Cebulla Mario, Elberling Claus
ENT Clinic, Julius Maximilian-University, Würzburg, Germany.
J Am Acad Audiol. 2010 Jul-Aug;21(7):452-60. doi: 10.3766/jaaa.21.7.4.
A cochlear delay model has previously been proposed for the construction of a chirp stimulus in order to compensate for the temporal dispersion in the auditory periphery. The large intersubject variability in the model data suggests that a chirp constructed from the average model data will not be able to compensate equally well for the temporal dispersion in all normal-hearing subjects. For the recording of the auditory brain stem response (ABR), it has been suggested that the most efficient chirp for generating the largest response amplitude changes in duration with level, indicating that the delay model exhibits a latency change with frequency, which becomes larger at lower levels.
To investigate in normal-hearing subjects how the ABR varies in response to five different chirps and to study how the efficiency of each chirp changes with stimulus level.
A click and five chirps of different durations and constructed from the proposed delay model were designed with identical amplitude spectra. The six stimuli were used to record the ABR from 50 normal-hearing test subjects using a quasi-simultaneous stimulation technique at 50 and 30 dB nHL. The ABR recordings were evaluated by the peak-to-trough amplitude and the peak latency.
For the test group the following level effect was demonstrated: at 50 dB nHL the largest response amplitude was provided by a shorter chirp, whereas at 30 dB nHL the largest response amplitude was provided by a longer chirp. There is, however, large variability as to which of the five chirps generated the largest response in each individual subject, but at the two levels of stimulation, the best chirps were significantly correlated across the test group. All five chirps generated significantly larger ABRs than the click, but at 30 dB nHL the gain in response amplitude by using the chirps instead of the click was larger than at 50 dB nHL.
A chirp that evokes the largest broadband ABRs in normal-hearing subjects changes in duration with level-that is, being relatively short at higher levels (50 dB nHL) and relatively long at lower levels and near the threshold. However, the changes in amplitude in response to chirps of different durations are not very large, and it is therefore uncertain whether the outcome from using such chirps actually would outweigh the instrumental complexity of implementation. It appears that the largest advantage of using the chirp over the click is found at the lower levels of stimulation.
先前已提出一种耳蜗延迟模型，用于构建线性调频脉冲刺激，以补偿听觉外周的时间弥散。模型数据中受试者间的巨大变异性表明，由平均模型数据构建的线性调频脉冲无法同等有效地补偿所有正常听力受试者的时间弥散。对于听觉脑干反应（ABR）的记录，有人提出，产生最大反应幅度的最有效线性调频脉冲在持续时间上会随声级变化，这表明延迟模型的潜伏期随频率变化，在较低声级时变化更大。
研究正常听力受试者中ABR对五种不同线性调频脉冲的反应如何变化，并研究每种线性调频脉冲的效率如何随刺激声级变化。
设计了一个短声和由所提出的延迟模型构建的五种不同持续时间且具有相同幅度谱的线性调频脉冲。使用准同时刺激技术，在50和30 dB nHL下，用这六种刺激记录50名正常听力测试受试者的ABR。通过峰谷幅度和峰潜伏期对ABR记录进行评估。
对于测试组，证明了以下声级效应：在50 dB nHL时，较短的线性调频脉冲提供最大的反应幅度，而在30 dB nHL时，较长的线性调频脉冲提供最大的反应幅度。然而，在每个个体受试者中，五种线性调频脉冲中哪一种产生最大反应存在很大变异性，但在两个刺激声级下，测试组中最佳的线性调频脉冲具有显著相关性。所有五种线性调频脉冲产生的ABR均明显大于短声，但在30 dB nHL时，使用线性调频脉冲而非短声时反应幅度的增益大于在50 dB nHL时。
在正常听力受试者中，能诱发最大宽带ABR的线性调频脉冲在持续时间上随声级变化，即在较高声级（50 dB nHL）时相对较短，在较低声级及接近阈值时相对较长。然而，对不同持续时间的线性调频脉冲的反应幅度变化不是很大，因此使用此类线性调频脉冲的结果是否实际上会超过实施的仪器复杂性尚不确定。似乎使用线性调频脉冲相对于短声的最大优势在较低刺激声级时发现。
