Javer A R, Schwarz D W
Rotary Hearing Centre, University of British Columbia, Vancouver.
J Otolaryngol. 1995 Apr;24(2):111-7.
Interaural time difference (ITD), the main cue for localization of low-frequency sound in azimuth, is widely thought to be evaluated according to Jeffress' model. This theory proposes that each of an array of neurons detects coinciding input from both ears, conducted along axonal delay lines, with the azimuth angle corresponding to the activation of selected neurons. Thus, sound source localization is assumed to depend on axon conduction velocities, a relatively fixed parameter. Clinical experience suggests that directional hearing is adaptable. We investigated if sound localization in azimuth could adapt plastically to altered ITDs. We equipped binaural insert hearing aids with adjustable electronic delay lines. Subjects with normal hearing were required to wear these devices during all waking hours for several days. Localization of an invisible sound source was measured in an anechoic room before and at various intervals after introduction of a constant delay in one ear between 171 and 684 mus. Test sounds were high-pass, low-pass and broad-band noises. Introduction of a delay in one ear lead to an immediate displacement of the perceived sound location towards the opposite side. Within hours of exposure, the displacement was reduced, and further normalization of the perceived localization occurred over several days. After removal of the delays sound localization normalized rapidly. We conclude that ITD alterations can lead to plastic adaptation of directional hearing, which cannot rely exclusively on fixed axon conduction velocities. Our results suggest additional mechanisms for directional hearing on the basis ITD.
双耳时间差（ITD）是低频声音方位定位的主要线索，人们普遍认为它是根据杰弗里斯模型进行评估的。该理论提出，一系列神经元中的每一个都能检测到沿轴突延迟线从双耳传来的同步输入，方位角与选定神经元的激活相对应。因此，声源定位被认为取决于轴突传导速度，这是一个相对固定的参数。临床经验表明，定向听力是可适应的。我们研究了方位角中的声音定位是否能通过可塑性方式适应改变后的ITD。我们为双耳插入式助听器配备了可调节的电子延迟线。要求听力正常的受试者在清醒的所有时间佩戴这些设备，持续数天。在一只耳朵引入171至684微秒的恒定延迟之前和之后的不同时间间隔，在消声室中测量不可见声源的定位。测试声音为高通、低通和宽带噪声。在一只耳朵引入延迟会导致感知到的声音位置立即向相反方向偏移。在暴露数小时内，偏移量减小，并且在数天内感知定位进一步恢复正常。去除延迟后，声音定位迅速恢复正常。我们得出结论，ITD改变可导致定向听力的可塑性适应，这不能仅依赖于固定的轴突传导速度。我们的结果表明了基于ITD的定向听力的其他机制。
