Department of Psychology, University of Milano-Bicocca, Piazza dell'Ateneo Nuovo 1, 20126, Milan, Italy,
Exp Brain Res. 2013 Dec;231(4):469-78. doi: 10.1007/s00221-013-3711-1. Epub 2013 Oct 4.
Crossmodal illusions clearly show how perception, rather than being a modular and self-contained function, can be dramatically altered by interactions between senses. Here, we provide evidence for a novel crossmodal "physiological" illusion, showing that sounds can boost visual cortical responses in such a way to give rise to a striking illusory visual percept. In healthy participants, a single-pulse transcranial magnetic stimulation (sTMS) delivered to the occipital cortex evoked a visual percept, i.e., a phosphene. When sTMS is accompanied by two auditory beeps, the second beep induces in neurologically unimpaired participants the perception of an illusory second phosphene, namely the sound-induced phosphene illusion. This perceptual "fission" of a single phosphene, due to multiple beeps, is not matched by a "fusion" of double phosphenes due to a single beep, and it is characterized by an early auditory modulation of the TMS-induced visual responses (~80 ms). Multiple beeps also induce an illusory feeling of multiple TMS pulses on the participants' scalp, consistent with an audio-tactile fission illusion. In conclusion, an auditory stimulation may bring about a phenomenological change in the conscious visual experience produced by the transcranial stimulation of the occipital cortex, which reveals crossmodal binding mechanisms within early stages of visual processing.
跨模态错觉清楚地表明，感知不是一个模块化和自成一体的功能，而是可以通过感官之间的相互作用而发生显著改变。在这里，我们提供了一种新的跨模态“生理”错觉的证据，表明声音可以以这样的方式增强视觉皮层反应，从而产生引人注目的错觉视觉感知。在健康参与者中，单个脉冲经颅磁刺激（sTMS）施加于枕叶皮层会引起视觉感知，即光幻视。当 sTMS 伴随着两个听觉哔哔声时，第二个哔哔声会在神经功能未受损的参与者中引起第二个光幻视的感知，即声音引起的光幻视错觉。由于多个哔哔声，单个光幻视的这种感知“分裂”，与由于单个哔哔声引起的双光幻视的“融合”不匹配，并且其特征在于 TMS 诱导的视觉响应的早期听觉调制（约 80ms）。多个哔哔声也会在参与者的头皮上引起多个 TMS 脉冲的错觉感觉，与音频触觉分裂错觉一致。总之，听觉刺激可能会引起由枕叶皮层经颅刺激产生的有意识视觉体验的现象学变化，这揭示了视觉加工早期阶段的跨模态绑定机制。
