Leibniz Institute for Neurobiology, 39118 Magdeburg, Germany.
Hear Res. 2012 Dec;294(1-2):133-42. doi: 10.1016/j.heares.2012.08.014. Epub 2012 Sep 16.
Perceptually ambiguous stimuli are useful for testing psychological and neuronal models of perceptual organization, e.g. for studying brain processes that underlie sequential segregation and integration. This is because the same stimuli may give rise to different subjective experiences. For humans, a tone sequence that alternates between a low-frequency and a high-frequency tone is perceptually bistable, and can be perceived as one or two streams. In the current study we present a new method based on response times (RTs) which allows identification ambiguous and unambiguous stimuli for subjects who cannot verbally report their subjective experience. We required two macaque monkeys (macaca fascicularis) to detect the termination of a sequence of light flashes which were either presented alone, or synchronized in different ways with a sequence of alternating low and high tones. We found that the monkeys responded faster to the termination of the flash sequence when the tone sequence terminated shortly before the flash sequence and thus predicted the termination of the flash sequence. This RT gain depended on the frequency separation of the tones. RT gains were largest when the frequency separation was small and the tones were presumably heard mainly as one stream. RT gains were smallest when the frequency separation was large and the tones were presumably mainly heard as two streams. RT gain was of intermediate size for intermediate frequency separations. Similar results were obtained from human subjects. We conclude that the observed RT gains reflect the perceptual organization of the tone sequence, and that tone sequences with an intermediate frequency separation, as for humans, are perceptually ambiguous for monkeys.
感知上模棱两可的刺激对于测试感知组织的心理和神经元模型很有用，例如用于研究支持序列分离和整合的大脑过程。这是因为相同的刺激可能会产生不同的主观体验。对于人类来说，低频和高频音交替出现的音调序列在感知上是双稳态的，可以被感知为一个或两个音流。在当前的研究中，我们提出了一种基于反应时间（RT）的新方法，该方法允许为无法口头报告其主观体验的受试者识别模棱两可和非模棱两可的刺激。我们要求两只猕猴（猕猴）检测光闪烁序列的终止，这些光闪烁要么单独呈现，要么与交替的低和高音序列以不同的方式同步呈现。我们发现，当音调序列在光闪烁序列之前不久终止时，猴子对光闪烁序列的终止反应更快，从而预测了光闪烁序列的终止。这种 RT 增益取决于音调的频率分离。当频率分离较小时，音调可能主要被听到为一个音流，因此 RT 增益最大。当频率分离较大且音调主要被听到为两个音流时，RT 增益最小。当频率分离处于中间时，RT 增益处于中间大小。人类受试者也得到了类似的结果。我们得出的结论是，观察到的 RT 增益反映了音调序列的感知组织，并且对于猴子来说，具有中间频率分离的音调序列在感知上是模棱两可的，就像人类一样。
