Acoustics Research Institute, Austrian Academy of Sciences, Vienna, Austria.
Ear Hear. 2011 Mar-Apr;32(2):198-208. doi: 10.1097/AUD.0b013e3181f4dfe9.
To test localization of sound sources in horizontal and vertical dimensions in cochlear-implant (CI) listeners using clinical bilateral CI systems.
Five bilateral CI subjects listened via their clinical speech processors to noises filtered with subject-specific, behind-the-ear microphones and head-related transfer functions. Subjects were immersed in a visual virtual environment presented via a head-mounted display. Subjects used a manual pointer to respond to the perceived sound location and received visual response feedback via the head-mounted display during the tests. The target positions were randomly distributed in two-dimensional space over an azimuth range of 0° to 360° and over an elevation range of -30° to +80°. In experiment 1, the signal level was roved in the range of ±2.5 dB from trial to trial. In experiment 2, the signal level was roved in the range of ±5 dB.
CI subjects were generally worse at sound localization than normal-hearing listeners tested in a previous study, in both the horizontal and vertical dimensions. In the horizontal plane, subjects could determine the correct side and locate the target within the side at better than chance performance. In the vertical plane, with a smaller level-roving range, subjects could determine the correct hemifield at better than chance performance but could not locate the target within the correct hemifield. The target angle and response angle were correlated as expected. The response angle and signal level range were also correlated, raising concerns that subjects were using only level cues for the task. With a larger level-roving range, the number of front-back confusions increased. The correlation between the target and response angles decreased, whereas the correlation between the level and response angle did not change, which is an indication that the subjects were relying heavily on level cues.
For the horizontal plane, the results are in agreement with previous CI studies performed in the horizontal plane with a comparable range of targets. For the vertical plane, CI listeners could discriminate front from back at better than chance performance; however, there are strong indications that the broadband level, not the spectral profile, was used as the primary localization cue. This study indicates the necessity of new CI processing strategies that encode spectral localization cues.
使用临床双侧人工耳蜗（CI）系统测试 CI 受话者在水平和垂直方向上对声源的定位。
5 名双侧 CI 受话者通过其临床言语处理器，使用特定于受话者的耳后麦克风和头相关传递函数对噪声进行滤波。受话者沉浸在通过头戴式显示器呈现的视觉虚拟环境中。受话者在测试过程中使用手动指针来响应感知到的声音位置，并通过头戴式显示器接收视觉响应反馈。目标位置在 0°到 360°的方位角范围和-30°到+80°的仰角范围以二维方式随机分布。在实验 1 中，信号电平在试验之间的±2.5dB 范围内变化。在实验 2 中，信号电平在±5dB 的范围内变化。
与之前在水平平面上进行测试的正常听力受话者相比，CI 受话者在水平和垂直方向上的声音定位通常较差。在水平平面上，受话者可以确定正确的一侧，并在该侧内定位目标，表现优于随机。在垂直平面上，在较小的电平变化范围内，受话者可以确定正确的半视野，但不能在正确的半视野内定位目标。目标角度和响应角度如预期的那样相关。响应角度和信号电平范围也相关，这表明受话者仅在任务中使用电平线索。随着电平变化范围的增大，前后混淆的次数增加。目标和响应角度之间的相关性降低，而水平和响应角度之间的相关性没有变化，这表明受话者高度依赖于水平线索。
对于水平平面，结果与之前在水平平面上进行的具有类似目标范围的 CI 研究一致。对于垂直平面，CI 受话者可以以高于随机的表现来区分前后；然而，有强烈的迹象表明，宽带水平而不是频谱分布被用作主要的定位线索。本研究表明，有必要采用新的 CI 处理策略来编码频谱定位线索。
