Diplophonia

Diplophonia, also known as diphthongia, is a phenomenon in which a voice is perceived as being produced with two concurrent pitches.<ref>Ward,

 Diplophonia, 
 The Annals of Otology, Rhinology, and Laryngology, 
 1969,
 Vol. 78,</ref> Diplophonia is a result of vocal fold vibrations that are quasi-periodic in nature.<ref>Kiritani, 
 High-speed digital image analysis of vocal cord vibration in diplophonia, 
 Speech Communication, 
 1993,
 Vol. 13,</ref> It has been reported from old days, but there is no uniform interpretation of established mechanisms.<ref name="Yoshioka 1987">

吉岡博英. 二重声の成立機序に関する音響的側面について(link). {{{website}}}. 筑波大学. 1987.

</ref> It has been established that diplophonia can be caused by various vocal fold pathologies, such as vocal folds polyp, vocal fold nodule, recurrent laryngeal nerve paralysis<ref name="Yoshioka 1987" /> or vestibular fold hypertrophy.<ref name="sickness-dictionary">

仮声帯肥大(link). {{{website}}}. sickness-dictionary.jp.

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References

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