Linking Auditory-Induced Bouncing and Auditory-Induced Illusory Crescents: an Individual-Differences Approach

When two disks move toward each other, overlap, and then move apart, the visual system can resolve the ambiguity either as two disks streaming past each other or two disks bouncing off each other. Presenting a brief beep at the moment of overlap has been observed to increase the proportion of reported bouncing impressions (i.e., auditory-induced bouncing) as well as to reduce the perceived overlap between the disks (leaving a larger uncovered crescent; auditory-induced illusory crescents). Previous research has speculated about the relationship between both variables, but no direct evidence has been reported yet. We present an individual-differences study in which our participants completed the bouncing/streaming task as well as the illusory crescent task on two consecutive days (to obtain test–retest reliabilities). We obtained acceptable to good reliabilities for the effect of the tone in both dependent measures. Most importantly, auditory-induced bouncing and auditory-induced illusory crescents were correlated in the moderate range suggesting that both illusions are related and share common underlying cognitions. Yet, moderate correlations also indicate that both measures partially capture distinct aspects of the object correspondence.