High attentional load enhances the susceptibility to non-speech audiovisual illusions

The role of attentional processes in the integration of input from different sensory modalities is complex and multifaceted. Importantly, little is known about how simple, non-linguistic stimuli are integrated when the resources available for sensory processing are exhausted. We studied this question by examining multisensory integration under conditions of limited endogenous attentional resources. Multisensory integration was assessed through the sound-induced flash illusion (SIFI), in which a flash presented simultaneously with two short auditory beeps is often perceived as two flashes, while attentional load was manipulated using an n-back task. A one-way repeated measures ANOVA revealed that attentional load had a significant effect on the perception of the illusion while post-hoc tests showed that participants’ illusion perception was increased in high compared to low attentional load conditions. Additional analysis demonstrated that this effect was not related to a response bias. These finding provides evidence that the integration of non-speech, audiovisual stimuli is enhanced under high attentional load and it therefore supports the notion that top-down attentional control plays an essential role in multisensory integration.