Decoupling functional units in speech production using auditory startle

Functionally defined neuromuscular structures, or modules (e.g., agonist-antagonist pairings), may be decoupled when elicited by a startling auditory stimulus (SAS), revealing possible lower-level functional units. The current study examines lip kinematics in SAS-induced responses and uses a 3D FEM biomechanical model to simulate the temporal interaction between facial muscles used in speech. Results show that SAS-elicited bilabial production is subject to displacement discontinuity (i.e., velocity change); this displacement discontinuity appears to be accounted for by the face model simulation results showing temporally decoupled coordination across neuromuscular modules. These findings suggest possible lower-level neuromuscular modules for speech movements that may correspond with long-described articulators in speech production.