There are significant intra-individual and inter-individual variabilities in audiovisual temporal perception. Previous studies have shown that prestimulus neural variability could reflect behavioral variabilities. We aimed to investigate whether prestimulus neural variability can predict behavioral variability in audiovisual temporal perception. Furthermore, We also explored whether prestimulus neural variability directly influences behavioral responses or indirectly impacts perceptual decisions through post-stimulus-evoked responses. We analyzed the electroencephalography (EEG) data from a paradigm where the twenty-eight human subjects performed a simultaneity judgment (SJ) task in the beep-flash stimulus. The prestimulus weighted permutation entropy (WPE) was the indicator of neural variability in this study. We found that prestimulus frontal WPE could predict the individual's TBW in auditory- and visual-leading conditions. In addition, increased prestimulus parietal WPE was associated with more asynchronous responses. Prestimulus frontal WPE may be associated with top-down cognitive control, while parietal WPE may be related to bottom-up cortical excitability. Furthermore, poststimulus evoked responses could mediate the relation between prestimulus WPE and the individual's TBW or perceptual responses. These results suggested that prestimulus WPE was a marker in reflecting intra-individual and inter-individual variabilities in audiovisual temporal perception. Significantly, prestimulus WPE might influence perceptual responses by affecting poststimulus sensory representations.

ObjectivePerceptual integration and segregation are modulated by the phase of ongoing neural oscillation whose frequency period is broader than the size of the temporal binding window (TBW). Studies have shown that the abstract beep-flash stimuli with about 100 ms TBW were modulated by the alpha band phase. Therefore, we hypothesize that the temporal perception of speech with about hundreds of milliseconds of TBW might be affected by the delta-theta phase.MethodsThus, we conducted a speech-stimuli-based audiovisual simultaneity judgment (SJ) experiment. Twenty human participants (12 females) attended this study, recording 62 channels of EEG.ResultsBehavioral results showed that the visual leading TBWs are broader than the auditory leading ones [273.37 ± 24.24 ms vs. 198.05 ± 19.28 ms, (mean ± sem)]. We used Phase Opposition Sum (POS) to quantify the differences in mean phase angles and phase concentrations between synchronous and asynchronous responses. The POS results indicated that the delta-theta phase was significantly different between synchronous and asynchronous responses in the A50V condition (50% synchronous responses in auditory leading SOA). However, in the V50A condition (50% synchronous responses in visual leading SOA), we only found the delta band effect. In the two conditions, we did not find a consistency of phases over subjects for both perceptual responses by the post hoc Rayleigh test (all ps > 0.05). The Rayleigh test results suggested that the phase might not reflect the neuronal excitability which assumed that the phases within a perceptual response across subjects concentrated on the same angle but were not uniformly distributed. But V-test showed the phase difference between synchronous and asynchronous responses across subjects had a significant phase opposition (all ps < 0.05) which is compatible with the POS result.ConclusionThese results indicate that the speech temporal perception depends on the alignment of stimulus onset with an optimal phase of the neural oscillation whose frequency period might be broader than the size of TBW. The role of the oscillatory phase might be encoding the temporal information which varies across subjects rather than neuronal excitability. Given the enriched temporal structures of spoken language stimuli, the conclusion that phase encodes temporal information is plausible and valuable for future research.