Understanding Nasal Emission During Speech Production: A Review of Types, Terminology, and Causality.

There are several different types of nasal emission that can occur during speech due to either velopharyngeal dysfunction or abnormal articulation in the pharynx. Nasal emission can be inaudible or very loud and distracting, depending on the size of the velopharyngeal opening and the physics of the flow. Nasal emission can be obligatory and/or compensatory (due to abnormal structure) or it can be caused by a misarticulation that results in a substitution of a pharyngeal sound for an oral sound, despite normal velopharyngeal structure. Nasal emission can occur on all pressure-sensitive phonemes or it can be phoneme-specific. Although it is generally recognized that the loud and distracting form of nasal emission (called nasal turbulence or nasal rustle) is due to a small velopharyngeal opening, the causality of the distracted sound is debated. This article provides a brief review of the types of nasal emission, the terms used to describe it, and the potential causes. This article also stresses the need for further research to clarify the causality of the sound generated by a small velopharyngeal opening.