A topographic instructive signal guides the adjustment of the auditory space map in the optic tectum

Maps of auditory space in the midbrain of the barn owl (Tyto alba) are cali brated by visual experience. When owls are raised wearing prismatic spectac les that displace the visual field in azimuth, the auditory receptive field s of neurons in the optic tectum shift to compensate for the optical displa cement of the visual field. This shift results primarily from a shift in th e tuning of tectal neurons for interaural time difference. The visually bas ed instructive signal that guides this plasticity could be based on a topog raphic, point-by-point comparison between auditory and visual space maps or on a foveation-dependent visual assessment of the accuracy of auditory ori enting responses. To distinguish between these two possibilities, we subjec ted owls to optical conditions that differed in the center of gaze and the visual periphery. A topographic signal would cause the portions of the spac e map representing the central and peripheral regions of visual space to ad just differently, according to the optical conditions that exist in each re gion. In contrast, a foveation-based signal would cause both portions of th e map to adjust similarly, according to the optical conditions that exist a t the center of gaze. In six of seven experiments, adaptive changes were as predicted by a topographic instructive signal. Although the results do not rule out the possible contribution of a foveation-based signal, they demon strate that a topographic instructive signal is, indeed, involved in the ca libration of the auditory space map in the barn owl optic tectum.