Interaction in planning movement direction for articulatory gestures and manual actions.

Some theories concerning speech mechanisms assume that overlapping representations are involved in programming certain articulatory gestures and hand actions. The present study investigated whether planning of movement direction for articulatory gestures and manual actions could interact. The participants were presented with written vowels (Experiment 1) or syllables (Experiment 2) that were associated with forward or backward movement of tongue (e.g., [i] vs. [ɑ] or [te] vs. [ke], respectively). They were required to pronounce the speech unit and simultaneously move the joystick forward or backward according to the color of the stimulus. Manual and vocal responses were performed relatively rapidly when the articulation and the hand action required movement into the same direction. The study suggests that planning horizontal tongue movements for articulation shares overlapping neural mechanisms with planning horizontal movement direction of hand actions.