# Effects of Visually Induced Self-Motion on Sound Localization Accuracy
## 4 Discussion  
We examined the effects of visually induced self-motion on the ability of listeners to determine their subjective midline orientation accurately. If self-motion information is crucial for auditory space perception [7, 25], the deterioration of sound localization accuracy can be observed in the case of self-motion perception, even if the motion is not physically induced. Our results showed that, in terms of detection thresholds of the subjective midline, the sound localization accuracy was lower under the vector condition than under the control condition. Thus, the results indicate that sound localization accuracy deteriorates under visually induced self-motion perception. These findings support the idea that self-motion information is crucial for auditory space perception [7, 25]. As mentioned before, under the visually induced self-motion, no change was observed in the auditory input difference between the two ears because the listener did not perform  
Figure 3: Average JNDs and standard errors. Figure 2: Average subjective midline and standard errors. any head/body movement. Therefore, our results did not support the assumption that the deterioration of sound localization accuracy is attributable to bottom-up effects, such as ear-input blurring. Previous studies have provided evidence of shared neurophysiological substrates for visual and vestibular processing on self-motion perception [29, 30, 31]. Accordingly, a more appropriate explanation could be that the deterioration of sound localization accuracy depends on self-motion information, irrespective of the origin of this information. Curiously, we also observed a slight leftward bias in the subjective midline. Specifically, there seemed to be a bias toward the left by approximately two degrees. It is difficult to ascertain the reason underlying the leftward bias. Notably, however, [PERSON] et al. [32] obtained similar results. In their study [32], participants were asked to judge whether visual stimuli were located toward the left or right of their body's midline. Artificial vestibular stimulation was applied to stimulate vestibular organs. They found that artificial stimulation of the vestibular system biased the perception of the body's midline. Furthermore, they also reported a slight but not significant leftward bias in body-midline localization without vestibular stimulation [32]. We found that the counterclockwise and clockwise conditions did not bias the auditory detection in opposite directions. Our results did not correspond with those of [PERSON] et al. [32] and are not consistent with the findings of previous studies that investigated the effects of visually induced self-motion on sound localization accuracy [7, 25]. In the section condition of the present study, the participants were instructed to press the switch button if they perceived self-motion. Immediately after the participants pressed the button, the acoustic stimulus was deployed from one loudspeaker and the participants were asked to determine the direction of the sound image. Therefore, it is possible that the self-motion information presented to the listeners was shorter and more limited than that in previous studies [7, 25] because the participants had not experienced the section for a certain period. Our results showed that in terms of detection thresholds based on the subjective midline, the sound localization accuracy was lower under the section condition than under the control condition. The statistical differences between the section and non-section conditions were significant, even though they may seem small. [PERSON] [33] reported that azimuthal sound localization in humans is most accurate in the straight-ahead orientation. The small difference may be due to the fact that we measured the sound localization accuracy of the listener's midline. However, we believe that this difference is worth noting. It is well known that self-motion facilitates sound localization performance.