Chapter 14 Ventriloquism: A case of crossmodal perceptual grouping

The term ventriloquism refers to various manifestations of crossmodal spatial interaction between auditory and visual inputs which are observed in sensory conflict situations. These involve on-line manifestations like perceptual fusion in spite of spatial discrepancy and immediate crossmodal bias, by which localization of data in one modality are attracted toward conflicting data in the other modality, and also off-line aftereffects. Existing data concerning the variables on which the occurrence of the phenomena depend are reviewed, with insistence on the distinction between sensory and cognitive factors. A question which has been neglected in the literature consists of separating genuine perceptual contributions to the phenomena from voluntary post-perceptual adjustments. Using a new paradigm based on psychophysical staircases, we have shown that the visual bias of auditory location occurs even when the subject is not aware of the auditory-visual discrepancy, hence cannot reduce to voluntary corrections. Other experiments have demonstrated that ventriloquism cannot be explained by deliberate shifts of spatial attention. It is concluded that ventriloquism reflects a phenomenon of automatic crossmodal pairing, that is, formation of a cross-modal perceptual unit which takes place at a pre-conscious processing stage and thus must be clearly distinguished from conscious perceptual fusion. © 1999 Elsevier B.V. All rights reserved.SCOPUS: ar.k