Representation of the visual streak in visuotopic maps of the cat's superior colliculus: influence of the mapping variable.

A series of visuotopic maps has been prepared from recordings of electrical potentials related to W-cell afferent activity in the cat's superior colliculus. These maps clearly exhibit an expected exaggeration of the representation of the upper visual field, due to tilt of the retina's visual streak in the 'position of paralysis'. This asymmetry disappears when the visual field's coordinate system is rotated by an angle equal to the tilt of the axis of the nasal streak. Previously published maps, based on recordings from postsynaptic collicular units, have failed to reflect this tilt of the nasal visual streak, perhaps in part because the centers of unit receptive-fields are biased estimators of the retinal origin of axons terminating near a collicular recording site.