The influence of early auditory and visual experience on the representation of auditory spatial cues in the barn owl forebrain

The experiments described in this dissertation were designed to investigate the capacity for adaptive, experience-based plasticity in the representation of auditory spatial cues in the central auditory system of the barn owl. The first two studies demonstrate the influence of early visual and auditory experience on the representation of auditory spatial cues in the archistriatal gaze fields (AGF), a forebrain region that plays an important role in auditory localization and gaze control. Visual experience was manipulated by raising young owls with prismatic spectacles that displaced the visual field in the horizontal plane. Prism-reared owls exhibited systematic changes in unit tuning for interaural time difference (ITD), the principal cue used for horizontal localization. These changes were adaptive in that they tended to restore appropriate associations between ITD values and locations in the visual field. Auditory experience was manipulated by raising young owls with an acoustic filtering device that caused frequency-specific changes in ITD and interaural level difference (ILD), the principal cue used by the owls for vertical localization. Device-reared owls exhibited adaptive changes in ITD and ILD tuning in the AGF.; The third study demonstrates that early auditory experience, but not early visual experience influences the representation of ITD in the primary source of auditory input to the forebrain, the auditory thalamus (nucleus ovoidalis). These findings indicate that the representation of auditory space can be adjusted at different stages in the forebrain auditory localization pathway and suggest that different learning rules may guide adaptations to auditory and visual experience in this pathway.; The fourth study investigates the influence of age and previous experience on the capacity for adaptive adjustments of frequency-specific ITD tuning in the midbrain auditory localization pathway. Although the capacity to make adaptive adjustments of ITD tuning in response to experience with the acoustic filtering device declined sharply as owls reached adulthood, certain types of plasticity were observed in adults. The ability to recover a normal representation of ITD following the restoration of normal hearing was retained in adult owls. Moreover, the range of ITD representations possible in adulthood was extended by juvenile experience.