Hearing impairment induces frequency-specific adjustments in auditory spatial tuning in the optic tectum of young owls

Bimodal, auditory-visual neurons in the optic tectum of the barn owl are sh arply tuned for sound source location. The auditory receptive fields (RFs) of these neurons are restricted in space primarily as a consequence of thei r tuning for interaural time differences and interaural level differences a cross broad ranges of frequencies. In this study, we examined the extent to which frequency-specific features of early auditory experience shape the a uditory spatial tuning of these neurons. We manipulated auditory experience by implanting in one ear canal an acoustic filtering device that altered t he timing and level of sound reaching the eardrum in a frequency-dependent fashion. We assessed the auditory spatial tuning at individual tectal sites in normal owls and in owls raised with the filtering device. At each site, we measured a family of auditory RFs using broadband sound and narrowband sounds with different center frequencies both with and without the device i n place. In normal owls, the narrowband RFs for a given site all included a common region of space that corresponded with the broadband RF and aligned with the site's visual RF. Acute insertion of the filtering device in norm al owls shifted the locations of the narrowband RFs away from the Visual RF , the magnitude and direction of the shifts depending on the frequency of t he stimulus. In contrast, in owls that were raised wearing the device, narr owband and broadband RFs were aligned with visual RFs so long as the device was in the ear but not after it was removed, indicating that auditory spat ial tuning had been adaptively altered by experience with the device. The f requency tuning of tectal neurons in device-reared owls was also altered fr om normal. The results demonstrate that experience during development adapt ively modifies the representation of auditory space in the barn owl's optic tectum in a frequency-dependent manner.