Thalamic neurons in birds receive photic input from the contralateral eye only and thus are monocular for object vision.Surprisingly, we found by single-cell recording from the lateral-eyed pigeon that a population of visual cells in the nucleus opficus principalis thalami, homologue of the mammalian lateral geniculate nucleus, can encode retinal luminance in both eyes.These thalamic cells are classified into four types characterized respectively by bilateral enhancement, bilateral suppression, contralateral enhancement/ipsilateral suppression or contralateral suppression / ipsilateral enhancement of firing rates when light is applied alternately to either eye.Their ipsilateral responses recorded after the ipsilateral eye is enucleated are similar to those when the eye is intact.The latency of ipsilateral responses is identical to that of contralateral ones regardless the ipsilateral eye is intact or enucleated.The sum of contralateral and ipsilateral responses evoked in a single neuron by individual eye stimulation is equivalent in strength to the total responses by simultaneous stimulation of both eyes.