Abstract: According to the statistically optimal integration theory, our brains weigh various sources of sensory information according to their reliabilities during multisensory integration. Recent behavioral studies have proposed that the prior knowledge about the reliability of different modalities can also play an important role in the weighting of different sensory information. The present study aimed to examine whether the prior knowledge affect multisensory integration in the early perceptual processing stage or in the post-perceptual processes stage.
Fourteen participants (19-24 years old) were tested when a single letter (“B” or “E”) was presented simultaneously in both auditory and visual modalities. The letter was displayed in one of the two colors. In one condition the visual information presented was always (probability of 100%) congruent with auditory information and this is the same for either color presented (equal-probability condition). In another condition, the probability in which the visual and auditory information was congruent was varied. The probability was 100% (high probability, HP) when the visual letter was in one color and the probability was 30% (low probability, HP) when the visual letter was in another color. Therefore different colors were associated with different probability (different-probability condition). The participants were instructed to press the button 1 for letter B and button 2 for letter E regardless of the color of the visual stimuli and regardless of the auditory information. Each participant completed 240 trials during equal-probability condition and 1500 trials (consisting of 5 experimental blocks) during different-probability condition.
Significantly different responses to the congruent audiovisual stimuli were found between HP and LP and the difference was only observed during block 4 and block 5 of difference-probability condition.
These results suggested the different probabilities of auditory-visual congruency modulate the response time to auditory-visual congruent stimuli, which suggested the prior knowledge regarding the reliability of sensory cues affects the multisensory integration in the early perceptual processing stage.

Key words: multisensory integration, prior knowledge, statistically optimal integration, reliability