MOTOR CONTROL IN PRODUCTION AND DEVELOPMENT

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This research focuses on basic problems in the sensorimotor control and development of complex vocal communication in songbirds. Songbirds provide an excellent model in which to study issues important both to students of animal communication and to those of human speech. Except for man, songbirds are the only animal in which learning plays an important role in the development of complex vocal signals. Songbirds were also the first animal model for central lateralization of vocal motor control analogous to cerebral dominance in human speech. Studies on the neuroethology of birdsong provide a way of experimentally evaluating a variety of concepts important to understanding human speech among which are included the possibility of special phonetic processing in the production and perception of vocal signals, the motor theory of speech perception and the function of central lateralization. These experiments utilize a new technique in which microbead thermistors are placed in each bronchus to record air movement associated with respiration and phonation. Respiratory pressure and the pattern of electrical activity of muscles comprising the vocal organ can also be measured. For the first time it is possible to directly monitor the sound produced and motor activity occurring on each side of the intact syrinx during song. Specific questions to be addressed include: What acoustic contribution does each side of the syrinx make to song? How is activity on the two sides coordinated? Can each side act independently of the other? Is song from a normal syrinx lateralized and if so does this originate centrally (analogous to cerebral dominance in human speech) or peripherally (thus being inappropriate as an animal analog of hemispheric dominance in speech)? What are the motor correlates responsible for specific vocal gestures or phonetic elements of song and how do they develop in the young bird? How are the sometimes conflicting, but interdependent, motor demands of respiratory ventilation integrated with song production? What differences with respect to the preceding questions are there between birds which retain a highly variable plastic song as adults verses those with a crystallized, more stereotyped song? The proposed experiments on adult birds thus address fundamental problems of broad interest. These include the peripheral control and execution of complex central motor patterns; the nature and function of lateralized motor control at both the central and peripheral levels; the motor correlates of specific vocal gestures including the possibility of a special phonetic processing for the production of vocal communication; the use of the same peripheral structure in different behaviors such as vocalization and respiration. Studies on young birds will in addition make a significant contribution toward a better understanding of ontogenetic aspects of sensorimotor development of vocalizations for communication; motor correlates of impressionable periods and the possible role of motor learning.