PERIPHERAL CONTROL AND LATERALIZATION OF BIRDSONG

Recent studies on several species of oscine songbirds show that they a chieve their varied vocal performances through coordinated activity of respiratory, syringeal, and other vocal tract muscles in ways that ta ke maximum advantage of the acoustic flexibility made possible by the presence of two independently controlled sound sources in their bipart ite syrinx (vocal organ). During song, special motor programs to respi ratory muscles alter the pattern of ventilation to maintain the supply of respiratory air and oxygen to permit songs of long duration, high syllable repetition rates, or maximum spectral complexity. Each side o f the syrinx receives its own motor program that, together with that s ent to respiratory muscles, determines the acoustic properties of the ipsilaterally produced sound. The acoustic expression of these bilater ally distinct, phonetic motor patterns depends on the action of dorsal syringeal adductor muscles that, by opening or closing the ipsilatera l side of the syrinx to airflow, determine the amount each. side contr ibutes to song. The syringeally generated sound is further modified by muscles that control the shape of the vocal tract. Different species have adopted different motor strategies that use the left and right si des of the syrinx in patterns of unilateral, bilateral, alternating, o r sequential phonation to achieve the differing temporal and spectral characteristics of their songs. As a result, the degree of sang latera lization probably varies between species to form a continuum from unil ateral dominance to bilateral equality. (C) 1997 John Wiley & Sons, In c.