The brain apparently remaps the perceived locations of simultaneous auditory and visual events into a unified audio-visual space to integrate and/or compare multisensory inputs. However, there is little qualitative or quantitative data on how simultaneous auditory and visual events are located in the peripheral visual field (i.e., outside a few degrees of the fovea). We presented a sound burst and a flashing light simultaneously not only in the central visual field but also in the peripheral visual field and measured the relative perceived locations of the sound and flash. The results revealed that the sound and flash were perceptually located at the same location when the sound was presented at a 5°p eriphery of the flash, even when the participants' eyes were fixed. Measurements of the unisensory locations of each sound and flash in a pointing task demonstrated that the perceived location of the sound shifted toward the front, while the perceived location of the flash shifted toward the periphery. As a result, the discrepancy between the perceptual location of the sound and the flash was around 4°. This suggests that the brain maps the unisensory locations of auditory and visual events into a unified audio-visual space, enabling it to generate unisensory spatial information about the events.
In our previous studies, a perceptual phenomenon, audio-visual peripheral spatial disparity (AVPSD), has been found. The spatial coincidence of perceived locations of a sound and flash presented in the peripheral field varies from their coincident physical location. Since the stimulus condition used in the previous experiments was limited, three new experiments were conducted to investigate the robustness of the spatial disparity between the perceptual and physical locations of the sound and flash. In Experiments 1 and 2, the frequency characteristics of the sound and the repetition of stimulus appearance were respectively changed from those used in the previous experiments. In Experiment 3, the presentation timing of the sound or the flash was delayed for one second. The results of Experiments 1 and 2 show that the spatial disparity was robustly appeared. In contrast, the spatial disparity disappeared in Experiment 3. These results suggest that the features of the stimulus pattern do not affect the spatial disparity, but the simultaneity of the sound and flash plays an essential role. Acknowledgment: This research was supported by a Grant-in-Aid for Specially Promoted Research (No. 19001004) and Grant-in-Aid for Young Scientists (B) (No. 21730584).
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