The term “mute” describes a person unable to speak, but whether they can make sounds depends entirely on the specific physiological or neurological impairment. For most individuals identified as mute, the inability relates to producing intelligible language, not the complete inability to produce sound. The capacity to vocalize a noise often remains intact, even when the ability to form words is lost.
Vocalization Versus Articulated Speech
The distinction between a simple noise and a word lies in the difference between vocalization and articulated speech. Vocalization is the basic process of creating sound, involving the vibration of the vocal folds within the larynx as air is expelled from the lungs. This produces the raw, non-specific sound, often described as a “buzzy” tone, which is the foundation of the human voice.
Articulated speech is a complex motor and cognitive act that turns raw vocalization into recognizable words. This requires the precise coordination of over 100 muscles in the respiratory system, larynx, pharynx, and oral cavity. Articulators like the tongue, lips, and soft palate modify the air stream and laryngeal tone to form specific phonemes and words.
Producing an intelligible sentence demands specialized neural networks in the brain, including areas like Broca’s and Wernicke’s, which plan and execute linguistic and motor commands. A person can have a functional vocal apparatus capable of producing sound, yet still be unable to speak because the complex neural programming for articulation is impaired.
Physiological Reasons for Impaired Speech Production
One category of impaired speech involves physical damage or absence of the sound-producing structure itself. A laryngectomy, the surgical removal of the larynx, results in the complete loss of the vocal folds, meaning the person cannot produce the basic voiced sound required for speech. Even in this case, they can still produce unvoiced sounds by manipulating the airflow, and many use an electronic larynx to generate a mechanical tone that can then be shaped into speech.
Another major pathway for impaired speech is neurological, typically categorized as aphasia or dysarthria. Aphasia is the loss of the ability to understand or express language, often resulting from a stroke or traumatic brain injury to the brain’s language centers. A person with severe aphasia has a functional vocal tract but the brain cannot generate the correct linguistic plan or motor commands to construct intelligible words.
Dysarthria is a motor speech disorder caused by damage to the nervous system that weakens or paralyzes the muscles controlling speech production. Conditions like Amyotrophic Lateral Sclerosis (ALS) or Multiple Sclerosis (MS) can affect the control of the tongue, lips, vocal cords, and diaphragm. This results in slow or slurred speech that is difficult to understand. The failure is in the execution of the motor plan, not the capacity to generate voice.
A third cause is profound hearing impairment from an early age, which prevents the development of learned speech patterns. Speech acquisition relies heavily on auditory feedback, allowing a child to hear and correct their own vocalizations. Without this feedback loop, the vocal cords may be physically healthy, but the individual never learns the complex motor control to articulate words. They can generally produce a wide range of vocal noises because the physical hardware is intact.
Non-Verbal Sounds That Remain Possible
For individuals whose muteness stems from neurological or developmental causes, or even some forms of laryngeal damage, a variety of non-verbal sounds typically remain possible. These non-speech vocalizations are often reflexive and emotional, relying on more primitive brain pathways that bypass the complex cortical areas used for language. The neural control for innate vocalizations, such as grunts and cries, extends from the brainstem and limbic structures, a system distinct from the voluntary control of language.
Sounds like laughing, crying, and screaming are powerful, emotion-driven vocalizations that require only the basic coordination of the diaphragm and the vocal folds. These noises utilize the vocal apparatus to produce sound of varying pitch and intensity. They do not require the precise movements of the articulators necessary to form consonants and vowels. A person can often scream at full volume or laugh heartily even if they cannot speak.
Several sounds do not require vocal fold vibration at all, meaning they are possible even for a person without a larynx. These unvoiced sounds include:
- A cough
- A gasp
- A sneeze
- A whistle
A cough, for example, is a forceful expulsion of air that generates noise through turbulence in the respiratory tract, not laryngeal vibration. Whistling is created by shaping the mouth and tongue to generate friction against the air current, an articulatory action independent of the voice box.