The role of the frog forebrain andmidbrain in flux, wavelength and movement discrimination was investigated by behavioral testingbefore and after selective ablations of the dorsal anterior thalamus and tectum. Experiments were also performed to determine by which pathways information necessary for these discriminations enters the brain. The results indicate that all of these behaviors depend on Information from the lateral eyes, that the dorsal anterior thalamus is involved in flux and wavelength discrimination and that flux discrimination can be maintained even when only ipsilateral retinal projections to the thalamus remain. Complete bilateral tectal lesions abolished wavelength and movement discrimination and impaired flux discrimination. Incomplete bilateral tectal lesions did not abolish any of the discriminations, but did produce scotomata for movement discrimination. Removal of retinal afferent fibers to the tectum abolished only movement discrimination.