Research Center for Science and Technology, Tokyo Denki University, Inzai, Japan.
PLoS One. 2013 Sep 23;8(9):e75990. doi: 10.1371/journal.pone.0075990. eCollection 2013.
The auditory illusory perception "scale illusion" occurs when a tone of ascending scale is presented in one ear, a tone of descending scale is presented simultaneously in the other ear, and vice versa. Most listeners hear illusory percepts of smooth pitch contours of the higher half of the scale in the right ear and the lower half in the left ear. Little is known about neural processes underlying the scale illusion. In this magnetoencephalographic study, we recorded steady-state responses to amplitude-modulated short tones having illusion-inducing pitch sequences, where the sound level of the modulated tones was manipulated to decrease monotonically with increase in pitch. The steady-state responses were decomposed into right- and left-sound components by means of separate modulation frequencies. It was found that the time course of the magnitude of response components of illusion-perceiving listeners was significantly correlated with smooth pitch contour of illusory percepts and that the time course of response components of stimulus-perceiving listeners was significantly correlated with discontinuous pitch contour of stimulus percepts in addition to the contour of illusory percepts. The results suggest that the percept of illusory pitch sequence was represented in the neural activity in or near the primary auditory cortex, i.e., the site of generation of auditory steady-state response, and that perception of scale illusion is maintained by automatic low-level processing.
当一个上升音阶的音调在一只耳朵中呈现，同时另一只耳朵中呈现一个下降音阶的音调，反之亦然，就会出现听觉幻觉“音阶错觉”。大多数听众在右耳听到音阶的较高半部分的平滑音高轮廓的幻觉，而在左耳听到音阶的较低半部分的幻觉。对于音阶错觉背后的神经过程知之甚少。在这项脑磁图研究中，我们记录了对具有诱导音高序列的调制短音的稳态响应，其中调制音的声级随着音高的增加而单调下降。通过单独的调制频率，将稳态响应分解为右音和左音分量。结果发现，幻觉感知者的响应分量的大小的时间历程与幻觉感知的平滑音高轮廓显著相关，而刺激感知者的响应分量的时间历程与刺激感知的不连续音高轮廓显著相关，除了幻觉感知的轮廓之外。结果表明，幻觉音高序列的感知是在初级听觉皮层或其附近的神经活动中表示的，即听觉稳态响应的产生部位，并且音阶错觉的感知是通过自动的低水平处理来维持的。
