VISUAL-ACUITY AND HEMISPHERIC ASYMMETRIES IN PIGEONS

Pigeons and domestic chicks tested under monocular conditions in patte rn distinction tasks generally show higher discrimination performances with the right eye seeing. At least two different mechanisms could me diate this asymmetry: the dominance of the right eye could either be d ue to hemispheric differences in the cognitive operations performed du ring these tasks, or may reflect a lateralization in the spatial frequ ency discrimination capacity of the left and the right eye system. The aim of the present study was to decide between these two hypotheses. Therefore nine adult homing pigeons (Columba livia) were tested with t he left or the right eye seeing in a visual acuity task using high-con trast square wave gratings. Visual acuity, defined as the spatial freq uency at which the psychometric function crossed the 75% correct line was virtually identical for the two eyes with 6.6 for the left and 6.4 c/deg for the right eye. Thus, visual lateralization as demonstrated in various pattern discrimination tasks seems not to depend on asymmet ries in acuity but probably reflects hemispheric differences in the vi sual processing mode.