In humans, speech is produced by a two-component system, consisting of a sound source, e.g., the vibrating vocal folds, and a so-called vocal-tract filter, which is formed by the acoustic resonances of oral and nasal cavities. Characteristics of the latter can be changed by articulatory gestures—the most important of which are tongue movements—resulting in different speech sounds. Although birds and humans share the capability to make very complex vocalizations, it was generally believed that most of birds’ vocal complexity originated from the vocal sound source, the syrinx. The role of vocal-tract articulators, so important in humans, was believed to be only subsidiary in birds, although it has been proposed that parrots, with their fleshy, highly movable tongue, might form an exception.
In the new study, researchers Gabriël Beckers, Brian Nelson, and Roderick Suthers from Indiana University show that tongue movements in Monk parakeets, Myiopsitta monachus, cause changes in their vocal-tract formant frequencies and amplitudes; formants are narrow ranges of sound frequency that form the basis for vowel sounds and are the same types of sound characteristics that are important in human speech. These observations suggest that lingual articulation is involved in the well-known ability of parrots to mimic human speech. Even more intriguingly, lingual articulation may also underlie a speech-like formant system in the natural vocalizations of parrots.
Gabriël J.L. Beckers, Brian S. Nelson, and Roderick A. Suthers: “Vocal-Tract Filtering by Lingual Articulation in a Parrot”
Published in Current Biology, Volume 14, Number 7, September 7, 2004, pages 1592-1597.
Journal
Current Biology