Imsiecke Marina, Krüger Benjamin, Büchner Andreas, Lenarz Thomas, Nogueira Waldo
Department of Otolaryngology, Hannover Medical School, Hanover, Germany.
Department of Otolaryngology, Hannover Medical School, Hanover, Germany; Cluster of Excellence 'Hearing4All', Hanover, Germany.
Hear Res. 2018 Jul;364:25-37. doi: 10.1016/j.heares.2018.04.003. Epub 2018 Apr 9.
In order to investigate the temporal mechanisms of the auditory system, psychophysical forward masking experiments were conducted in cochlear implant users who had preserved acoustic hearing in the ipsilateral ear. This unique electric-acoustic stimulation (EAS) population allowed the measurement of threshold recovery functions for acoustic or electric probes in the presence of electric or acoustic maskers, respectively. In the electric masking experiment, the forward masked threshold elevation of acoustic probes was measured as a function of the time interval after the offset of the electric masker, i.e. the masker-to-probe interval (MPI). In the acoustic masking experiment, the forward masked threshold elevation of electric probe stimuli was investigated under the influence of a preceding acoustic masker. Since electric pulse trains directly stimulate the auditory nerve, this novel experimental setup allowed the acoustic adaptation properties (attributed to the physiology of the hair cells) to be differentiated from the subsequent processing by more central mechanisms along the auditory pathway. For instance, forward electric masking patterns should result more from the auditory-nerve response to electrical stimulation, while forward acoustic masking patterns should primarily be the result of the recovery from adaptation at the hair-cell neuron interface. Electric masking showed prolonged threshold elevation of acoustic probes, which depended significantly on the masker-to-probe interval. Additionally, threshold elevation was significantly dependent on the similarity between acoustic stimulus frequency and electric place frequency, the electric-acoustic frequency difference (EAFD). Acoustic masking showed a reduced, but statistically significant effect of electric threshold elevation, which did not significantly depend on MPI. Lastly, acoustic masking showed longer decay times than electric masking and a reduced dependency on EAFD. In conclusion, the forward masking patterns observed for combined electric-acoustic stimulation provide further insights into the temporal mechanisms of the auditory system. For instance, the asymmetry in the amount of threshold elevation, the dependency on EAFD and the time constants for the recovery functions of acoustic and electric masking all indicate that there must be several processes with different latencies (e.g. neural adaptation, depression of spontaneous activity, efferent systems) that are involved in forward masking recovery functions.
为了研究听觉系统的时间机制，对患侧耳仍保留听觉的人工耳蜗使用者进行了心理物理学前掩蔽实验。这种独特的电声刺激（EAS）人群分别允许在存在电掩蔽器或声掩蔽器的情况下测量声探针或电探针的阈值恢复函数。在电掩蔽实验中，测量声探针的前掩蔽阈值升高作为电掩蔽器偏移后时间间隔的函数，即掩蔽器到探针间隔（MPI）。在声掩蔽实验中，研究了在前一个声掩蔽器影响下电探针刺激的前掩蔽阈值升高。由于电脉冲序列直接刺激听神经，这种新颖的实验设置使得能够将（归因于毛细胞生理学的）听觉适应特性与沿听觉通路的更中枢机制的后续处理区分开来。例如，前向电掩蔽模式应该更多地是听神经对电刺激的反应结果，而前向声掩蔽模式应该主要是毛细胞 - 神经元界面适应恢复的结果。电掩蔽显示出声探针的阈值升高持续时间延长，这显著取决于掩蔽器到探针的间隔。此外，阈值升高显著取决于声刺激频率与电位置频率之间的相似性，即电声频率差（EAFD）。声掩蔽显示电阈值升高的影响有所降低，但具有统计学意义，且该影响不显著依赖于MPI。最后，声掩蔽显示出比电掩蔽更长的衰减时间，并且对EAFD的依赖性降低。总之，观察到的联合电声刺激的前掩蔽模式为听觉系统的时间机制提供了进一步的见解。例如，阈值升高量的不对称性、对EAFD的依赖性以及声掩蔽和电掩蔽恢复函数的时间常数都表明，在前掩蔽恢复函数中必定涉及几个具有不同潜伏期的过程（例如神经适应、自发活动抑制、传出系统）。
