JAW MUSCLE (EMG) ACTIVITY AND AMPLITUDE SCALING OF JAW MOVEMENTS DURING EATING IN PIGEON (COLUMBA-LIVIA)

During each phase of the pigeon's eating sequence, jaw opening amplitu de (gape) is adjusted to the size of the food object; first prior to c ontact (Grasping), again in positioning the food (Stationing), and fin ally, during its movement through the oral cavity (Intraoral Transport ). Part I of this study examined jaw movement kinematics during ingest ion of different size food pellets to determine the relative contribut ion of velocity and rise time variables. Part II specified the muscle activity patterns mediating each phase of the eating sequence, and det ermined how these patterns are modulated to produce adjustments of gap e size. The relative contribution of velocity and rise time variables to the control of gape differs in each phase of the eating sequence. H owever, for any pellet size, variations in opening rise time may funct ion in a compensatory manner to minimize gape ''undershooting''. Each phase of the eating sequence is mediated by a characteristic muscle ac tivity pattern. The adjustment of gape size to pellet size involves sy stematic modulation of this pattern, and the parameters modulated diff er in the different phases in a manner which may reflect the functiona l requirements of each phase.