Kim Ja Hee, Shim Leeseul, Bahng Junghwa, Lee Hyo-Jeong
Department of Otorhinolaryngology-Head and Neck Surgery, Hallym University College of Medicine, Chuncheon, South Korea.
Laboratory of Brain & Cognitive Sciences for Convergence Medicine, Hallym University College of Medicine, Anyang, South Korea.
Front Neurosci. 2021 Oct 11;15:749824. doi: 10.3389/fnins.2021.749824. eCollection 2021.
Spatial hearing, which largely relies on binaural time/level cues, is a challenge for patients with asymmetric hearing. The degree of the deficit is largely variable, and better sound localization performance is frequently reported. Studies on the compensatory mechanism revealed that monaural level cues and monoaural spectral cues contribute to variable behavior in those patients who lack binaural spatial cues. However, changes in the monaural level cues have not yet been separately investigated. In this study, the use of the level cue in sound localization was measured using stimuli of 1 kHz at a fixed level in patients with single-sided deafness (SSD), the most severe form of asymmetric hearing. The mean absolute error (MAE) was calculated and related to the duration/age onset of SSD. To elucidate the biological correlate of this variable behavior, sound localization ability was compared with the cortical volume of the parcellated auditory cortex. In both SSD patients ( = 26) and normal controls with one ear acutely plugged ( = 23), localization performance was best on the intact ear side; otherwise, there was wide interindividual variability. In the SSD group, the MAE on the intact ear side was worse than that of the acutely plugged controls, and it deteriorated with longer duration/younger age at SSD onset. On the impaired ear side, MAE improved with longer duration/younger age at SSD onset. Performance asymmetry across lateral hemifields decreased in the SSD group, and the maximum decrease was observed with the most extended duration/youngest age at SSD onset. The decreased functional asymmetry in patients with right SSD was related to greater cortical volumes in the right posterior superior temporal gyrus and the left planum temporale, which are typically involved in auditory spatial processing. The study results suggest that structural plasticity in the auditory cortex is related to behavioral changes in sound localization when utilizing monaural level cues in patients with SSD.
空间听觉很大程度上依赖双耳时间/声级线索，对于听力不对称的患者来说是一项挑战。缺陷程度差异很大，且经常有更好的声音定位表现的报道。对补偿机制的研究表明，单耳声级线索和单耳频谱线索在那些缺乏双耳空间线索的患者中促成了不同的行为表现。然而，单耳声级线索的变化尚未被单独研究。在本研究中，使用1kHz的固定声级刺激来测量单侧耳聋（SSD，最严重的听力不对称形式）患者在声音定位中对声级线索的使用情况。计算了平均绝对误差（MAE）并将其与SSD的持续时间/发病年龄相关联。为了阐明这种可变行为的生物学相关性，将声音定位能力与分割后的听觉皮层体积进行了比较。在SSD患者（n = 26）和一只耳朵急性堵塞的正常对照者（n = 23）中，定位表现都是在健侧耳朵一侧最佳；否则，个体间存在很大差异。在SSD组中，健侧耳朵一侧的MAE比急性堵塞的对照组更差，并且随着SSD发病时持续时间更长/年龄更小而恶化。在患侧耳朵一侧，MAE随着SSD发病时持续时间更长/年龄更小而改善。SSD组中跨外侧半视野的表现不对称性降低，并且在SSD发病时持续时间最长/年龄最小的情况下观察到最大程度的降低。右SSD患者功能不对称性的降低与右侧后颞上回和左侧颞平面更大的皮层体积有关，这些区域通常参与听觉空间处理。研究结果表明，在SSD患者利用单耳声级线索时，听觉皮层的结构可塑性与声音定位的行为变化相关。
