Nasal Emission Terminology Should be Evidence Based and Consistent with Physiology and Perceptual-Acoustic Characteristics

Nasal Emission Terminology Should be Evidence Based and Consistent with Physiology and Perceptual-Acoustic Characteristics (1)David J. Zajac, PhD, CCC-SLP, ASHA Fellow

Coauthor of Evaluation and Management of Cleft Lip and Palate: A Developmental Perspective

The term “cleft palate speech” has often been used to refer to hypernasality, nasal air emission, reduced oral air pressure, and compensatory articulations of speakers who exhibit velopharyngeal inadequacy (VPI). Hypernasality is defined as excessive resonance of the nasal cavity during production of vowels and voiced consonants. Nasal air emission refers to the audible escape of air during the production of high-pressure oral consonants, especially voiceless consonants. Reduced oral air pressure is the flip side of nasal air emission. When air escapes through the nose, some oral air pressure is lost. Thus, oral pressure consonantsespecially voiceless ones—may be produced with reduced oral air pressure and perceived as weak or reduced in intensity. Compensatory articulations are maladaptive gestures that are produced at the glottis or in the pharynx as a way to circumvent a faulty velopharyngeal valve. The use of glottal stops to replace oral stops is a classic example of a compensatory articulation. Hypernasality, nasal air emission, and reduced oral air pressure are passive (or obligatory) symptoms of VPI. This means that the symptoms occur as a direct consequence of incomplete velopharyngeal closure. Compensatory articulations, however, are active (or learned) behaviors and may not occur in every individual.

Although obligatory nasal air emission is a core characteristic of VPI, many confusing, overlapping, and inaccurate terms have been used to describe its perceptual manifestation. The literature is replete with terms such as audible nasal air emission, nasal turbulence, nasal rustle, and passive nasal frication. Because the velopharynx and nasal passage are complex anatomical structures— which may be significantly altered due to both congenital defects and surgical interventions associated with cleft lip and palate—the variety of terms used to describe nasal air emission should not be too surprising. Numerous other terms have been used to describe nasal air emission that is part of active (or learned) nasal fricatives and will not be discussed here. The reader is referred to Zajac (2015) for a discussion of active nasal fricatives as an articulatory error. Rather, this article will focus on terminology used to describe passive or obligatory nasal air escape.

A Brief History of Current Terminology

McWilliams, Morris, and Shelton in the first and second editions of Cleft Palate Speech (1984, 1990) described nasal air emission as occurring along a continuum. First, it could be visible but inaudible, detectable only by holding a mirror under the nostrils of a speaker to see fogging as a result of the air emission. In such a case, the nasal airflow is laminar, moving in relatively smooth fashion, and does not become turbulent, or noise producing. Clinically, visible nasal air emission typically occurs in speakers who have adequate but not complete velopharyngeal closure and normal resonance. Although visible nasal air emission should be noted when it occurs in a speaker, there are no treatment implications.

McWilliams et al. (1984, 1990) described a second type of nasal air emission that they called audible. In this case, nasal airflow encounters some resistance or constriction, speeds up, and becomes turbulent or noise producing. McWilliams et al. noted that the sound of audible nasal air emission could be simulated by forcefully exhaling through the nose. In this situation, the soft palate is relaxed and airflow becomes turbulent as it is forced through the anterior nasal valve, the smallest cross-sectional area of the nose (Proctor, 1982). The anterior nasal valve is located approximately 1 centimeter into the entrance of the nose and is defined by the confluence of three anatomical structures—the nasal septum medially, the lateral nasal cartilage, and the anterior part of the inferior turbinate. Clinically, audible nasal air emission typically occurs in speakers who have large velopharyngeal gaps and moderate to severe hypernasality. In such cases, however, the hypernasality is the most salient symptom and the audible nasal air emission may actually be difficult to hear, especially if the speaker has normal anterior nasal resistance or uses reduced respiratory effort while speaking. It must be emphasized that the perceptual characteristic of audible nasal air emission is a frication-like noise that is caused by turbulent airflow (see Figure 1), similar to oral fricatives.

McWilliams et al. (1984, 1990) described a third type of nasal air emission that they termed “nasal turbulence.” They stated that this was characterized by “extra turbulent noises” that were created in the presence of “marked intranasal resistance.” McWilliams et al. noted that by having the speaker blow the nose, nasal turbulence was sometimes eliminated, suggesting that the source of the extra noise was mucous related. Of importance, McWilliams et al. emphasized that nasal turbulence was a more severe form of nasal emission in that the noise generated was especially distracting to listeners.

In the fourth edition of Cleft Palate Speech, Peterson-Falzone, Hardin-Jones, and Karnell (2010) stated that either increased nasal or velopharyngeal resistance could be the source of the extra noises of nasal turbulence. Specifically, they suggested that the extra noises could arise from either vibration of soft tissue or displacement of mucus that pools in a constriction. Kummer (2014) referred to nasal turbulence as “nasal rustle” and attributed its distinctive sound to the bubbling of secretions in a small velopharyngeal port. Clinically, nasal turbulence (or rustle) is typically associated with speakers who exhibit relatively small velopharyngeal gaps.

Perceptual and Acoustic-Spectral Characteristics

Most clinicians can easily distinguish between “audible nasal air emission” and “nasal turbulence” during live evaluations. The former is characterized by relatively quiet, frication-like noise that is generated at the exit of the nose; the latter is characterized by a relatively loud, posterior noise that often has a flutter-like component. Sally Peterson-Falzone, during a discussion session at the 2014 Annual Meeting of the American Cleft Palate-Craniofacial Association, aptly described this component as a “velar raspberry.” Most clinicians readily identify the flutter or raspberry quality as the perceptual essence of nasal turbulence. The physiologic mechanism that generates this noise, however, is controversial. As indicated above, Kummer (2014) attributes the noise to bubbling of secretions in the velopharyngeal port, as often observed during nasoendoscopy. Conversely, Zajac and Preisser (2015) attribute the noise primarily to soft tissue vibration (flutter) at the velopharyngeal port, perhaps with some noise generated secondarily by mucous displacement.  Zajac and Preisser state that the tissue vibration likely involves the marginal edges of the soft palate that come close to but do not firmly contact the posterior pharyngeal wall. Under such a condition, the marginal edges of the velum are likely to vibrate, similar to vocal-fold vibration that is caused by aerodynamic-myoelastic forces. To be sure, Trost (1981) described a blurring or “fluttering” of the velopharyngeal port during radiographic assessment of speakers who produced posterior nasal fricatives.

Zajac and Preisser (2015) provided acoustic-spectral evidence of tissue flutter in children with repaired cleft palate who exhibited nasal turbulence. They recorded 30 children using the oral and nasal microphones of the nasometer while the children repeated various syllables containing voiceless stops and fricatives. Zajac and Preisser then examined the separately recorded nasal audio signal to perceptually and spectrally identify instances of either nasal turbulence or audible nasal emission during the stop and fricative segments of the consonants. Figure 1 shows an example of a child who produced “audible nasal emission” during production of /pi/. The figure shows the oral and nasal audio signals and the spectrogram of the nasal audio signal. During the stop gap of the indicated /p/ segment, there is evidence of aperiodic, frication-like (turbulent) noise in the spectrogram. The noise is relatively high in frequency, consistent with turbulence generated at the anterior nasal valve.

Figure_1_Zajac_blog

Figure 1. Acoustic and spectral evidence of “audible nasal emission” characterized by nasal turbulence. The speech sample was “say pi pi pi again.”

In contrast, Figure 2 shows an example of a child who produced “nasal turbulence” during production of /pi/.  The nasal spectrogram in Figure 2 is clearly different from Figure 1. In Figure 2, the spectrogram shows both aperiodic, frication-like noise and “extra noise.” The extra noise, however, is periodic as indicated by the regularly spaced, dark vertical striations extending through the spectrogram, indicating tissue vibration or flutter. In addition, the aperiodic component is lower in frequency than the aperiodic noise in Figure 1, consistent with a velopharyngeal (posterior) noise source. Audio playback of the nasal signal in Figure 2 is consistent with the description of nasal turbulence as loud and distracting.

Figure_2_Zajac_blog

Figure 2. Acoustic and spectral evidence of “nasal turbulence” characterized by velar flutter and turbulence. The speech sample was “say pi pi pi again.”

Evidence-Based Terminology

Craniofacial speech-language pathologists have generally accepted the terms “audible nasal emission” and “nasal turbulence” (or “rustle”). This is somewhat surprising given the foregoing discussion and acoustic evidence. Even without such evidence, these terms are not especially descriptive perceptually or accurate relative to physiology. The term “nasal turbulence” (or “rustle”) is especially problematic for two reasons. First, it is the velopharyngeal port that is the primary noise source, not the nasal cavity. To be sure, it is possible that some noise may also be generated anteriorly, especially if the speaker has marked resistance at the nasal valve. Second, and more important, the perceptually salient characteristic, in most cases, is quasiperiodic tissue vibration or flutter, not aperiodic noise (turbulence). The perceptual saliency of the flutter is evident by the dark vertical striations in the spectrogram of Figure 2, indicating the most energy or intensity. Zajac and Preisser (2015), however, noted that the flutter component was quite variable across and even within speakers, with flutter absent at times. The variability in flutter is likely due to multiple factors, including changes in velopharyngeal port configuration, tissue biomechanics—which also may be affected by the presence of mucus, and speech production parameters such as loudness or respiratory effort level.

Given the above, can more descriptive terms be used and accepted? Table 1 summarizes the primary noise sources, perceptual attributes, and acoustic-spectral characteristics of currently accepted terms; the table also lists some suggested alternative terms. In the case of audible nasal emission, the term anterior nasal turbulence is suggested. As seen in the table, this term is consistent with both the source location and mechanism that generates the audible emission. In the case of nasal turbulence, likely to have variable perceptual expression, two terms are suggested. Velar flutter is suggested when the perceived noise consists primarily, or exclusively, of a periodic component (i.e., a velar raspberry). As shown in Figure 2, however, aperiodic noise often accompanies velar flutter. In such a case, specification of velar flutter with posterior nasal turbulence is appropriate. Finally, if posterior turbulence is the primary, or exclusive, perceptual component, then the term posterior nasal turbulence is suggested. Although “velopharyngeal” may be more accurate relative to the primary source of the turbulence, the use of “posterior” is still descriptive. It should also be noted that the use of anterior and posterior is consistent with terminology used to describe active nasal fricatives that are learned behaviors (Zajac, 2015).

Table 1. Source, Perceptual, and Spectral Characteristics of Audible Nasal Emission and Nasal Turbulence with Suggested Alternative Terms

Current Term Primary Noise Source Perceptual Attribute Spectral Characteristic Suggested Term
Audible nasal emission Anterior nasal valve Frication-like noise Relatively high frequency aperiodic noise Anterior nasal turbulence
Nasal turbulence/rustle Velopharyngeal port Flutter or raspberry-like sound* Periodic modulation of noise (vertical striations) Velar flutter
Nasal turbulence/rustle Velopharyngeal port Frication-like noise** Relatively low frequency aperiodic noise Posterior nasal turbulence

* May be inconsistent. ** Likely to occur with velar flutter.

Although the suggested terms are more numerous, and may appear more complicated, clinicians can easily master their use with continuing education to expand their knowledge base and refine their clinical perceptual skills. New or inexperienced clinicians may also benefit by audio-recording their clients with either a standard microphone or the nasometer and examining the recorded signal(s) for evidence of turbulence and/or flutter. Some audio examples of anterior nasal turbulence and velar flutter with and without posterior nasal turbulence can be found on the companion website to Evaluation and Management of Cleft Lip and Palate: A Developmental Perspective.

References

Kummer, A. W. (2014). Cleft palate and craniofacial anomalies: Effects on speech and resonance (3nd ed.). Clifton Park, NY: Cengage Learning.

McWilliams, B. J., Morris, H. L., & Shelton, R. (1984). Cleft palate speech. St. Louis, MO: Mosby.

McWilliams, B. J., Morris, H. L., & Shelton, R. (1990). Cleft palate speech (2nd ed.). St. Louis, MO: Mosby.

Peterson-Falzone, S. J., Hardin-Jones, M. A., & Karnell, M. P. (2010). Cleft palate Speech (4th ed.). St. Louis: Mosby.

Proctor, D. F. (1982). The upper airway. In D. F. Proctor & I. B. Anderson (Eds.), The nose: Upper airway physiology and the atmospheric environment. New York, NY: Elsevier Biomedical Press.

Trost, J. E. (1981). Articulatory additions to the classical description of the speech of persons with cleft palate. Cleft Palate Journal, 18, 193–203.

Zajac, D. J. (2015). The nature of nasal fricatives: Articulatory-perceptual characteristics and etiologic considerations. SIG 5 Perspectives on Speech Science and Orofacial Disorders, 25, 17–28.

Zajac, D. J., & Preisser, J. (2015). Influence of age and phonetic context on velar flutter as a component of nasal turbulence in children with repaired cleft palate. Cleft Palate-Craniofacial Journal , Sept. 29, online ahead of print.


About the Author

David J. Zajac, PhD, CCC-SLP, is professor in the Department of Dental Ecology, School of Dentistry, and adjunct in the Division of Speech and Hearing Sciences, Department of Allied Health Sciences, School of Medicine at the University of North Carolina at Chapel Hill. He also serves as director of speech-language pathology in the Craniofacial Center.

Dr. Zajac completed his master’s degree and doctoral degree in communicative disorders at the University of Pittsburgh. He has more than twenty-five years of experience in the assessment and treatment of children and adults with craniofacial disorders. His research interests include the acoustics and aerodynamics of speech production by normal individuals and those with cleft palate. His research has been funded by the National Institutes of Health for more than fifteen years. He has presented numerous research papers, written six book chapters, and authored or coauthored more than forty research articles. Dr. Zajac is a Fellow of the American Speech-Language-Hearing Association and past associate editor for the Journal of Speech, Language, and Hearing Research.

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