Binaural Diplacusis and Its Relationship with Hearing-Threshold Asymmetry

Binaural pitch diplacusis refers to a perceptual anomaly whereby the same sound is perceived as having a different pitch depending on whether it is presented in the left or the right ear. Results in the literature suggest that this phenomenon is more prevalent, and larger, in individuals with asymmetric hearing loss than in individuals with symmetric hearing. However, because studies devoted to this effect have thus far involved small samples, the prevalence of the effect, and its relationship with interaural asymmetries in hearing thresholds, remain unclear. In this study, psychometric functions for interaural pitch comparisons were measured in 55 subjects, including 12 normal-hearing and 43 hearing-impaired participants. Statistically significant pitch differences between the left and right ears were observed in normal-hearing participants, but the effect was usually small (less than 1.5/16 octave, or about 7%). For the hearing-impaired participants, statistically significant interaural pitch differences were found in about three-quarters of the cases. Moreover, for about half of these participants, the difference exceeded 1.5/16 octaves and, in some participants, was as large as or larger than 1/4 octave. This was the case even for the lowest frequency tested, 500 Hz. The pitch differences were weakly, but significantly, correlated with the difference in hearing thresholds between the two ears, such that larger threshold asymmetries were statistically associated with larger pitch differences. For the vast majority of the hearing-impaired participants, the direction of the pitch differences was such that pitch was perceived as higher on the side with the higher (i.e., ‘worse’) hearing thresholds than on the opposite side. These findings are difficult to reconcile with purely temporal models of pitch perception, but may be accounted for by place-based or spectrotemporal models.

双耳音高复听症（Binaural pitch diplacusis）是一种感知异常现象：同一声音在左耳或右耳呈现时，会被感知为具有不同的音高。现有文献结果表明，与对称性听力损失患者相比，非对称性听力损失个体中该现象的发病率更高、效应量更大。然而，截至目前，针对该效应的研究均采用小样本量，因此该效应的发病率及其与听阈耳间不对称性的关联仍不明确。本研究共纳入55名受试者，其中12名听力正常者、43名听力受损者，并测量了他们进行耳间音高比较的心理测量函数。在听力正常受试者中，观测到双耳间存在具有统计学显著性的音高差异，但该效应通常较小（小于1.5/16个八度，约7%）。在听力受损受试者中，约四分之三的个体存在具有统计学显著性的耳间音高差异。此外，这类受试者中约有一半的音高差异超过1.5/16个八度，部分受试者的差异甚至达到或超过1/4个八度。即便在测试的最低频率500 Hz处，该现象依然存在。音高差异与双耳听阈差值呈弱但显著的相关性，即听阈不对称性越大，音高差异也越大，该关联具有统计学意义。绝大多数听力受损受试者的音高差异方向表现为：听力阈值更高（即"更差"）的一侧，其感知到的音高高于对侧。上述研究结果难以通过纯时域音高感知模型解释，但可基于位置编码模型或谱时域模型进行阐释。