Single-unit recordings in the frog''s optic tectum have demonstrated the existence of a systematic spatial separation between the direct contralateral and indirect ipsilateral excitatory receptive fields. Marked differences in this spatial organization were found between paralyzed and anesthesized animals.Significant latency differences were found between sustained (class I/II) and transient (class III) contralateral fibers. Corresponding latency differences were also seen in ipsilaterally driven responses. It is suggested that there may be at least two different classes of ipsilateral fibers.The existence of binocular interaction at the level of the afferent terminal arborizations was investigated, utilizing temporally asynchronous dichoptic stimulation. No such phenomena were seen in curarized animals. These findings are discussed in terms of possible velocity and direction sensitivity mechanisms.