The elastic phrase: modeling the dynamics of boundary-adjacent lengthening

This work examines the relation between phrasal structure and the control and coordination of articulation within a dynamical systems model of speech production. In this context, we review how speakers modulate the spatiotemporal organization of articulatory gestures as a function of their phrasal position. We present computational simulations that capture several important qualitative properties of these phrase boundary effects, such as prosodically-induced local slowing. This slowing is generated by dynamical effects on the activation timecourse of articulatory gestures and is controlled by prosodic gestures or pi-gestures, which share much with the familiar dynamical description of constriction gestures. Prosodic gestures, however, function at boundaries purely to temporally stretch or shrink gestural activation trajectories. This modulation of the "clock-rate" that controls the temporal unfolding of an utterance near junctures is such that the clock slows increasingly as the boundary is approached and speeds up again as the boundary recedes. Viewing phrase boundaries as warping the temporal fabric of an utterance represents a promising confluence of the fields of prosody and of speech dynamics. (C) 2003 Elsevier Science Ltd. All rights reserved.