Pigeons trained to discriminate between visual stimuli in a key-pecking task normally show excellent interocular transfer of training (IOT) when trained with only one eye and then tested with the 'naive' eye. When the dorsal supraoptic decussation (DSO) was sectioned and pigeons were then trained monocularly to peck at keys in an interocular transfer experiment, they failed to show normal IOT of a simultaneous horizontal-vertical discrimination. In contrast, another group of pigeons, in which the DSO was sectioned after they had already learned the discrimination with one eye covered, showed excellent IOT postoperatively when the blindfold was moved to the other eye. Since the pigeon uses the normally binocular portion of its retina to scan the discriminative stimuli in a key-pecking task and the DSO carries converging binocular input from the retinorecipient zone of the thalamus to the visual Wulst, the results suggest that IOT in the pigeon is the simple consequence of information reaching both hemispheres from a single eye via converging binocular pathways. Thus, cutting the DSO before training with the first eye eliminates IOT whereas cutting it after training with the first eye does not (since information has already reached the two hemispheres from the normally binocular portion of that eye). These findings complement earlier work showing that IOT is absent in normal pigeons in those situations in which they scan the discriminative stimuli with the monocular portion of their visual fields.