Surgical transection of the basal optic root in Rana pipiens leads to substantial increases in prey-orientation latencies for stimuli presented in the contralateral visual field. In general, the greater the reduction in retinal innervation of nBOR, the greater the postoperative increase in prey-orientation latencies. The results support Herrick's earlier suggestion that the accessory optic system may be substantially involved in early activation and temporal modulation of visuomotor behaviors mediated via mesencephalic circuits.