ABSTRACT Auditory adaptation manifests as temporary change in the hearing sensitivity under influence of sound stimuli, and little attention has been paid to hearing adaptation in cetaceans. In a Yangtze finless porpoise Neophocaena asiaeorientalis (Cetacea, Phocoenidae), effects of long-lasting sound stimuli (pip trains) on auditory evoked potentials (AEP) were investigated. The stimuli were rhythmic tone pips of either 90 or 128 kHz frequency. Stimulus levels varied from 80 to 120 dB re 1 μPa. During stimulation, the stimulus level was either kept constant the stimulus level changed up and down by 20 or 40 dB every 1000 ms. A stimulus level increase produced quick response amplitude increase with subsequent slower exponential decay; the exponent time constant was 59.2 ± 9.7 ms. A stimulus level decrease produced quick response amplitude suppression with subsequent exponent recovery; the exponent time constant was 153.9 ± 15.9 ms. The response variations were assessed as manifestations of adaptation processes. The finless porpoise is capable of quickly adjusting its sensitivity to the current auditory scene. This flexibility allows for quick sensitivity recovery after exposure to loud noises and is important for the effective use of auditory orientation. Abbreviations: RFR: rate-following response; AEP: auditory evoked potentials; A/D: analogue-to-digital (A/D); ERD: equivalent rectangular duration

中文翻译：

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长江江豚听觉适应时程，Neophocaena asiaeorientalis asiaeorientalis

摘要 听觉适应表现为在声音刺激作用下听觉灵敏度的暂时性变化，而鲸类动物的听觉适应很少受到关注。在长江江豚 Neophocaena asiaeorientalis（鲸目、Phocoenidae）中，研究了持久声音刺激（pip trains）对听觉诱发电位 (AEP) 的影响。刺激是 90 或 128 kHz 频率的有节奏的音调。刺激水平从 80 到 120 dB re 1 μPa 不等。在刺激期间，刺激水平要么保持恒定，刺激水平每 1000 ms 上下变化 20 或 40 dB。刺激水平增加产生快速响应幅度增加，随后指数衰减较慢；指数时间常数为 59.2 ± 9.7 ms。刺激水平降低产生快速响应幅度抑制，随后指数恢复；指数时间常数为 153.9 ± 15.9 ms。反应变化被评估为适应过程的表现。江豚能够快速调整其对当前听觉场景的敏感度。这种灵活性允许在暴露于嘈杂的噪音后快速恢复灵敏度，并且对于有效使用听觉定向很重要。缩写： RFR：速率跟随响应；AEP：听觉诱发电位；A/D：模数（A/D）；ERD：等效矩形持续时间 江豚能够快速调整其对当前听觉场景的敏感度。这种灵活性允许在暴露于嘈杂的噪音后快速恢复灵敏度，并且对于有效使用听觉定向很重要。缩写： RFR：速率跟随响应；AEP：听觉诱发电位；A/D：模数（A/D）；ERD：等效矩形持续时间 江豚能够快速调整其对当前听觉场景的敏感度。这种灵活性允许在暴露于嘈杂的噪音后快速恢复灵敏度，并且对于有效使用听觉定向很重要。缩写： RFR：速率跟随响应；AEP：听觉诱发电位；A/D：模数（A/D）；ERD：等效矩形持续时间