The Trough Effect: Implications for Speech Motor Programming

While the existence of the trough effect is unquestioned, its theoretical significance is unknown. A multifaceted instrumental approach – spectrographic, cineradiographic, and vocal tract modeling – was used to document the trough effect in open (V.CV) and closed (VC.V) syllable forms using a symmetrical vowel context surrounding labial stops. Collectively, the results document the trough phenomeon as a momentary deactivation of tongue and/or lip movement after V1 and continuing into the stop closure. This empirical event suggests a segment-by-segment activation pattern as opposed to a diphthongal vowel-to-vowel trajectory with an independent and superimposed consonantal gesture. Quantitative models of VCV coarticulation must incorporate the trough effect in order to more effectively capture the kinematic properties of speech.