Examining How Interaural Differences Owing to Head Rotation during Walking Improve the Distance of Auditory Obstacle Perceptions among Individuals with Visual Impairment: A Case Study in Small-Scale Blind Group.

The ability of individuals with visual impairment to recognize an obstacle by hearing is called "obstacle sense". This ability is facilitated while they are moving, though the exact reason remains unknown. This study aims to clarify which acoustical factors may contribute to obstacle sense, especially obstacle distance perception. First, we conducted a comparative experiment regarding obstacle distance localization by individuals who are blind (N = 5, five men with blindness aged 22-42 (average: 29.8)) while they were standing and walking. The results indicate that the localized distance was more accurate while walking than while standing. Subsequently, the head rotation angle while walking and acoustic characteristics with respect to obstacle distance and head rotation angle were investigated. The peaks of the absolute head rotation angle during walking ranged from 2.78° to 11.11° (average: 6.55°, S.D.: 2.05°). Regarding acoustic characteristics, acoustic coloration occurred, and spectral interaural differences and interaural intensity differences were observed in the blind participants (N = 4, four men including two blind and two control sighted persons aged 25-38 (average: 30.8)). To determine which acoustic factors contribute, we examined the threshold of changes for interaural differences in time (ITD) and intensity (IID) (N = 11, seven men and four women with blindness aged 21-35 (average: 27.4)), as well as coloration (ICD) (N = 6, seven men and a woman with blindness aged 21-38 (average: 29.9))-depending on the head rotation. Notably, ITD and IID thresholds were 86.2 µs and 1.28 dB; the corresponding head rotation angles were 23.5° and 9.17°, respectively. The angle of the ICD threshold was 6.30° on average. Consequently, IID might be a contributing factor and ICD can be utilized as the cue facilitating the obstacle distance perception while walking.

Binaural Listening with Head Rotation Helps Persons with Blindness Perceive Narrow Obstacles.

Orientation and mobility (O&M) are important abilities that people with visual impairments use in their independent performance of daily activities. In orientation, people with total blindness pinpoint nonsounding objects and sounding objects. The ability to perceive nonsounding objects is called obstacle sense, wherein people with blindness recognize the various characteristics of an obstacle using acoustic cues. Although body movement and listening style may enhance the sensing of obstacles, experimental studies on this topic are lacking. Elucidating their contributions to obstacle sense may lead to the further systematization of techniques of O&M training. This study sheds light on the contribution of head rotation and binaural hearing to obstacle sense among people with blindness. We conducted an experiment on the perceived presence and distance of nonsounding obstacles, which varied width and distance, for participants with blindness under the conditions of binaural or monaural hearing, with or without head rotation. The results indicated that head rotation and binaural listening can enhance the localization of nonsounding obstacles. Further, when people with blindness are unable to perform head rotation or use binaural hearing, their judgment can become biased in favor of the presence of an obstacle due to risk avoidance.