Middlebrooks J C, Knudsen E I
J Neurophysiol. 1987 Mar;57(3):672-87. doi: 10.1152/jn.1987.57.3.672.
This study examines the influence of external ear position on the auditory spatial tuning of single units in the superior colliculus of the anesthetized cat. Unit responses to broad-band stimuli presented in a free sound field were measured with the external ears in a forward symmetrical position or with one or the other ear turned 40 degrees to the side; the ears are referred to as contra- or ipsilateral with respect to the side of the recording site. Changes in the position of either ear modified the spatial tuning of units. The region of space from which a stimulus was most effective in activating a unit is referred to as the unit's "best area". Whenever the contralateral ear was turned to the side, best areas shifted peripherally and somewhat upward, roughly in proportion to the magnitude of the change in ear position. A turn of the ipsilateral ear to the side had more variable effects, but best areas generally shifted frontally. Best areas located between approximately 10 and 40 degrees contralateral when the ears were forward were least affected by changes in ipsilateral ear position. Changes in ear position also modified the maximum response rates of many units. Units with best areas located within approximately 20 degrees of the frontal midline when the ears were forward exhibited a pronounced decrease in responsiveness when either ear was turned. Units with more peripheral best areas tended to show no change or a slight increase in responsiveness. The influence of ear position on the directionality of the external ears was determined by mapping the cochlear microphonic response to tones or one-third-octave bands of noise before and after turning the ear. When the ears were forward, maximum interaural intensity differences (IIDs) were produced by high-frequency sound sources (greater than or equal to 20 kHz) located 20-40 degrees from the frontal midline and by lower frequency sources located further peripherally. The influence of ear position on the locations from which maximum IIDs were produced was similar to the influence of ear position on unit best areas. Changes in ipsilateral ear position had different effects on high- and low-frequency IIDs that were comparable with the effects of changes in ear position on frontally and peripherally located best areas, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
本研究考察了外耳位置对麻醉猫上丘单个神经元听觉空间调谐的影响。用处于向前对称位置的外耳，或使一只耳朵或另一只耳朵向一侧转动40度的方式，测量了在自由声场中呈现宽带刺激时神经元的反应；耳朵相对于记录部位的一侧被称为对侧耳或同侧耳。任一耳朵位置的改变都会改变神经元的空间调谐。刺激最有效地激活神经元的空间区域被称为该神经元的“最佳区域”。每当对侧耳转向一侧时，最佳区域会向周边且略有向上移动，大致与耳朵位置变化的幅度成比例。同侧耳转向一侧的影响更具变异性，但最佳区域通常向前移动。当耳朵向前时，位于对侧约10至40度之间的最佳区域受同侧耳位置变化的影响最小。耳朵位置的改变也会改变许多神经元的最大反应率。当耳朵向前时，最佳区域位于额中线约20度范围内的神经元，在任一只耳朵转动时，反应性都会显著降低。最佳区域更靠周边的神经元往往反应性没有变化或略有增加。通过绘制转动耳朵前后对音调或三分之一倍频程噪声带的耳蜗微音器反应，确定了耳朵位置对外耳方向性的影响。当耳朵向前时，最大耳间强度差（IID）由位于距额中线20 - 40度的高频声源（大于或等于20 kHz）以及位于更周边的低频声源产生。耳朵位置对产生最大IID的位置的影响，与耳朵位置对神经元最佳区域的影响相似。同侧耳位置的改变对高频和低频IID有不同影响，分别与耳朵位置改变对位于前方和周边的最佳区域的影响相当。（摘要截断于400字）
