Sound by itself can be a reliable source of information about an object's size. For instance, we are able to estimate the size of objects merely on the basis of the sound they make when falling on the floor. Moreover, loudness and pitch are crossmodally linked to size. We investigated if sound has an effect on size estimation even in the presence of visual information, that is if the manipulation of the sound produced by a falling object influences visual length estimation. Participants watched videos of wooden dowels hitting a hard floor and estimated their lengths. Sound was manipulated by (A) increasing (decreasing) overall sound pressure level, (B) swapping sounds among the different dowel lengths, and (C) increasing (decreasing) pitch. Results showed that dowels were perceived to be longer with increased sound pressure level (SPL), but there was no effect of swapped sounds or pitch manipulation. However, in a sound-only-condition, main effects of length and pitch manipulation were found. We conclude that we are able to perceive subtle differences in the acoustic properties of impact sounds and use them to deduce object size when visual cues are eliminated. In contrast, when visual cues are available, only loudness is potent enough to exercise a crossmodal influence on length perception.
Keywords: impact sound; length estimation; loudness; multisensory perception; object size; pitch.