Ghazanfar Asif A, Maier Joost X
Neuroscience Institute, Department of Psychology, Green Hall, Princeton University, Princeton, NJ 08540, USA.
Behav Neurosci. 2009 Aug;123(4):822-7. doi: 10.1037/a0016391.
Rising sound intensity provides an important cue for the detection of looming objects. Studies with humans indirectly suggest that rising pitch can also signal a looming object. This link between rising intensity and rising frequency is puzzling because no physical rise in frequency occurs when a sound source approaches. Putative explanations include (a) the idea that the loudness of sound depends on its frequency, (b) the frequent co-occurrence of rising intensity with rising frequency in vocalizations generates an association between the 2 features, and (c) auditory neurons process amplitude- and frequency-modulated sounds similarly. If these hypotheses are valid, then rhesus monkeys (Macaca mulatta)--which share some homologies in the vocal production apparatus and auditory system--should also associate rising frequency with rising intensity, and thus should perceive rising frequency as a looming sound source. A head-turning assay and a preferential-looking paradigm revealed that monkeys show an attentional bias toward rising versus falling frequency sounds and link the former to visual looming signals. This suggests that monkeys hear a rising frequency sound as a looming sound source even though, in the real world, no such link exists.
声音强度的增加为检测逼近物体提供了重要线索。对人类的研究间接表明，音高的升高也可以表明有物体在逼近。强度增加与频率升高之间的这种联系令人困惑，因为当声源靠近时，频率并没有实际升高。可能的解释包括：（a）声音的响度取决于其频率；（b）发声中强度增加与频率升高经常同时出现，从而在这两个特征之间产生了关联；（c）听觉神经元对幅度调制和频率调制声音的处理方式相似。如果这些假设成立，那么在发声器官和听觉系统上有一些同源性的恒河猴也应该将频率升高与强度增加联系起来，从而将频率升高视为逼近的声源。一项转头试验和一种优先注视范式表明，猴子对频率升高的声音与频率降低的声音表现出注意力偏向，并将前者与视觉上的逼近信号联系起来。这表明，即使在现实世界中不存在这样的联系，猴子也会将频率升高的声音听成逼近的声源。
