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Pre- and post-stimulus EEG patterns associated with the touch-induced illusory flash

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Author: Erp, J.B.F. van · Philippi, T.G. · Winkel, K.N. de · Werkhoven, P.
Source:Neuroscience Letters, 562, 79-84
Identifier: 489158
doi: doi:10.1016/j.neulet.2014.01.010
Keywords: Perception · Alpha · EEG · Illusion · Illusory flash · Multisensory · Pre-stimulus · Human Performances · PCS - Perceptual and Cognitive Systems · ELSS - Earth, Life and Social Sciences


Pairing two brief auditory beeps with a single flash can evoke the percept of a second, illusory, flash. Investigations of the underlying neural mechanisms are limited to post-stimulus effects of this sound-induced illusory flash. We investigated whether touch modulates the visual evoked potential in a similar vein, and also looked at pre-stimulus activity. Electroencephalogram (EEG) was recorded over occipital and parieto-occipital areas of 12 observers. We compared bimodal EEG to its unimodal constituents (i.e., the difference waves) and found significant positive deflections around 110. ms and 200. ms and negative deflections around 330. ms and 390. ms from stimulus onset. These results are similar to those reported for the sound-induced illusion, albeit somewhat later. Furthermore, comparison of the EEG activity between those trials in which the illusion was perceived and those in which it was absent revealed that the phase of pre-stimulus alpha was linked to perceiving the illusion or not. We conclude that touch can modulate activity in the visual cortex and that similar neural mechanisms underlie perception of the sound- and touch-induced illusory flash and that the phase of the alpha wave at the moment of presentation that affects perception. © 2014 Elsevier Ireland Ltd.