Adaptation in Sound Localization Processing Induced by Interaural Time Difference in Amplitude Envelope at High Frequencies

BackgroundWhen a second sound follows a long first sound, its location appears to be perceived away from the first one (the localization/lateralization aftereffect). This aftereffect has often been considered to reflect an efficient neural coding of sound locations in the auditory system. To understand determinants of the localization aftereffect, the current study examined whether it is induced by an interaural temporal difference (ITD) in the amplitude envelope of high frequency transposed tones (over 2 kHz), which is known to function as a sound localization cue. Methodology/Principal FindingsIn Experiment 1, participants were required to adjust the position of a pointer to the perceived location of test stimuli before and after adaptation. Test and adapter stimuli were amplitude modulated (AM) sounds presented at high frequencies and their positional differences were manipulated solely by the envelope ITD. Results showed that the adapter's ITD systematically affected the perceived position of test sounds to the directions expected from the localization/lateralization aftereffect when the adapter was presented at ±600 µs ITD; a corresponding significant effect was not observed for a 0 µs ITD adapter. In Experiment 2, the observed adapter effect was confirmed using a forced-choice task. It was also found that adaptation to the AM sounds at high frequencies did not significantly change the perceived position of pure-tone test stimuli in the low frequency region (128 and 256 Hz). Conclusions/SignificanceThe findings in the current study indicate that ITD in the envelope at high frequencies induces the localization aftereffect. This suggests that ITD in the high frequency region is involved in adaptive plasticity of auditory localization processing.

背景：当第二个声音紧随一个时长较长的第一个声音呈现时，其感知位置似乎会偏离第一个声音的位置，即定位/侧化后效（localization/lateralization aftereffect）。此类后效常被认为反映了听觉系统对声音位置的高效神经编码机制。为探究定位后效的决定因素，本研究考察了高频转调音（频率高于2kHz）的幅度包络中的耳间时间差（interaural temporal difference, ITD）是否会诱发该后效——已知该耳间时间差可作为声音定位的有效线索。方法/主要结果：实验1中，要求被试在适应前后调整指针位置，以匹配测试刺激的感知位置。测试刺激与适配刺激均为高频幅度调制（amplitude modulated, AM）声音，二者的位置差异仅通过包络ITD进行操控。结果显示，当适配刺激的ITD为±600μs时，其系统地使测试声音的感知位置向符合定位/侧化后效预期的方向偏移；而ITD为0μs的适配刺激未观察到显著对应效应。实验2采用迫选任务验证了上述适配效应。此外研究还发现，对高频幅度调制声音的适应，不会显著改变低频区域（128Hz与256Hz）纯音测试刺激的感知位置。结论与意义：本研究结果表明，高频包络中的ITD可诱发定位后效。这提示，高频区域的耳间时间差参与了听觉定位加工的适应性可塑性。