The effect of head movements on visual and auditory dominance.

Two experiments were performed to determine the effect of active auditory exploration (head movement) on visual and auditory dominance. In each experiment subjects located a small audio speaker unimodally or bimodally. On the bimodal trials a modality discordance was created by requiring prismatic viewing. Half the subjects in each experiment remained unaware of the discordance while the other half were informed that a prism was used, and its refracting properties were demonstrated. The second experiment differed from the first by allowing observers free head movement during target localization which was transduced and recorded electromechanically. The results indicated that knowledge of modality discordance greatly reduced visual bias of audition for observers with heads immobilized, but did not affect auditory bias of vision significantly. Observers permitted head movement but not provided with knowledge of discordance demonstrated visual bias which was substantially reduced from that found in the first experiment for no-knowledge subjects. Observers who were permitted head movement and provided with knowledge of discordance demonstrated no visual bias or auditory bias. Head movements were executed systematically, when permitted, and resulted in an increase in the precision of auditory localizations and a reduction in the biasing effect of vision. In contrast, head movement did not affect the precision of visual localizations. Results are discussed in terms of current hypotheses regarding perceptual dominance.