ALTHOUGH functional asymmetries in the course of visual information process
ing have been known for a long time in humans as well as in non-human speci
es, the structural basis of these asymmetries is largely unknown. We now re
port that due to an asymmetry of commissural projections in the pigeon the
left nucleus rotundus of the ascending tectofugal visual system predominant
ly represents inputs from both eyes while the right nucleus rotundus mainly
represents the contralateral left eye. We suggest that a comparable organi
zation exists for several asymmetries in humans. A representation of both h
emifields can provide the dominant hemisphere with direct access to all sti
mulus features when objects cross the vertical meridian. NeuroReport 9: 412
7-4130 (C) 1998 Lippincott Williams & Wilkins.