| The experiments that comprise this thesis shed new light on two general questions in neuroscience. First, how does the brain process sensory stimuli? Second, how do environmental conditions---spatial, temporal, and contextual---shape the moment-to-moment processing of sensory stimuli? These two questions were addressed by studying the midbrain localization pathway of barn owls. Together, these experiments provide insights into the processing of sensory information in the auditory midbrain and may provide a link between short-term processing of sensory signals and long-term neural plasticity required to maintain the alignment between representations of visual and auditory space.; Chapter Two demonstrates that specific types of experience are extremely influential in driving neural plasticity. Allowing adult owls to hunt live prey revealed a much greater ability to adapt to novel sensory experience than was previously understood. This result demonstrates that the specific context in which experiences occur can dramatically alter an animal's response. Auditory plasticity induced in hunting owls was more robust and consistent than auditory plasticity induced in non-hunting owls.; Chapter Three demonstrates that visual stimuli influence auditory responses in the external nucleus of the inferior colliculus. These experiments show that visual stimulation modulates the gain of neural responses to auditory stimuli in the ICX in a space-specific manner. The visual modulation of auditory responses in the ICX reveals an important role for vision in the moment-by-moment processing of auditory information, and provides a possible mechanism for the long-term guidance of auditory plasticity in the ICX.; Chapter Four describes a mechanism by which neurons in the optic tectum (OT) predict the future locations of moving auditory stimuli. A main function of the OT is to direct an owl's gaze towards salient stimuli in the environment. This experiment shows that the spatial properties of auditory receptive fields in the OT depend upon the speed and direction of a stimulus. More specifically, the distribution of auditory responses in the OT adapts to the velocity of an auditory stimulus in a manner that compensates for sensorimotor delays. |
