Buildup and Breakdown of Precedence in ITD and ILD

描述（由申请人提供）：定位声音的能力是沟通和环境意识不可或缺的。正常听力的听众通过响应双耳处的信号定时（ITD）和电平（ILD）的耳间差异来将声音定位在水平面中。在普通的收听环境中（例如，房间），准确定位要求听众对由较早到达的入射声音携带的线索而不是由较晚到达的反射声音携带的虚假线索做出响应。事实上，正常听力的听众的定位明显不受回声和混响的影响。与这种观察相关的各种现象统称为优先效应。虽然优先效应在声音定位中的适应性价值是明确的，但关于该效应的重要问题仍然存在。例如，虽然ITD和ILD是不同的声学线索，被认为在听觉脑干中单独处理，但大多数优先发现反映了来自采用耳机ITD或自由场刺激的研究的数据，其中ITD和ILD对定位判断的贡献是不可分割的：关于ILD对优先级的贡献知之甚少，尽管有证据表明ILD是某些听众定位的主要线索，包括越来越多的双侧人工耳蜗使用者。因此，拟议的研究的广泛的长期目标是阐明ITD和ILD的优先效应的单独贡献，以建立一个更完整的和临床信息帐户的声音定位在普通的听音环境。拟议研究的具体目的是：（1）检查听众在重复呈现仅携带ITD或ILD的“源-回波”刺激后对“回波”的敏感性;（2）检查听众在重复呈现携带ITD和ILD组合的“源-回波”刺激后对“回波”的敏感性。来自申请人实验室的最新数据表明，ITD敏感性的时间过程与ILD敏感性的时间过程显著不同。因此，对于第一个目标，初始实验将测试回声抑制对于携带ITD的刺激比对于携带ILD的刺激更鲁棒的假设。为了实现第二个目标，将进行一个额外的实验，以检验“动态”回声抑制取决于对ITD和ILD“图像的敏感性这一假设。“在整个实验中，刺激将通过耳机呈现，以允许独立操纵ITD和ILD线索，回声阈值将通过自适应心理物理程序进行估计。拟议的研究将提供有价值的新的见解，现有的大量的优先效应的文献和独特的作用，ITD和ILD在空间听觉。因此，这项工作将为听力的基本和临床理解提供信息，强调这项建议与NIDCD的使命的相关性。 公共卫生相关性：确定声音来自何处的能力是听力的重要组成部分。虽然日常的收听环境会引入回声和混响，这可能会使确定实际声源的位置变得非常困难，但正常听力的听众在这种条件下非常能够准确定位。拟议的研究建立在已知的这种能力的基础上，以扩大对声音定位的基本理解，并提供对某些听力受损人群（包括双侧人工耳蜗植入用户）的声音定位能力降低的见解。

DESCRIPTION (provided by applicant): The ability to localize sound is integral to communication and environmental awareness. Normal hearing listeners localize sound in the horizontal plane by responding to interaural differences in signal timing (ITD) and level (ILD) at the two ears. In ordinary listening environments (e.g., rooms), accurate localization requires that listeners respond to the cues carried by the early-arriving incident sound rather than the spurious cues carried by later-arriving reflected sound. In fact, localization by normal hearing listeners is remarkably unaffected by echoes and reverberation. The various phenomena associated with this observation are known collectively as the precedence effect. Although the adaptive value of the precedence effect in sound localization is clear, important questions about the effect remain. For example, although ITD and ILD are distinct acoustic cues, thought to be processed separately in the auditory brainstem, most precedence findings reflect data from studies employing headphone ITD or free field stimuli where the contributions of ITD and ILD to localization judgments are inseparable: relatively little is known about the contribution of ILD to precedence, despite evidence that ILD is the dominant cue in localization for some listeners, including a growing population of bilateral cochlear implant users. Thus, the broad long-term goal of the proposed research is to elucidate the separate contributions of ITD and ILD to the precedence effect in order to establish a more complete and clinically informative account of sound localization in ordinary listening environments. The specific aims of the proposed research are (1) to examine listeners' sensitivity to "echoes" following repeated presentations of "source-echo" stimuli carrying only ITD or ILD and (2) to examine listeners' sensitivity to "echoes" following repeated presentations of "source-echo" stimuli carrying combinations of ITD and ILD. Recent data from the Applicant's lab suggests that the time course of ITD sensitivity is substantially different from the time course of ILD sensitivity. Thus, toward the first aim, an initial experiment will test the hypothesis that echo suppression is more robust for stimuli carrying ITD than for stimuli carrying ILD. Toward the second aim, an additional experiment will test the hypothesis that "dynamic" echo suppression depends on sensitivity to both ITD and ILD "images." Across experiments, stimuli will be presented via headphones to allow for independent manipulation of ITD and ILD cues, and echo thresholds will be estimated by an adaptive psychophysical procedure. The proposed research will provide valuable new insight on a large body of existing precedence effect literature and on the unique roles of ITD and ILD in spatial hearing. The work will thus inform both basic and clinical understanding of audition, underscoring this proposal's relevance to the mission of NIDCD. PUBLIC HEALTH RELEVANCE: The ability to determine where sounds are coming from is an important part of hearing. Although everyday listening environments introduce echoes and reverberation that might be expected to make it very difficult to determine the location of actual sound sources, normal hearing listeners are remarkably capable of accurate localization under such conditions. The proposed research builds on what is known about this capacity to expand basic understanding of sound localization and to provide insight on the reduced sound localization abilities of certain hearing impaired populations, including bilateral cochlear implant users.