Finneran James J, Echon Roxanne, Mulsow Jason, Houser Dorian S
U.S. Navy Marine Mammal Program, Space and Naval Warfare Systems Center Pacific, Code 71510, 53560 Hull Street, San Diego, California 92152, USA.
National Marine Mammal Foundation, 2240 Shelter Island Drive, #200, San Diego, California 92106, USA.
J Acoust Soc Am. 2016 Jul;140(1):296. doi: 10.1121/1.4955093.
Biosonar gain control mechanisms in a bottlenose dolphin were investigated by measuring the auditory steady-state response (ASSR) to an external tone while the animal echolocated. The dolphin performed an echo change-detection task that utilized electronically synthesized echoes with echo delays corresponding to 25- and 50-m target range. During the task, amplitude modulated tones with carrier frequencies from 25 to 125 kHz were continuously presented and the instantaneous electroencephalogram stored for later analysis. ASSRs were extracted from the electroencephalogram by synchronously averaging time epochs temporally aligned with the onset of the external tone modulation cycle nearest to each of the dolphin's echolocation clicks. Results showed an overall suppression of the ASSR amplitude for tones with frequencies near the click center frequencies. A larger, temporary suppression of the ASSR amplitude was also measured at frequencies above 40-50 kHz, while a temporary enhancement was observed at lower frequencies. Temporal patterns for ASSR enhancement or suppression were frequency-, level-, and range-dependent, with recovery to pre-click values occurring within the two-way travel time. Suppressive effects fit the patterns expected from forward masking by the emitted biosonar pulse, while the specific mechanisms responsible for the frequency-dependent enhancement are unknown.
通过在宽吻海豚进行回声定位时测量其对外部音调的听觉稳态反应（ASSR），研究了宽吻海豚的生物声纳增益控制机制。海豚执行了一项回声变化检测任务，该任务利用电子合成的回声，其回声延迟对应于25米和50米的目标距离。在任务过程中，持续呈现载波频率为25至125千赫兹的调幅音调，并存储瞬时脑电图以供后续分析。通过对与最接近海豚每次回声定位点击的外部音调调制周期开始时间在时间上对齐的时间片段进行同步平均，从脑电图中提取ASSR。结果表明，对于频率接近点击中心频率的音调，ASSR幅度总体上受到抑制。在40 - 50千赫兹以上的频率处，还测量到ASSR幅度更大的临时抑制，而在较低频率处观察到临时增强。ASSR增强或抑制的时间模式与频率、声级和距离有关，在双向传播时间内恢复到点击前的值。抑制效应符合由发出的生物声纳脉冲产生的前向掩蔽所预期的模式，而导致频率依赖性增强的具体机制尚不清楚。
