title: Selectivity for interaural time difference in the owl's midbrain.
abstract: The barn owl uses the interaural difference in the timing of sounds to determine the azimuth of the source. When the sound has a wide frequency band, localization is precise. When localizing tones, however, the barn owl errs in a manner that suggests that it is confused by phantom targets. We report a neural equivalent of these phenomena as they are observed in the space-specific neuron of the owl's inferior colliculus. When stimulated with a tone, the space-specific neuron discharges maximally at interaural time differences (ITDs) that differ by one period of the stimulus tone. Changing the stimulus frequency changes the period of the ITD-response functions, but 1 ITD evokes, in most neurons, a maximal response, regardless of frequency. This ITD is the characteristic delay (CD). When stimulated with noise, there is a maximal response only to ITDs at or near the CD. Thus, the space-specific neuron can unambiguously signal the CD, provided that the signal contains more than 1 frequency. The preferential response to a single ITD, which is observed with noise stimuli, was also observed when the summed waveform of the best frequency and another tone, F2, was presented. The response of the space-specific neuron to these 2-tone stimuli could not be accounted for by the summing or averaging of the ITD-response functions obtained with the best frequency or F2 alone, suggesting that nonlinear neural processes are involved.
mesh_terms: D000161:Acoustic Stimulation; D000818:Animals; D001307:Auditory Perception / Q000502:physiology*; D001717:Birds / Q000502:physiology*; D005071:Evoked Potentials; D005260:Female; D007245:Inferior Colliculi / Q000502:physiology; D008297:Male; D008636:Mesencephalon / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D013016:Sound; D013017:Sound Localization / Q000502:physiology; D013997:Time Factors