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: It could be argued that present effects of tACS could be alternatively explained by shifts in the overall illusion susceptibility by tACS at IAF−2 Hz rather than our more specific windowing hypothesis. We reasoned that if these findings are the result of a general increase in the likelihood of the illusion at lower alpha frequency, then a differential probability of illusion between the ±2 Hz (i.e., the most extreme) conditions would be expected irrespective of the interbeep interval, i.e., not only around the inflection points but also at very short and very long stimulus onset asynchronies (SOAs). Alternatively, if the effect is determined by tACS windowing action, we would specifically predict a significant change in the probability of illusion only around the inflection points but not at the extreme interbeep intervals. We tested these two hypotheses using paired t tests to compare the probability of illusion between the ±2 Hz conditions at each interbeep interval. The results (see Figure 3) showed that the probability of illusion between ±2 Hz only differed at interbeep intervals around the inflection points (i.e., 100 ms). Specifically, 108 ms interbeep interval showed a significant difference between ±2 Hz (t(11) = 4.4, p = 0.015, one-tailed, Bonferroni corrected for 15 comparisons), whereas 96 ms interbeep interval showed a trend for a significant difference (t(11) = 2.98, p = 0.09, one-tailed, Bonferroni corrected). Crucially, the probability of illusion at all the other interbeep intervals did not change between ±2 Hz conditions (all t values <2.4, all p values >0.23, one-tailed, Bonferroni corrected).
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.