This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Linguistics. Please check back later for the full article.
Coarticulation can be characterized as an articulatory effect exerted by one phonetic segment (the trigger) onto another (the target) in the speech chain, for example, anticipatory velar lowering during a vowel preceding a syllable-final nasal consonant (send) or tongue body raising and fronting during a schwa placed next to a palatal consonant (theshore, ashamed). Coarticulatory effects have been generally investigated with reference to a single articulator (e.g., velum, lips, tongue tip, tongue body, jaw, larynx) or a given acoustic parameter (e.g., second formant). It is then convenient to keep this concept separate from gestural coproduction, which refers to the spatiotemporal interaction among different articulatory structures during the realization of one or several successive phonetic segments.
Coarticulation may be measured in space and time. Thus, tongue body raising and fronting effects exerted by palatal consonants on an immediately preceding schwa are predicted to be larger and start earlier than those exerted by the same consonant type on a preceding low or mid-vowel. Moreover, the spatiotemporal effects in question may differ in direction—they may be anticipatory and thus proceed leftwards towards the preceding segment(s), or they may be carryover and thus proceed rightwards towards the following segment(s); it is commonly accepted that anticipatory effects reflect phonemic planning, while carryover effects are mainly associated with the physico-mechanical requirements of the articulatory structures. The magnitude, temporal extent, and direction of the co-articulatory effects are conditioned by the place and manner of articulation of the triggering and target consonants and/or vowels, as well as by the articulatory subsystem involved in closure or constriction formation. Depending on their articulatory characteristics, vowels and consonants may differ regarding coarticulation resistance and aggressiveness, namely, the degree to which they block coarticulatory effects from contextual segments (resistance) and modify the articulatory characteristics of other segments (aggressiveness); thus, in a CV sequence composed of a palatal consonant and a schwa, the palatal segment is more coarticulation resistant and aggressive than the schwa. Other factors affecting coarticulation are segmental position within the word and the utterance and, with respect to word and sentence stress, as well as sequence type (VCV, CC, and so on), speech rate, speaker, and language.
The study of coarticulation provides information about the spatiotemporal mechanisms used by speakers for the production of phonemic sequences, about phonemic planning strategies in speech, and about sound change patterns and assimilatory processes. It has been traditionally assumed that coarticulatory effects are phonetic and thus gradual, variable, and universal, while assimilations are phonological and thus categorical, systematic, and language-specific. Thus, for example, tongue body raising and fronting effects from a palatal consonant during a schwa occur to a greater or lesser extent in any speech production event (coarticulation), but may only be labeled assimilatory if giving rise to a higher and more frontal vowel, such as /e/ or /i/, in a subset of lexical items or across the lexicon of a given language (assimilation). Experimental evidence shows, however, that the division between coarticulation and assimilation is not so straightforward. Indeed, coarticulatory effects may exhibit language-dependent differences (e.g., languages may differ regarding the degree of anticipatory vowel nasalization triggered by a syllable-final nasal consonant), while processes that have been traditionally considered to be assimilatory are far from applying categorically and systematically (e.g., the extent to which /n/ assimilates in place of articulation to a following consonant in English or German may vary with the consonant itself, speaker, prosodic factors, and speech rate).