Abnormal auditory experience induces frequency-specific adjustments in unit tuning for binaural localization cues in the optic tectum of juvenile owls

Early auditory experience shapes the auditory spatial tuning of neurons in the barn owl's optic tectum in a frequency-dependent manner. We examined th e basis for this adaptive plasticity in terms of changes in tuning for freq uency-specific interaural time differences (ITDs) and level differences (IL Ds), the dominant sound localization cues. We characterized broadband and n arrowband ITD and ILD tuning in normal owls and in owls raised with an acou stic filtering device in one ear that caused frequency-dependent changes in sound timing and level. In normal owls, units were tuned to frequency-spec ific ITD and ILD values that matched those produced by sound sources locate d in their visual receptive fields. In contrast, in device-reared owls, ITD tuning at most sites was shifted from normal by similar to 55 mu sec towar d open-ear leading for 4 kHz stimuli and 15 mu sec toward the opposite-ear leading for 8 kHz stimuli, reflecting the acoustic effects of the device. I LD tuning was shifted in the adaptive direction by similar to 3 dB for 4 kH z stimuli and 8 dB for 8 kHz stimuli, but these shifts were substantially s maller than expected based on the acoustic effects of the device. Most site s also exhibited conspicuously abnormal frequency- response functions, incl uding a strong dependence on stimulus ITD and a reduction of normally robus t responses to 6 kHz stimuli. The results demonstrate that the response pro perties of high-order auditory neurons in the optic tectum are adjusted dur ing development to reflect the influence of frequency- specific features of the binaural localization cues experienced by the individual.