The effect of amplitude envelope on spatial ventriloquism

Spatial ventriloquism occurs when a visual event and an auditory event happen simultaneously; location judgments for the sound source become biased toward the location of the visual event. Evidence suggests the brain attributes greater weight to spatial information provided by the visual stimulus because the visual system offers better spatial acuity; when the visual stimulus is deteriorated, the visual bias is reduced. Thus, the brain performs optimal bimodal integration: greater weight is given to the modality which provides more information. The present study aims to determine whether the amplitude envelope of sounds provides spatial localization information to the perceptual system. We used a psychophysical staircase procedure to measure spatial ventriloquism experienced by participants for sounds with percussive, flat, and time-reversed percussive envelopes. We hypothesize that percussive and reverse-percussive sounds provide more information and thus better sound localization acuity than flat sounds, which would result in smaller degrees of spatial ventriloquism for the former than the latter. The results yield insight into the brain’s use of auditory cues in audio-visual integration.