Is the squirrel monkey larynx lateralized biomechanically?

Squirrel monkey larynges were dissected, mounted on a pseudotracheal tube, and phonated via the flow of compressed heated and humidified air. Synchronized audio and video signals were digitized and analyzed with a signal processing workstation. Image analysis algorithms measured the change in glottal area due to the movement of the left and right vocal folds, respectively, and measured the change in location of both vocal folds during phonation. The results show that the squirrel monkey larynx is capable of both unilateral and bilateral oscillation. In the unilateral case, oscillation is virtually confined to the left vocal fold. The converse of this has not been observed. In the case of bilateral oscillation, the folds may oscillate synchronously in phase, asynchronously out of phase, or at different fundamental frequencies. The results are consistent with the idea that the biomechanical properties of the left and right vocal folds differ with the left fold capable of oscillation at lower subglottal pressures and greater amplitudes. Changes in vocal fold elongation and adduction change the coupling between the two folds and produce different regimes of oscillation. Squirrel monkeys appear to employ intentional shifts between different regimes of phonation to expand the size of the vocal repertoire.