Abstract
A combined presentation of a weak visual target and an auditory tone leads to quicker, more accurate responses, and a higher subjective report of signal intensity (e.g., visual awareness). This phenomenon has been suggested to be due to either multisensory integration or a rise in attention (arousal), with more alertness induced by the combined stimuli. To explore these alternative explanations, we conducted three experiments in which Continuous Flash Suppression (CFS) was used to manipulate awareness of visual targets that were presented on their own or together with a brief tone. Processing speed and awareness were measured in experiments 1 and 2 on a trial by trial basis. The findings indicate that the presence of a tone was associated with faster responses and more instances of awareness of the visual target, even when the tone was not task-relevant. In a third experiment we specifically addressed the relationship between detection of location of a visual target with presence/absence of an auditory informative (spatially congruent), uninformative or misdirecting (spatially incongruent) sound.
Analysis of detection scores point towards a multisensory integration explanation as spatial congruency between the auditory and visual targets was associated with a combination of improved detection and increased awareness. When the tone was incongruent or uninformative both detection and instances of aware responses were higher than when the visual target was presented alone, which is consistent with the explanation based on the effect of attention.
In conclusion, the effect of speeded processing, increased detection and higher instances of subjective report of awareness of the visual targets could be explained by both multisensory integration and a rise in attention/alertness.