Fig. 6. Head-down motoneuron response to a changing e-vector. The light beam was directed to the dorsal surface of the eye. The lower trace monitors polarizer rotation. The maximum signal indicates an e-vector orientation parallel to the long axis of the eyestalk, and the minimum signal indicates an e-vector orientation parallel to the equatorial axis of the cornea. Note the tendency of the discharge rate to peak as the e-vector orientation approaches the long axis of the eyestalk.