Xu J, Gooler D M, Feng A S
Department of Physiology and Biophysics, University of Illinois at Urbana-Champaign 61801.
J Acoust Soc Am. 1994 Apr;95(4):2160-70. doi: 10.1121/1.408677.
The effects of sound direction on frequency selectivity of inferior colliculus (IC) neurons were investigated by measuring the neuron's isointensity frequency responses (FRs) to tone bursts emanating from a free-field loudspeaker at several sound levels. The loudspeaker was rotated across the frontal field at 0 degrees elevation through 180 degrees of azimuth (from contralateral 90 degrees or C90 degrees to ipsilateral 90 degrees or I90 degrees). At each frequency, to assess the magnitude of response change with sound direction, the mean spike count obtained at an azimuth was compared to that at C90 degrees. The FR of most IC neurons (75/83 or 90%) was direction dependent. For most of these neurons, bandwidths of FRs were narrower when sounds originated from ipsilateral azimuths. Remarkably, with a change in sound azimuth, some segments of these FRs showed very distinct changes in shape, while other portions of the same FRs remained essentially unchanged. These narrow-band changes associated with restricted portions of the FR, were also exhibited by neurons with direction-dependent frequency-threshold characteristics (Gooler et al., 1993). Additionally, the most frequent direction-dependent change in the FRs occurred in a narrow frequency band around the units' best excitatory frequency.
通过测量下丘（IC）神经元对自由场扬声器在几个声级下发出的短纯音的等强度频率响应（FRs），研究了声音方向对IC神经元频率选择性的影响。扬声器在仰角为0度时，在额平面上从对侧90度（C90度）到同侧90度（I90度）旋转180度方位角。在每个频率下，为了评估响应随声音方向的变化幅度，将在某一方位角获得的平均脉冲计数与在C90度时的平均脉冲计数进行比较。大多数IC神经元（75/83或90%）的FR是方向依赖性的。对于这些神经元中的大多数，当声音来自同侧方位角时，FR的带宽更窄。值得注意的是，随着声音方位角的变化，这些FR的某些部分在形状上显示出非常明显的变化，而同一FR的其他部分基本保持不变。具有方向依赖性频率阈值特征的神经元（Gooler等人，1993）也表现出与FR的受限部分相关的这些窄带变化。此外，FR中最常见的方向依赖性变化发生在单位最佳兴奋频率附近的窄频带内。
