Farris Hamilton E, Hoy Ronald R
Department of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853, USA.
J Acoust Soc Am. 2002 Mar;111(3):1475-85. doi: 10.1121/1.1451069.
Sounds with frequencies >15 kHz elicit an acoustic startle response (ASR) in flying crickets (Eunemobius carolinus). Although frequencies <15 kHz do not elicit the ASR when presented alone, when presented with ultrasound (40 kHz), low-frequency stimuli suppress the ultrasound-induced startle. Thus, using methods similar to those in masking experiments, we used two-tone suppression to assay sensitivity to frequencies in the audio band. Startle suppression was tuned to frequencies near 5 kHz, the frequency range of male calling songs. Similar to equal loudness contours measured in humans, however, equal suppression contours were not parallel, as the equivalent rectangular bandwidth of suppression tuning changed with increases in ultrasound intensity. Temporal integration of suppressor stimuli was measured using nonsimultaneous presentations of 5-ms pulses of 6 and 40 kHz. We found that no suppression occurs when the suppressing tone is >2 ms after and >5 ms before the ultrasound stimulus, suggesting that stimulus overlap is a requirement for suppression. When considered together with our finding that the intensity of low-frequency stimuli required for suppression is greater than that produced by singing males, the overlap requirement suggests that two-tone suppression functions to limit the ASR to sounds containing only ultrasound and not to broadband sounds that span the audio and ultrasound range.
频率大于15千赫兹的声音会引发卡罗莱纳安乐螽斯飞行时的听觉惊吓反应（ASR）。虽然单独呈现频率小于15千赫兹的声音时不会引发听觉惊吓反应，但当与超声波（40千赫兹）同时呈现时，低频刺激会抑制超声波诱发的惊吓反应。因此，我们采用类似于掩蔽实验的方法，利用双音抑制来测定对音频频段频率的敏感度。惊吓抑制作用会调谐到接近5千赫兹的频率，即雄性求偶鸣叫的频率范围。然而，与在人类中测量的等响度轮廓类似，等抑制轮廓并不平行，因为抑制调谐的等效矩形带宽会随着超声波强度的增加而变化。使用6千赫兹和40千赫兹的5毫秒脉冲非同时呈现来测量抑制刺激的时间整合。我们发现，当抑制音在超声波刺激之后大于2毫秒且在超声波刺激之前大于5毫秒时，不会发生抑制作用，这表明刺激重叠是抑制作用的一个必要条件。结合我们的发现，即抑制所需的低频刺激强度大于鸣叫雄性产生的强度，重叠要求表明双音抑制的作用是将听觉惊吓反应限制在仅包含超声波的声音上，而不是跨越音频和超声波范围的宽带声音上。
