustics to words despite (or perhaps with the aid of) all this variation.