The rhythm of sensory input shapes audio-visual temporal processing

The temporal relationship between incoming signals is crucial in determining whether multisensory information is integrated into unitary percepts. Temporal binding windows (TBWs) define the time range within which multisensory inputs are highly likely to be perceptually integrated, even if asynchronous. TBWs widen with stimulus complexity and neurodevelopmental conditions (e.g., autism and schizophrenia), yet the key factors underlying their malleability remain unclear. The (quasi)rhythmic properties of sensory inputs, frequently embedded in natural stimuli (e.g., speech), are among the possible exogenous modulators. Indeed, stimulus spectral features can influence the alignment of neural excitability across sensory regions, synchronizing brain rhythms with external rhythmic patterns through phase-reset mechanisms and neural entrainment. In a series of psychophysical studies, we presented simultaneity judgement tasks with pulsing audio-visual (AV) streams amplitude-modulated according to different regular frequencies or following purely rhythmic vs. quasi-rhythmic (speech-like) envelopes. Results show that TBWs decrease as the stimulus frequency increases and that speech-like streams are integrated across larger TBWs. These findings highlight the importance of stimulus spectral structure in shaping multisensory perception. Furthermore, they show that quasi-rhythmic spectrotemporal features of speech-like streams induce more tolerant cross-modal temporal processing even when the leading stimulation frequency is controlled for, putatively reflecting an adaptation to the variable rhythmic structure of natural speech. Our results align with neurophysiological accounts of neural entrainment and motivate future research in clinical populations with multisensory processing deficits.