How ambiguous is an audio-visual impact?

When two similarly sized white disks are seen to move toward each other, coincide and then move apart, the usual perception is to see the figures as passing despite the perception of an impact being equally plausible. However, if a brief sound is presented at the moment of coincidence this perception is reversed and the objects are seen to collide. Most interpretations of this observation emphasise the role of sound in disambiguating the visual stimulus however the sound induced bounce effect occurs even when the objects unambiguously pass by each other (as for example when one is a disk and the other a square). We will report a series of experiments in which we varied a number of characteristics of the visual stimuli without removing the effect of the sound. It appears that the saliency of a sound is paramount in the perception of an audio-visual impact event