Shofner W P, Yost W A
Parmly Hearing Institute, Loyola University Chicago, IL 60626, USA. internet:
Hear Res. 1997 Aug;110(1-2):15-24. doi: 10.1016/s0378-5955(97)00063-4.
Iterated rippled noise having infinite iterations is generated when a flat-spectrum wideband noise is delayed T ms and the delayed version is added to the undelayed noise through positive feedback. The resulting signal has a rippled spectrum, and the perceived pitch of this iterated rippled noise by human listeners corresponds to a frequency of 1/T. We have previously demonstrated that chinchillas can discriminate the rippled-spectrum noise from the flat-spectrum noise. In the present study, chinchillas discriminated a bandpass filtered rippled-spectrum noise from a bandpass flat-spectrum noise in a psychophysical task. The passbands were set to be one octave wide. Psychometric functions were obtained for 5 chinchillas and performance was measured as d'. The best behavioral performance was obtained when the center frequency of the bandpass filter generally corresponded to the 3rd 5th harmonic peak of the rippled noise (i.e., at 3/T to 5/T), but the precise location of the dominant region varied with the delay of the rippled noise such that the dominance region tended to shift to lower harmonics as 1/T increased. These results indicate that not all spectral regions are weighted equally in the discrimination task. The spectral dominance region found in chinchillas is similar to that described for human pitch perception.
当一个平谱宽带噪声被延迟T毫秒，并且延迟后的版本通过正反馈加到未延迟的噪声上时，就会产生具有无限次迭代的迭代波纹噪声。产生的信号具有波纹状频谱，人类听众对这种迭代波纹噪声的感知音高对应于1/T的频率。我们之前已经证明，龙猫能够区分波纹状频谱噪声和平谱噪声。在本研究中，龙猫在一项心理物理学任务中区分了带通滤波后的波纹状频谱噪声和带通平谱噪声。通带设置为一个八度宽。为5只龙猫获得了心理测量函数，并将表现测量为d'。当带通滤波器的中心频率通常对应于波纹噪声的第3至第5谐波峰值时（即3/T至5/T），获得了最佳行为表现，但主导区域的精确位置随波纹噪声的延迟而变化，使得主导区域倾向于随着1/T的增加而向较低谐波移动。这些结果表明，在辨别任务中并非所有频谱区域都被同等加权。在龙猫中发现的频谱主导区域与人类音高感知中描述的相似。
