Separation between Sound and Light Enhances Audio-Visual Prior Entry Effect

Yuki HONGOH  Shinichi KITA  Yoshiharu SOETA  

IEICE TRANSACTIONS on Information and Systems   Vol.E91-D   No.6   pp.1641-1648
Publication Date: 2008/06/01
Online ISSN: 1745-1361
DOI: 10.1093/ietisy/e91-d.6.1641
Print ISSN: 0916-8532
Type of Manuscript: Special Section PAPER (Special Section on Human Communication III)
Category: Human Information Processing
multisensory perception,  audio visual interaction,  temporal order judgment (TOJ),  prior entry effect,  

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We examined how spatial disparity between the auditory and visual stimuli modulated the audio-visual (A-V) prior entry effect. Spatial and temporal proximity of multisensory stimuli are crucial factors for multisensory perception in most cases (e.g. [1],[2]). However our previous research[3],[4] suggested that this well-accepted hypothesis was not applicable to the A-V prior entry effect. In order to examine the effect of the spatial disparity on the A-V prior entry effect, six loudspeakers and two light emitting diodes (LEDs) were used as stimuli. The loudspeakers were located at 10, 25, and 90 degrees from the midline of the participants to both right and left sides. A preceding sound was presented from one of these six loudspeakers. After the preceding sound, two visual targets were presented successively at a short interval and participants judged which visual target was presented first. Two colour changeable ('red' or 'green') LEDs were used for the visual targets and participants judged the order of visual targets by their colour not by their side in order to avoid the response bias as much as possible. The visual targets were situated at 10 degrees or 25 degrees from the participants' midline to both right and left in the Experiment 1. Results showed a biased judgment that the visual target at the sound presented side was presented first. The amplitude of the A-V prior entry effect was greater when the preceding sound source was more apart from the midline of participants. This effect of spatial separation indicated that the clarity of either right or left side of the preceding sound enhanced the amplitude of the A-V prior entry effect (Experiment 2). These results challenge the belief that the spatial proximity of multisensory stimuli is a crucial factor for multisensory perception.