Data_Sheet_1_Interaural asymmetry of dynamic range: Abnormal fusion, bilateral interference, and shifts in attention.zip

Speech information in the better ear interferes with the poorer ear in patients with bilateral cochlear implants (BiCIs) who have large asymmetries in speech intelligibility between ears. The goal of the present study was to assess how each ear impacts, and whether one dominates, speech perception using simulated CI processing in older and younger normal-hearing (ONH and YNH) listeners. Dynamic range (DR) was manipulated symmetrically or asymmetrically across spectral bands in a vocoder. We hypothesized that if abnormal integration of speech information occurs with asymmetrical speech understanding, listeners would demonstrate an atypical preference in accuracy when reporting speech presented to the better ear and fusion of speech between the ears (i.e., an increased number of one-word responses when two words were presented). Results from three speech conditions showed that: (1) When the same word was presented to both ears, speech identification accuracy decreased if one or both ears decreased in DR, but listeners usually reported hearing one word. (2) When two words with different vowels were presented to both ears, speech identification accuracy and percentage of two-word responses decreased consistently as DR decreased in one or both ears. (3) When two rhyming words (e.g., bed and led) previously shown to phonologically fuse between ears (e.g., bled) were presented, listeners instead demonstrated interference as DR decreased. The word responded in (2) and (3) came from the right (symmetric) or better (asymmetric) ear, especially in (3) and for ONH listeners in (2). These results suggest that the ear with poorer dynamic range is downweighted by the auditory system, resulting in abnormal fusion and interference, especially for older listeners.

对于双耳人工耳蜗植入（bilateral cochlear implants, BiCIs）且双耳言语识别能力存在显著不对称性的患者，其较好耳的言语信息会对较差耳造成干扰。本研究旨在采用声码器（vocoder）模拟人工耳蜗处理流程，评估青年正常听力（younger normal-hearing, YNH）与老年正常听力（older normal-hearing, ONH）受试者的双耳言语感知模式，即每侧耳如何影响感知效果，以及是否存在单侧耳主导的情况。研究中对各频谱带的动态范围（dynamic range, DR）进行了对称或非对称的调控。我们提出如下假设：若因双耳言语理解不对称而出现异常的言语信息整合，则受试者在报告呈现至较好耳的言语时，会表现出非典型的准确率偏好，且双耳间会出现言语融合现象（即同时呈现两个单词时，单词报告的次数增加）。三项言语实验条件的结果显示：(1) 当双耳同时呈现相同单词时，若单侧或双侧耳的动态范围降低，言语识别准确率会下降，但受试者通常只会报告听到一个单词。(2) 当双耳分别呈现元音不同的两个单词时，随着单侧或双侧耳动态范围降低，言语识别准确率以及双词报告的占比均持续下降。(3) 当双耳呈现先前研究证实可发生语音融合的押韵词（如bed和led，融合为bled）时，随着动态范围降低，受试者反而表现出干扰效应。在条件(2)和(3)中，受试者报告的单词均来自右侧耳（对称条件下）或较好耳（非对称条件下），这一现象在条件(3)以及条件(2)中的老年正常听力受试者中尤为明显。上述结果表明，听觉系统会降低对动态范围较差耳的权重，进而引发异常的融合与干扰效应，老年受试者的这一表现尤为显著。