Neglect after section of a left telencephalotectal tract in pigeons

The effects of unilateral and bilateral lesions of the telencephalotectal fibres of the tractus occipitomesencephalicus (OM) were studied in pigeons in a successive visual pattern discrimination. On alternate sessions the animals performed the task with both eyes open or sight restricted to one or the other eye. Unilateral lesions of the left OM led to severe deficits in the total number of pecking responses emitted under both monocular and binocular conditions. Pigeons with lesions of the right OM showed no deficits and the animals with bilateral lesions had an impaired performance only in the binocular condition. The percent correct discrimination performance of all experimental pigeons were at the same level as that of the control group. The results are discussed in the context of visual lateralization in birds. It is suggested that the deficits reflect a sensory neglect through deactivation of neurons in the deep tectal laminae which are known to have projections to reticular nuclei of the brainstem.