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The Content of Imagined Sounds Changes Visual Motion Perception in the Cross-Bounce Illusion

DOI: 10.1038/srep40123
Berger, C. C., & Ehrsson, H. H. (2017). The content of imagined sounds changes visual motion perception in the cross-bounce illusion. Scientific Reports, 7(1). doi:DOI: 10.1038/srep40123

Abstract

Can what we imagine hearing change what we see? Whether imagined sensory stimuli are integrated with external sensory stimuli to shape our perception of the world has only recently begun to come under scrutiny. Here, we made use of the cross-bounce illusion in which an auditory stimulus presented at the moment two passing objects meet promotes the perception that the objects bounce off rather than cross by one another to examine whether the content of imagined sound changes visual motion perception in a manner that is consistent with multisensory integration. The results from this study revealed that auditory imagery of a sound with acoustic properties typical of a collision (i.e., damped sound) promoted the bounce-percept, but auditory imagery of the same sound played backwards (i.e., ramped sound) did not. Moreover, the vividness of the participants’ auditory imagery predicted the strength of this imagery-induced illusion. In a separate experiment, we ruled out the possibility that changes in attention (i.e., sensitivity index d′) or response bias (response bias index c) were sufficient to explain this effect. Together, these findings suggest that this imagery-induced multisensory illusion reflects the successful integration of real and imagined cross-modal sensory stimuli, and more generally, that what we imagine hearing can change what we see.

Authors

  • Christopher C. Berger1
  • H. Henrik Ehrsson1

What This Study Is About

The researchers wanted to know if imagining a sound could trigger a visual illusion. They used the "cross-bounce illusion," where two dots moving toward each other can look like they either pass through each other or bounce off like billiard balls.

How They Studied It

The team tested 72 participants. While watching two dots move on a screen, participants were asked to:
  • Imagine a "clink" sound (a "damped" sound that suggests a collision).
  • Imagine a "whoosh" sound (the same sound played backward, which doesn't sound like a hit).
  • Listen to real sounds to see if imagination worked as well as reality.

What They Found

When people imagined a "clink" at the exact moment the dots met, they were significantly more likely to see the dots bounce instead of cross.
  • Imagining the backward "whoosh" sound didn't cause the bounce.
  • The more vivid (realistic and clear) a person’s mental hearing was, the stronger the illusion became.
  • The effect was almost as strong as hearing a real sound!

What This Might Mean

This suggests that our brains don't keep imagination and reality in separate boxes. Instead, the brain is like a director, mixing "special effects" from our imagination into the live footage of what we see.
For the aphantasia community, this is a big clue. If you can’t imagine the sound, your brain might not "force" the dots to bounce. While this study didn't test aphantasics specifically, it suggests that people with aphantasia might actually see a more "accurate" version of the world, free from the interference of mental imagery.

One Interesting Detail

The brain is a smart detective: the illusion only worked if the imagined sound was "ecologically relevant"—meaning it had to sound like a real-world collision. If the sound didn't make sense for a bounce, the brain simply ignored it!
This summary was generated by AI and may contain errors. Always refer to the original paper for accuracy.