Study Notes on Resonance and Nasality in Speech Pathology

Overview of Resonance and Nasality

• Standard Disclaimer for Voice Specialists: Resonance must be categorized within clinical speech parameters. While voice specialists and non-specialists often treat resonance as a non-voice parameter, it is fundamentally linked to voice in the ASH of Big Nine content areas (Voice and Resonance).

• Definition of Resonance: In this context, resonance is primarily defined through nasality.

• Key Parameters of Nasality:
      - Hypernasality: A highly nasal voice quality (e.g., producing oral sounds with nasal resonance).
      - Hyponasality (Denasality): Insufficient nasal resonance on sounds that require it (e.g., sound changes during the production of nasal phonemes).
      - Denasal Vowels: Strictly speaking, there is no such thing as a denasal vowel; a denasal vowel is simply a normal, oral vowel production.

• Control of Nasality: Unlike other voice parameters (breathiness, hoarseness, pitch, glottal fry, hard glottal attack) which occur at the larynx, nasality is controlled at the velopharyngeal point (or port).

• Articulatory Nature: Nasality is often viewed as an articulation issue. The velum acts as one of the articulators, determining whether air enters the nasal cavity.

Phonemic Requirements for Nasality

• Nasal Phonemes in English: There are three specific phonemes in English that require an open velopharyngeal port:
      - $/m/$
      - $/n/$
      - $/ng/$ (the velar nasal sound, which is neither a pure $/n/$ nor a pure $/g/$).

• Oral Phonemes: All other phonemes in English, including vowels, plosives (e.g., $/p, b, t, d, k, g/$), fricatives (e.g., $/s, z, f, v/$), and affricates (e.g., $/ch, j/$), should ideally have zero nasality or nasal airflow.

• Production Differences:
      - The difference between $/b/$ and $/m/$ is solely the velopharyngeal port position. In $/b/$, the port is closed, allowing intraoral pressure to build until the release burst. In $/m/$, the port is open, and air flows through the nose.
      - Hyponasality transforms $/m/$ into a $/b/$ like sound, $/n/$ into a $/d/$ like sound, and $/ng/$ into a $/g/$ like sound.

Hierarchy of Hypernasality Severity

• Assimilation Nasality (Mild):
      - Defined as the influence of one phoneme on the production of another (coarticulation).
      - Normal Context: A small amount of assimilation nasality is normative in rapid conversation (e.g., the vowel in "een" may be slightly more nasal than the vowel in "eat" because the articulators prepare for the upcoming nasal $/n/$).
      - Clinically Significant Context: Occurs in individuals with a "sluggish" velum that moves slowly or fails to close fully/quickly enough, often due to weakness or velopharyngeal dysfunction.

• Nasalized Vowels (Moderate):
      - This occurrs when vowels are consistently produced with nasal resonance regardless of surrounding nasal phonemes.

• Nasal Emission (Severe):
      - Characterized by turbulent puffs of air leaking through the nose during pressure consonants (plosives/stops).
      - In a spectrogram, the "silent period" of a plosive should be silent; in patients with nasal emission, this period contains a hissing or turbulent noise caused by air leakage through a poorly sealed velopharyngeal port.

Assessment of Nasality

• Perceptual Evaluation: The most common method. Clinicians listen for hypernasality, hyponasality, or nasal emission.
      - A Pothole Warning: Mild degrees of hypernasality and hyponasality are often confused by laypeople and beginning clinicians; severe cases are easier to differentiate.

• Nasal Spoon/Mirror Test:
      - A polished nasal spoon or small mirror is placed under the nares during oral phoneme production.
      - Fogging on the surface indicates nasal emission or hypernasality.
      - Fogging may evaporate quickly ( < 1 \, \text{second} ), so close observation is required.

• Pinch Technique:
      - The clinician or patient gently pinches the nares during voicing.
      - If a change in sound is heard during purportedly oral sounds (like an "ah"), hypernasality is present.
      - This test should not be used on nasal sounds ($/m, n, ng/$) as it will naturally distort them.

• Nasometry:
      - Uses a Nasometer (e.g., by KayPentax) consisting of a baffle/dividing plate and two microphones—one for the mouth and one for the nose.
      - Measures Nasalance: The ratio of nasal acoustic energy to total acoustic energy.
      - The 80/20 Rule: A general rule of thumb where nasal sounds should have nasalance scores above $80\%$ and oral sounds should have scores below $20\%$. Values between $20\%$ and $80\%$ are generally abnormal.

• Pressure and Flow Measures:
      - Conducted at institutions such as UNC (notably by Dave Zajek).
      - Much more precise than nasometry for characterizing velopharyngeal action by measuring actual air flows and pressures.

Etiology and Treatment

• Organic Causes: Most resonance issues have a structural or neurological basis.
      - Cleft Palate: The most common cause due to physical separation between the oral and nasal cavities.
      - Tonsillectomy and Adenoidectomy (T&A): Removing adenoid tissue can create temporary hypernasality as the velum must adapt to a new distance from the posterior pharyngeal wall. This usually resolves as muscles heal.
      - Neurological Deficits (e.g., ALS): Insidious, slow onset of hypernasality in an elderly individual can be a first symptom of bulbar-onset ALS.

• Management Guidelines:
      - Treatment Efficacy: Nasality is often not amenable to traditional speech therapy. Hypernasality, especially in children, usually requires surgical or medical intervention.
      - Sluggishness vs. Weakness: A weak muscle is a slow muscle. If the velum is weak, timing issues occur during rapid speech, even if isolated phonemes are clear.
      - Referral Rule: If significant nasality persists $6$ to $9$ months post-surgery after attempted therapy, a surgical consult is necessary. This is a common Praxis/NASPA exam principle.

• Clinical Signs:
      - Facial Grimacing: Patients may scrunch the nose/nares to manually reduce nasal emission during speech.
      - Vocal Fold Nodules: Historically, unrepaired clefts or severe nasal emission could lead to nodules as patients over-adduct the larynx to compensate for the inability to build intraoral pressure.