Abstract
Multisensory stimuli are processed with higher speed and accuracy than could be expected based on responses to the unisensory components. This redundant signal effect (RSE) holds true both for healthy populations and individuals for whom stimulus detection and awareness are dissociated due to neurological complications. Pairing visual targets with concurrent stimulation in a different modality may improve subjective visual awareness, but the mechanisms for such interactions are unclear. In a behavioural experiment we investigated the role of subjective visual awareness in multisensory RSE. Continuous Flash Suppression (CFS) was used to reduce the awareness of visual targets. Participants were asked to press a response button if they saw or heard audio-visual stimuli. A visual target or an auditory tone were either presented alone or simultaneously. Speed and accuracy for stimulus detection were measured alongside subjective visual awareness. A benefit was seen in multisensory trials across all behavioural measures but only when participants were consciously aware of the visual target. The incidence rate of subjective awareness of the visual target was not affected by the simultaneous presentation of an auditory target. To further investigate the reaction time data, a Shifted Wald (SW) model was applied to the pooled RT distributions. Computational modelling revealed lower gain and threshold parameters in the reaction time distributions of unaware multisensory trials compared to the aware multisensory trials. These findings indicate that for a given audio-visual stimulus, the state of conscious visual awareness can lead to differences in reaction times and computational modelling is a useful tool to explore the differences in characteristics of the underlying cognitive functions in multisensory stimuli.