Biological Psychology and Neuropsychology, University of Hamburg, Hamburg, Germany.
J Cogn Neurosci. 2009 Dec;21(12):2445-61. doi: 10.1162/jocn.2008.21177.
When a single tactile stimulus is presented together with two tones, participants often report perceiving two touches. It is a matter of debate whether this cross-modal effect of audition on touch reflects the interplay between modalities at early perceptual or at later processing stages, and which brain processes determine what in the end is consciously perceived. Event-related brain potentials (ERPs) were recorded while rare single tactile stimuli accompanied by two tones (1T2A) were presented among frequent tactile double stimuli accompanied by two tones (2T2A). Although participants were instructed to ignore the tones and to respond to single tactile stimuli only, they often failed to respond to 1T2A stimuli ("illusory double touches," 1T2A(i)). ERPs to "illusory double touches" versus "real double touches" (2T2A) differed 50 msec after the (missing) second touch. This suggests that at an early sensory stage, illusory and real touches are processed differently. On the other hand, although similar stimuli elicited a tactile mismatch negativity (MMN) between 100 and 200 msec in a unisensory tactile experiment, no MMN was observed for the 1T2A(i) stimuli in the multisensory experiment. "Tactile awareness" was associated with a negativity at 250 msec, which was enhanced in response to correctly identified deviants as compared to physically identical deviants that elicited an illusion. Thus, auditory stimuli seem to alter neural mechanisms associated with automatic tactile deviant detection. The present findings contribute to the debate of which processing step in the brain determines what is consciously perceived.
当单一触觉刺激与两个音调同时呈现时，参与者通常会报告感觉到两个触感。一个有争议的问题是，听觉对触觉的这种跨模态效应是反映了模态在早期知觉阶段还是在后期加工阶段的相互作用，以及哪些大脑过程决定了最终被有意识地感知到的内容。当罕见的单个触觉刺激伴随着两个音调（1T2A）与频繁的两个音调伴随的两个触觉刺激（2T2A）一起呈现时，记录了事件相关脑电位（ERPs）。尽管参与者被指示忽略音调并仅对单个触觉刺激做出反应，但他们经常未能对 1T2A 刺激做出反应（“错觉双重触感”，1T2A(i)）。与“真实双重触感”（2T2A）相比，“错觉双重触感”的 ERPs 在（缺失的）第二个触感后 50 毫秒处有所不同。这表明在早期感觉阶段，错觉和真实触感的处理方式不同。另一方面，尽管在单感觉触觉实验中，类似的刺激在 100 到 200 毫秒之间引发了触觉失匹配负波（MMN），但在多感觉实验中，对于 1T2A(i)刺激，并未观察到 MMN。“触觉意识”与 250 毫秒处的负性相关，与引发错觉的物理上相同的偏差相比，正确识别偏差时会增强这种负性。因此，听觉刺激似乎改变了与自动触觉偏差检测相关的神经机制。本研究结果有助于解决大脑中哪个加工步骤决定了什么是被有意识地感知到的问题。
