Individual differences in alpha frequency drive crossmodal illusory perception.
Bottom Line: Stimulus temporal proximity critically determines whether or not these inputs are bound together.Based on these observations, we hypothesized that the duration of each alpha cycle might provide the temporal unit to bind audio-visual events.Participants then performed the same task while receiving occipital transcranial alternating current stimulation (tACS), to modulate oscillatory activity either at their IAF or at off-peak alpha frequencies (IAF±2 Hz).
Affiliation: Centre for Brain Science, Department of Psychology, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK; Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, Glasgow G12 8QB, UK.Show MeSH
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Mentions: To assess the correlation between individual alpha frequency (IAF) peak and the width of the temporal window of integration in which the illusion is perceived, we tested 22 healthy volunteers using a paradigm adapted from Shams et al.  where two beeps (7 ms duration) were played at different time delays between 36–204 ms (12 ms steps; see Supplemental Information and Figure S1 available online). A white disk was flashed for 12 ms below a fixation point time-aligned to the first beep, and participants reported whether they perceived one or two flashes. A sigmoid function was fitted to individual observations (see behavioral data analysis in Supplemental Information) to determine the inflection point of each participant’s behavioral curve, providing a reliable estimate of the temporal window in which the illusion was maximally perceived (average ∼100 ms; Figure 1A). EEG activity was recorded during the task and fast Fourier transform (FFT) used to calculate individual alpha frequency (IAF) peaks across the entire electrode array (Figure 1B). Inflection point values were then correlated with the width of IAF cycles revealing that these two measures were strongly and positively correlated with maxima over occipital electrodes (O1, O2, and Oz; n = 22, r = 0.697, regression slope = 1.4, y intercept = 0.34, p < 0.001; see Figure 1C), in line with our hypothesis.
Affiliation: Centre for Brain Science, Department of Psychology, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK; Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, Glasgow G12 8QB, UK.