Lateralized interhemispheric transfer of color cues: Evidence for dynamic coding principles of visual lateralization in pigeons

Visual feature discrimination tasks in pigeons reveal a right eye/left hemi sphere dominance at the population level. Anatomical studies and lesion dat a show this visual lateralization to be related to asymmetries of the tecto fugal system, which ascends from the tectum over the n. rotundus to the for ebrain. Anatomically, this system is characterized by numerous morphologica l and connectional asymmetries which result in a bilateral visual represent ation in the dominant left hemisphere and a mostly contralateral representa tion in the subdominant right hemisphere. Ontogenetically, visual lateraliz ation starts with an asymmetrical embryonic position within the egg, which leads to asymmetries of light stimulation. Differences in exposure to light stimulation between the eyes result in activity differences between the as cending tectofugal pathways of the left and the right hemisphere, which are transcribed during a critical time span into morphological asymmetries. Th e asymmetries established after this transient period finally start to dete rmine the lateralized processes of the visual system for the entire life sp an of the individual. We now call show that these anatomical lateralization s are accompanied by asymmetries of interocular transfer, which enable a fa ster shift of learned color cues from the dominant right to the left eye th an vice versa. In summary, our data provide evidence that cerebral asymmetr ies are based both on "static" anatomical and on "dynamic process-dependent principles. (C) 2000 Academic Press.