Abstract
Neurons in the developing optic tectum adjust their tuning to auditory localization cues in response to chronic monaural occlusion so that auditory spatial fields align with visual receptive fields (VRFs). We tested whether this adaptive adjustment of auditory tuning requires visual instruction. Both eyelids were sutured closed at the same time that one ear was occluded in two barn owls that were 1 month old. After 70 and 100 d, respectively, the tuning of units to interaural level difference (ILD) and to interaural time difference (ITD) was measured. These data were compared with equivalent data from 15 normal owls. Unit tuning to ITD was shifted from normal in both of the monaurally occluded owls. In one owl, ILD tuning was also clearly shifted. In the other owl, the map of ILD was flipped upside down and adaptive adjustments in ILD tuning could not be assessed. Instead, adjustments in ILD tuning were observed following removal of the earplug with the eyelids kept closed. Unit tuning was monitored at several sites in the tectum for 1 month after earplug removal using chronically implanted electrodes. Then, ILD tuning was resampled across the entire tectum. Both measures indicated shifts in ILD tuning in response to removal of the earplug in the second blind owl. In both animals, the magnitude of the shifts in ILD tuning and ITD tuning was smaller than has been observed previously in monaurally occluded but sighted owls. The results demonstrate that the brain can make adaptive adjustments in ILD and ITD tuning in response to early monaural occlusion even without the guiding influence of vision.