Sensorimotor characteristics of speech motor sequences

Area of Science:

• Motor Control
• Speech Science
• Biomechanics

Background:

• Understanding the neural mechanisms underlying sequential speech movements is crucial for diagnosing and treating speech disorders.
• Somatic sensory feedback plays a significant role in motor control, but its precise influence on speech movement sequencing remains to be fully elucidated.

Purpose of the Study:

• To investigate the role of somatic sensory interactions in the programming of sequential speech movements.
• To differentiate the effects of load perturbation on the timing and magnitude of lip and jaw movements during speech.

Main Methods:

• Subjects produced repeated lip and jaw closing movements for the /p/ sound in 'sapapple'.
• Lower lip perturbation duration was manipulated under two conditions: Load On (LN) and Load On/Off (LNF).
• Electromyography (EMG) and kinematic data were analyzed to compare muscle activity and movement changes for the second /p/ closure.

Main Results:

• Load conditions differentially affected the second /p/ closure, altering upper and lower lip kinematics.
• Upper lip adjustments reflected load duration, while lower lip adjustments did not mirror upper lip changes in magnitude.
• Timing adjustments for both lips were similar, suggesting a separation between magnitude and timing control in speech movements.
• Load perturbation influenced the timing of muscle activity and movement onset, and also modified preceding opening movements.

Conclusions:

• Speech movement sequence programming is a dynamic process influenced by sensory interactions, involving real-time scaling and timing adjustments.
• The observed separation between magnitude and timing control suggests parallel neural system influences.
• Speech motor programs may be based on generalized actions (e.g., oral opening/closing) rather than specific linguistic units.