Perceived size change induced by audiovisual temporal delays.

The retinal image of an object does not contain information about its actual size. Size must instead be inferred from extraretinal cues for which distance information makes an essential contribution. Asynchronies in the arrival time across visual and auditory sensory components of an audiovisual event can reliably cue its distance, although this cue has been largely neglected in vision research. Here we demonstrate that audio-visual asynchronies can produce a shift in the apparent size of an object and attribute this shift to a change in perceived distance. In the present study participants were asked to match the perceived size of a test circle paired with an asynchronous sound to a variable-size probe circle paired with a simultaneous sound. The perceived size of the circle increased when the sound followed its onset with delays up to around 100 ms. For longer sound delays and sound leads, no effect was seen. We attribute this selective modulation in perceived visual size to audiovisual timing influences on the intrinsic relationship between size and distance. This previously unsuspected cue to distance reveals a surprisingly interactive system using multisensory information for size/distance perception.