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The projection of the cat'smonocular visual fieldto the contralateral and ipsilateral optic tractsdiffered for thebrisk-sustainedand brisk-transientclasses of retinal ganglion cell. For both types all units recorded with receptive field centres more than about 0.5° into the temporal visual hemifield hadcrossedaxons. The transition from crossed coverage of temporal hemifield to uncrossedcoverage of nasal hemifield was complete at about 0.5° nasal for the brisk-sustained units but crossed brisk-transient units were found with receptive fields as far nasal as 15.8°. The 50% crossed/50% uncrossed zone for brisk-transient units was located 1–2° nasal of that for brisk-sustained units.