Facial Muscles in Phonetics

  • Lips and Face as Articulators

    • Lips and face serve as visible and touchable articulators in speech.

    • They provide rich visual and tactile feedback which is crucial for speech production and perception.

    • Due to their direct accessibility, they are useful for studying feedback mechanisms like visual perception and touch-based communication, such as the Tadoma method.

  • Feedback in Speech Production and Perception

    • Despite focusing on feedforward models in phonetics, feedback is essential in the real-world processing of speech.

    • The variability of lip and facial movements helps provide external feedback through visual and tactile channels.

    • Research by Ménard et al. (2009) illustrates that visually impaired speakers of French show reduced acoustic vowel contrasts, highlighting the role of visual feedback in vowel articulation.

    • Sighted speakers utilize visual cues from interlocutor's faces to refine their speech, integrating visual input with their production.

  • Visual and Tactile Information in Speech Perception

    • Visual cues from lips and face enhance speech perception, especially in noisy environments, as shown in studies by Sunby & Pollack (1954).

    • Visual information can modify auditory speech perception, demonstrated by the McGurk & MacDonald (1976) effect.

    • Tactile feedback enables individuals who are blind or deaf to perceive speech through direct contact with the speaker's face and neck using methods like Tadoma.

  • Orbicularis Oris Muscle (OO)

    • The OO muscle is critical for lip movements and functions like a sphincter.

    • It is composed of multiple fiber layers:

    • Superficial Layer: Located just under the skin, it allows for fine-tuning lip shaping and facial expressions.

    • Deep Layer: Found near bone and connective tissues, it provides strength for lip closure and pressure generation essential for speech (e.g., bilabial sounds).

  • Concentric Organization of Orbicularis Oris

    • The OO is organized in concentric rings around the mouth:

    • Marginal Part (OOm): Inner zone producing rounded, unprotruded lips. Essential for producing front rounded vowels like [y].

    • Peripheral Part (OOp): Outer zone for lip protrusion, necessary for producing back rounded vowels such as [u] and [o].

    • Some languages use these contrasting lip shapes phonemically.

  • Functionality of the OO Muscle

    • Contraction patterns differ:

    • OOm Contraction: Creates inrounded shapes (e.g., in [i]).

    • OOp Contraction: Produces outrounded shapes (e.g., in [u]).

    • The superior (OOs) and inferior (OOi) parts work independently, enabling complex movements essential for articulation.

  • Facial Muscles in Speech

    • Buccinator Muscle: Coordinates with OO to shape lips, maintains intraoral pressure, and assists in eating (chewing, sucking).

    • Risorius Muscle: Known as the "laugh muscle", helps create a sideways mouth spread.

    • Mentalis Muscle: Works to produce pouting actions and supports movements of the lower lip.

    • Levator Labii Superioris (LLS): Raises the upper lip, originating from the lower eye orbit.

    • Zygomaticus Major and Minor: Vital for producing smiles; the major raises mouth corners while the minor opens the upper lip.

    • Depressor Anguli Oris Muscle: Pulls upper lip down, aiding in frowning.

    • Depressor Labii Inferioris: Lowers and spreads the lower lip.