Audiovisual misperceptions and oscillatory timescales: synergistic markers across the psychosis continuum?

Combining information across senses is a core property of human cognition, reliant on temporal binding windows (TBW) that arbitrate the perceptual fate of multisensory events. Wider audiovisual TBW have been associated with misperceptions such as the Sound-Induced Flash Illusion (SIFI), with greater susceptibility reported along the psychosis continuum. Individual alpha frequency (IAF), an electroencephalographic (EEG) marker proposed to pace visual sampling resolution, stands among the most compelling neural candidates for scaffolding these computations. As such, the present thesis offers an overarching view of multisensory perception, the SIFI, and alpha rhythms. This furnished a departure point to test whether reduced visuo-temporal acuity constitutes the mechanistic fingerprint of enlarged audiovisual TBW among psychosis-prone individuals, and whether occipital IAF serves as its primary causal determinant. In a first experiment using a revised SIFI paradigm, high-schizotypy individuals displayed broader TBW and reduced visuo-temporal precision relative to controls, with effects scaling with positive-like sub-traits. A scoping review then highlighted how resting-state IAF slowing corresponds to a consistent, trait-like feature in psychotic disorders. This was followed by a feasibility study validating rhythmic transcranial magnetic stimulation (rhTMS) as a testing protocol to probe the oscillatory contributions to the SIFI. In a final rhTMS–EEG co-registered experiment, prestimulus IAF was causally manipulated in participants performing a SIFI task. Contrary to our predictions, faster IAF primarily produced trait-dependent shifts toward a more liberal response criterion, increasing extra-flash illusory reports in individuals with elevated positive traits. Taken together, these findings argue that positive schizotypal traits chiefly index reduced temporal precision, thereby positioning the SIFI as a promising addendum to pre-emptive screening routines. By contrast, the present causal evidence does not provide conclusive support for IAF as a control parameter of audiovisual sensitivity, suggesting that, under specific experimental regimes, IAF manipulation is more readily expressed as trait-gated shifts in decisional policies.