Attentional inhibition by alpha power is modulated by faster theta rhythm and audio-visual congruency during natural speech perception

Audio-visual speech processing is a fundamental aspect of human communication; however, the neural oscillatory mechanisms, particularly those involving alpha rhythms, that underlie attention in tasks requiring attention and suppression remain unclear. To investigate this, we employed a complex audiovisual paradigm designed to explore how alpha rhythms, along with slower frequencies, monitor and integrate audio-visual information under congruent and incongruent conditions. Participants were presented with a TED Talk video while listening to auditory stimuli under four conditions: (1) congruent audio delivered to both ears, (2) congruent audio in one ear and incongruent audio in the other, with attention directed toward the congruent audio, (3) congruent audio in one ear and incongruent audio in the other, with attention directed toward the incongruent audio and (4) all-incongruent stimulus. To examine lateralized attention effects, participants were divided into left-attending and right-attending groups across individuals. By analysing fluctuations in alpha power with regards to audio-visual congruency and the side of attention, we observed a notable finding: alpha power fluctuations falling within the faster delta/theta range to the direction of attention, corresponding to task difficulty and accuracy. This result indicates a lateralized relationship between low-frequency rhythms and alpha-band activity, highlighting the role of alpha rhythms as a mediator of attention in audio-visual speech processing. Indeed, inhibitory alpha power fluctuation follows previous observations of sensory filtering. These findings underscore the importance of lateralized neural dynamics in tasks involving selective attention and suppression, providing new insights into the oscillatory mechanisms underlying audio-visual integration in human communication. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=56 SRC="FIGDIR/small/581860v3_ufig1.gif" ALT="Figure 1"> View larger version (14K): org.highwire.dtl.DTLVardef@1a7903org.highwire.dtl.DTLVardef@1fec365org.highwire.dtl.DTLVardef@ce4b12org.highwire.dtl.DTLVardef@1a2a4cd_HPS_FORMAT_FIGEXP M_FIG C_FIG This work describes how alpha power fluctuation varies as a function of attention during complex audiovisual stimuli. We identified that alpha power fluctuation in the delta-theta range increase as a function of task demands and corresponds to comprehension accuracy. By understanding how temporal-spatial alpha power dynamics influence attention, we describe a novel cross-frequency attention mechanism.