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: In a second experiment, we sought causal evidence for a link between individual differences in IAF and the temporal window of the double-flash illusion. In 12 participants, we now delivered transcranial alternating current stimulation (tACS) over occipital cortex to modulate occipital oscillations  at their IAF or at slower (IAF−2 Hz) or faster (IAF+2 Hz) frequencies, i.e., far from IAF but still within the alpha band, while they were performing the flash-beep task (see Figure S2). If IAF causally determines the individual window of illusion (i.e., the inflection point of the sigmoid), then we hypothesized that driving IAF toward slower versus faster oscillations should result in wider versus shorter windows of illusion, respectively. Consistent with this hypothesis, repeated-measures ANOVA on inflection points (in ms) showed a main effect of tACS condition (F(2,22) = 10.11, p < 0.001, Figure 2). Post hoc paired t tests revealed that occipital tACS at IAF+2 Hz (92.7 ± 7.9 ms) significantly shrunk (t(11) = 1.82, p < 0.05, one-tailed), whereas IAF−2 Hz (106.4 ± 8.7 ms) significantly expanded (t(11) = 2.7, p = 0.01, one-tailed) the temporal window of the illusion relative to tACS at IAF (97.9 ± 7.6 ms) and relative to each other (t(11) = 4.29, p < 0.001, one-tailed). These tACS-dependent shifts in opposite directions suggest that IAF causally determines the temporal window of illusion.
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.