Interactions between front-back confusion and visual capture in summing localization

Abstract

Ambiguity in binaural timing and level information often causes front-back confusions in sound localization. This experiment investigated the extent to which front-back confusions are modulated by concurrent visual stimuli. 15-ms duration noise stimuli were presented over two loudspeakers positioned at ±45o in front or behind a listener with a delay between them of −1—1 ms in steps of 0.5 ms, thus evoking summing localization. These sound stimuli were presented with or without light-flash stimuli at three different frontal locations. In comparison to audio only trials, when visual stimuli were also presented front-back confusion decreased for sound stimuli presented in front and increased for rear-presented auditory stimuli. This effect was greater for phantom sound sources than single speaker controls. These results suggest that visual cues influence the perceived location of a sound source when it is outside the field of vision. Further, the phantom sound sources presented using “summing localization” may offer less robust localization cues than physical sound sources, resulting in greater front-back confusion and stronger visual capture. Acoustic analyses of binaural and spectral cues are conducted to identify potential causes of the differences in FBC rates between single speaker and phantom sound sources.