COMPUTATION OF DIFFERENT OPTICAL-VARIABLES OF LOOMING OBJECTS IN PIGEON NUCLEUS ROTUNDUS NEURONS

Three types of looming-selective neurons have been found in the nucleu s rotundus of pigeons, each computing a different optical variable rel ated to image expansion of objects approaching on a direct collision c ourse with the bird. None of these neurons respond to simulated approa ch toward stationary objects. A detailed analysis of these neurons' fi ring pattern to approaching objects of different sizes and velocities shows that one group of neurons signals relative rate of expansion tau (tau), a second group signals absolute rate of expansion rho (rho), a nd a third group signals yet another optical variable eta (eta). The r ho parameter is required for the computation of both tau and eta, whos e respective ecological functions probably provide precise 'time-to-co llision' information and 'early warning' detection for large approachi ng objects.