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Pre-stimulus beta-band oscillations influence the perception of the sound induced flash illusion
Julian Keil, Nathan Weisz
Recent studies have reported on the influence of pre-stimulus oscillatory brain activity on multimodal perception. In a previous study using the McGurk illusion, we found that varying perception upon invariant stimulation is preceded by modulations in local beta band power in the left superior temporal gyrus and phase locking to frontal and temporal areas. As this illusion uses complex visual and
auditory stimuli, we used the simpler Sound Induced Flash Illusion (SIFI) paradigm to elucidate the basic processes associated with modulations of multimodal perception.
Stimuli:
* 600 Trials in 4 blocks of 150 trials, 390 critical trials (1 dot, 2 tones) * Response on the perceived number of dots via response pad
Recording:
* 148-Channel MEG system (MAGNES™ 2500 WH, 4D Neuroimaging, San Diego, USA)
* 678.17 Hz Sample rate, 0.1-200 Hz Online band pass filter Analysis:
* Segmentation in 4 second trials around stimulus onset * Visual artifact rejection, 1 Hz Offline high pass filter
* Morlet wavelet time-frequency analysis between 5 and 90 Hz
* Dependent-samples T-Test with Monte-Carlo randomization and cluster-based correction for multiple comparisons (-0.5 s to 0.5 s. 5 to 40 Hz)
* Adaptive linear spatial filtering (DICS) source analysis
* Phase-locking value between regions of interest from source analysis and whole brain volume between 5 and 40 Hz.
We show that multisensory integration critically depends on local brain activity and the functional state of information processing
networks, thus replicating and extending work from our own lab and others. Fluctuating integration of multisensory areas with primary sensory and higher-order areas forms predispositions whether different sensory streams will be integrated or not. This predisposition appears to be more important than the actual processes elicited by the delivery of the stimuli.
Supported by the DFG (Deutsche Forschungsgemeinschaft) and Zukunftskolleg of the University of Konstanz.
We thank Stefanie Franzkowiak, Nadia Müller, Thomas Hartmann, Hannah Schulz, Sabine Jatzev and Teresa Übelacker References:
Fieldtrip Matlab-toolbox: http://fieldtrip.fcdonders.nl/
Shams et al. (2000), What you see is what you hear. Nature, 408, 788. | Shams et al. (2002), Visual illusions induced by sound.
Cognitive Brain Research, 14, 147-152.
Contact: julian.keil@uni-konstanz.de | www.uni-konstanz.de/obob | P.O. Box D25 78457 Konstanz, Germany | 0049 (0)7531 88 42 50
IntroductionMethodsResultsConclusionsReferences
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Proportion of Trials
-0.5 -0.4 -0.3 -0.2 -0.1 0
5 10 15 20 25 30 35 40
time (s)
Frequency (Hz)
-3 -2 -1 0 1 2 3
t-values
-4 -3 -2 -1 0 1 2 3 4
t-values
BA39 BA44 BA21
BA18
A1
V1 MFG
BA4
BA39 : BA21 | BA18
V1 : BA44 V1 : BA4 V1 : MFG
rA1 : BA18
-3 -2 -1 0 1 2 3
t-values
-4 -3 -2 -1 0 1 2 3 4
t-values
We compared the time-frequency representation of trials containing the SIFI (i.e. perception of two discs) with trials without the illusory percept (i.e. perception of one disc). Before the stimulus onset (-0.5 s to -0.1 s), beta band (13 - 21 Hz) power increased (p < 0.05)
when subjects subsequently reported the illusion (above left). The magnetometer topography indicated a left temporal source for this effect. The source analysis localized it in the left middle temporal gyrus (BA39, above middle). We projected the MEG data into source space and computed phase locking values between the regions of interest (BA39, primary visual and auditory regions) and the whole brain volume. In the comparison of illusion trials versus non-illusion trials in this time window, BA39 was functionally coupled to left
temporal areas (BA21) and decoupled from occipital areas (BA18) in the beta band (13 - 21 Hz, above left, dashed lines). In the alpha band (9 - 11 Hz, above left, solid lines), primary auditory cortex was functionally coupled to occipital areas (BA18). Primary visual
cortex was coupled to medial frontal (MFG) and parietal (BA4) areas and decoupled from inferior frontal areas (BA44).
Konstanzer Online-Publikations-System (KOPS) URN: http://nbn-resolving.de/urn:nbn:de:bsz:352-163423
