Unmasking the dichoptic mask by sound: spatial congruency matters

People tend to look toward where a sound occurs; however, the role of spatial congruency between sound and sight in the effect of sound facilitation on visual detection remains controversial. We propose that the role of spatial congruency depends on the reliability of the information provided by the facilitator; if it is relatively unreliable, adding spatially congruent information can help to unify different sensory inputs to compensate for this unreliability. To test this, we examine the influence of sound location on visual detection with a non-temporal task, presumably unfavorable for sound since it is better for temporal resolution, and predict that spatial congruency should matter in this situation. We used the continuous flash suppression paradigm that makes the visual stimuli invisible to keep the relationship of sound and sight opaque. The sound is on the same depth plane as the visual stimulus (the congruent condition) or on a different plane (the incongruent condition). The target was presented to one eye with luminance contrast gradually increased and continuously masked by flashed Mondrian masks presented to the other eye until the target was released from suppression. We found that sound facilitated visual detection (measured by released-from-suppression time) in the spatially congruent condition but not in the spatially incongruent condition. Together with previous findings in the literature, it is suggested that both task type and modality determine the reliability of the information for multisensory integration and thus determine whether spatial congruency is critical.