Pfingst B E, Rai D T
Kresge Hearing Research Institute, Department of Otolaryngology, University of Michigan Medical Center, Ann Arbor 48109-0506.
Hear Res. 1990 Dec;50(1-2):43-56. doi: 10.1016/0378-5955(90)90032-k.
The purpose of this experiment was to study the effects of stimulus level on discrimination of frequency as represented in the temporal waveforms of acoustic and electrical signals. The subjects were four nonhuman primates in which one ear had been deafened and implanted with an electrode array and the other ear was untreated. Frequency difference limens for 100 Hz electrical sinusoidal stimulation via a cochlear implant in the deafened ear were compared to those for 100 Hz sinusoidally amplitude-modulated white noise (SAM noise) acoustic stimuli to the normal-hearing contralateral ear. To correct for loudness cues, levels of the test stimuli were varied relative to the reference-stimulus level. The test-stimulus levels at which the percent responses were minimum were determined. These levels were used to measure the frequency difference limens. Frequency difference limens for the electrical stimuli decreased as a function of reference-stimulus level through most of the dynamic range, while those for the acoustic stimuli reached a minimum at 20 dB to 40 dB above threshold. For the electrical stimuli the slopes and relative positions of the frequency difference limen vs. level functions varied from subject to subject, and with changes in electrode configuration within a subject. These differences were related to threshold level and dynamic range. At higher levels of stimulation, frequency difference limens for acoustic and electrical stimuli fell in the same range. The slopes and relative positions of the frequency difference limen vs. level functions for electrical stimuli did not parallel those of level difference limen vs. level functions collected simultaneously from the same ears. The data suggest that nonspectral frequency discrimination may depend on the number of nerve fibers stimulated. With prostheses in cochleas with less than a full complement of auditory nerve fibers, the data suggest that stimulation level is an important variable influencing discriminability.
本实验的目的是研究刺激水平对频率辨别能力的影响，这种影响通过声学和电信号的时间波形来体现。实验对象是四只非人灵长类动物，其中一只耳朵致聋并植入了电极阵列，另一只耳朵未作处理。将通过人工耳蜗对致聋耳朵进行的100Hz电正弦刺激的频率辨别阈，与对正常听力的对侧耳朵进行的100Hz正弦调幅白噪声（SAM噪声）声学刺激的频率辨别阈进行比较。为校正响度线索，测试刺激的水平相对于参考刺激水平而变化。确定了反应百分比最小的测试刺激水平。这些水平用于测量频率辨别阈。在大部分动态范围内，电刺激的频率辨别阈随参考刺激水平的变化而降低，而声学刺激的频率辨别阈在高于阈值20dB至40dB时达到最小值。对于电刺激，频率辨别阈与水平函数的斜率和相对位置因个体而异，并且在个体内随着电极配置的变化而变化。这些差异与阈值水平和动态范围有关。在较高刺激水平下，声学和电刺激的频率辨别阈落在相同范围内。电刺激的频率辨别阈与水平函数的斜率和相对位置，与从同一只耳朵同时收集的水平辨别阈与水平函数的斜率和相对位置并不平行。数据表明，非频谱频率辨别可能取决于被刺激的神经纤维数量。对于听觉神经纤维数量不足的耳蜗中的假体，数据表明刺激水平是影响辨别能力的一个重要变量。
