Data from: Monopolar detection thresholds predict spatial selectivity of neural excitation in cochlear implants: implications for speech recognition

The objectives of the study were to (1) investigate the potential of using monopolar psychophysical detection thresholds for estimating spatial selectivity of neural excitation with cochlear implants and to (2) examine the effect of site removal on speech recognition based on the threshold measure. Detection thresholds were measured in Cochlear Nucleus® device users using monopolar stimulation for pulse trains that were of (a) low rate and long duration, (b) high rate and short duration, and (c) high rate and long duration. Spatial selectivity of neural excitation was estimated by a forward-masking paradigm, where the probe threshold elevation in the presence of a forward masker was measured as a function of masker-probe separation. The strength of the correlation between the monopolar thresholds and the slopes of the masking patterns systematically reduced as neural response of the threshold stimulus involved interpulse interactions (refractoriness and sub-threshold adaptation), and spike-rate adaptation. Detection threshold for the low-rate stimulus most strongly correlated with the spread of forward masking patterns and the correlation reduced for long and high rate pulse trains. The low-rate thresholds were then measured for all electrodes across the array for each subject. Subsequently, speech recognition was tested with experimental maps that deactivated five stimulation sites with the highest thresholds and five randomly chosen ones. Performance with deactivating the high-threshold sites was better than performance with the subjects’ clinical map used every day with all electrodes active, in both quiet and background noise. Performance with random deactivation was on average poorer than that with the clinical map but the difference was not significant. These results suggested that the monopolar low-rate thresholds are related to the spatial neural excitation patterns in cochlear implant users and can be used to select sites for more optimal speech recognition performance.本研究的目标为：(1) 探究利用单极心理物理检测阈值评估人工耳蜗（cochlear implant）使用者神经兴奋空间选择性的潜力；(2) 基于该阈值测量，考察电极位点移除对言语识别的影响。研究对象为使用Cochlear Nucleus®人工耳蜗设备的使用者，针对三种脉冲串（pulse trains）采用单极刺激（monopolar stimulation）模式测量检测阈值：(a) 低速率长时程脉冲串、(b) 高速率短时程脉冲串、(c) 高速率长时程脉冲串。神经兴奋的空间选择性通过前向掩蔽范式（forward-masking paradigm）进行估计：测量前向掩蔽音存在时探测阈值的升高量，并以掩蔽音-探测音间隔作为函数开展分析。当阈值刺激的神经响应涉及脉冲间相互作用（不应期（refractoriness）与阈下适应（sub-threshold adaptation））以及锋电位速率适应（spike-rate adaptation）时，单极阈值与掩蔽模式斜率之间的相关强度会系统性降低。低速率刺激的检测阈值与前向掩蔽模式的扩散程度相关性最强，而针对长时程、高速率脉冲串的该相关性会有所减弱。随后，为每位受试者的电极阵列中所有电极测量低速率刺激的检测阈值。继而使用实验刺激映射（experimental maps）开展言语识别测试，该映射会分别停用阈值最高的5个刺激位点与5个随机选取的刺激位点。结果显示：在安静环境与背景噪声环境下，停用高阈值位点后的言语识别表现均优于受试者日常使用的、所有电极均激活的临床刺激映射（clinical map）表现。随机停用位点后的平均表现则低于临床映射，但该差异未达到统计学显著性。上述结果表明，单极低速率检测阈值与人工耳蜗使用者的神经兴奋空间模式相关，可用于筛选刺激位点以实现更优的言语识别表现。