Discrete and continuous modes in speech motor control.
| Number | 812 |
|---|---|
| Year | |
| Drawer | 15 |
| Entry Date | 11/04/1999 |
| Authors | Lofqvist, A., & Gracco, V. L. |
| Contact | |
| Publication | Paper from the symposium Current Phonetic Research Paradigms: Implications for Speech Motor Control. Stockholm, Sweden, August 13-16, 1991. (pp.27-34). |
| url | http://www.haskins.yale.edu/Reprints/HL0812.pdf |
| Abstract | [Introduction] At one level, speech can be described as a sequence of discrete segments. At another level, speech is more properly described as a continuous sequence of articulatory movements and/or a continuously time-varying acoustic signal. While segments are useful for description of speech and most likely have a psychological reality, they do not occur as such in records of articulation. The reason is that coarticulation, coproduction, blending, or aggregation make the gestures associated with different segments overlap. One method of investigating the properties of hypothetical discrete speech motor units is to disrupt ongoing articulation and examine the compensatory effects (cf., Abbs, Gracco, & Cole, 1984; Lofqvist, 1990, for reviews). From detailed examination of the compensatory characteristics it is possible to infer the underlying organization. While much information has been inferred from previous perturbation experiments, a number of limitations can be identified. First, most detailed examinations of compensatory articulatory interactions have focused on temporal and spatial changes in lip and jaw movements (Abbs & Gracco, 1984; Folkins & Abbs, 1975; Folkins & Zimmerman, 1982; Gracco & Abbs, 1985, 1988, 1989) with much less information available on compensations in other articulators (Kelso, Tuller, Vatikiotis-Bateson, & Fowler, 1984; Shaiman, 1989). Although a few studies have demonstrated magnitude changes in articulators outside the lips and/or jaw, such investigations have generally been qualitative in nature focusing on the presence or absence of a significant compensatory response rather than detailing the specific interactions (see Shaiman, 1989 for a notable exception). Recently, Munhall, Lofqvist, & Kelso (submitted) have demonstrated that lip perturbations result in laryngeal changes thereby suggesting articulatory (sensorimotor) coupling across these two systems. A second limitation in previous perturbation studies is almost exclusive focus on a single component in a speech movement sequence. As stated above, speech is a sequence of articulatory events. In order to understand the speech production process, it is critical to obtain information on aspects of the underlying sequencing or serial ordering of continuous vocal tract actions. To date, only two studies have focused on compensatory effects that span more than a single speech gesture (Gracco & Abbs, 1989; Saltzman, Kay, Rubin, & Kinsella-Shaw, 1991). In order to understand the underlying speech motor organization and the implementation mechanism, more detailed investigations are required focusing on larger units of production. The following is a preliminary report of an initial investigation evaluating the distributed nature of the compensatory response to lower lip perturbation focusing on lip/jaw/laryngeal interactions. In addition to the focus on multiple components of the vocal tract, we are attempting to evaluate the local (i.e., the first perturbed gesture) and remote (the following gestures) timing/sequencing effects of speech movement disruption. |
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