How do irrelevant stimuli from another modality influence responses to the targets in a same-different task

It remains unclear whether multisensory interaction can implicitly occur at the abstract level. To address this issue, a same-different task was used to select comparable images and sounds in Experiment 1. Then, the stimuli with various levels of discrimination difficulty were adopted in a modified same-different task in Experiments 2, 3, and 4. The results showed that only when the irrelevant stimuli were easily distinguishable, a consistency effect could be observed in the testing phase. Moreover, when easily distinguishable irrelevant stimuli were simultaneously presented with difficult target stimuli, irrelevant auditory stimuli facilitated responses to visual targets whereas irrelevant visual stimuli interfered with responses to auditory targets in the training phase, indicating an asymmetry in the role of visual and auditory in abstract multisensory integration. The results suggested that abstract multisensory information could be implicitly integrated and the inverse effectiveness principle might not apply to high-level processing of abstract multisensory integration.