Influence of visual stimulus on the precedence effect in sound localization

In this paper we examine how the precedence effect is affected by concurrent visual information about the source of sound. In the experiment, speech, snare drum and guitar sounds were used as sound stimuli, and moving images of the speech utterances or musical performances recorded synchronously with the sounds were presented as visual stimuli. Thus, differences in the lower limit (summing localization threshold, SLT) and the upper limit (echo threshold, ET) of the area where the precedence effect operates were observed when visual stimuli were presented and not presented. As a result, the following conclusions were drawn: 1) The influence of a visual stimulus on SLT was significant for speech and the drum sound, and there was a tendency that SLT was shortened, but for the guitar sound the influence was less significant. 2) The presentation of a visual stimulus along with an auditory stimulus significantly prolonged ET for the guitar sound, but no definite tendency was observed for speech and the drum sound. 3) SLT appears to be significantly influenced by the characteristics of the audiovisual stimulus, particularly by the dynamics of its movement. ET also changed significantly in the presence of a visual stimulus but the change was not uniform; it appeared to depend on the object of attention, i.e., the auditory stimulus, visual stimulus or both.