Early auditory experience modifies sound localization in barn owls

Abstract

The auditory system localizes sounds by comparing the timing and intensity of sounds arriving at the two ears, and associating specific binaural differences with directions of sounds in space. Thus, location for the auditory system, like stereoscopic depth for the visual system, is a percept created in the brain by a comparison of inputs from two receivers. We considered whether the neural mechanism underlying sound localization is determined entirely genetically, or if it is modified and regulated by auditory experience. The influence of experience on sound localization has been examined previously in various species, including man, with contradictory results1–9. For our study we used the barn owl (Tyto alba) as an experimental model because it localizes sounds with extreme accuracy10,11. By placing a plug in one ear, we disrupted the owl's binaural localization cues and induced large errors in sound localization. We report here that young owls adjusted to the altered cues and regained normal localization accuracy over a period of weeks. However, as the owls aged, their rate of adjustment slowed, and beyond 6–7 months of age, their capacity to adjust was lost or greatly reduced. This plasticity of the sound localization mechanism early in life thus enables the auditory system to establish precise correlations between binaural cues (which vary between individuals) and directions of sounds in space.