Sonification is defined as presentation of information by means of non-speech audio. In assistive technologies for the blind, sonification is most often used in electronic travel aids (ETAs) - devices which aid in independent mobility through obstacle detection or help in orientation and navigation. The presented review contains an authored classification of various sonification schemes implemented in the most widely known ETAs. The review covers both those commercially available and those in various stages of research, according to the input used, level of signal processing algorithm used and sonification methods. Additionally, a sonification approach developed in the Naviton project is presented. The prototype utilizes stereovision scene reconstruction, obstacle and surface segmentation and spatial HRTF filtered audio with discrete musical sounds and was successfully tested in a pilot study with blind volunteers in a controlled environment, allowing to localize and navigate around obstacles.
In this paper we propose an electronic travel aid system for the visually impaired that utilizes interactive sonification of U-depth maps of the environment. The system is comprised of a depth sensor connected to a mobile device and a dedicated application for segmenting depth images and converting them into sounds in real time. An important feature of the system is that the user can interactively select the 3D scene region for sonification by simple touch gestures on the mobile device screen. The sonification scheme is using stereo panning for azimuth angle localization of scene objects, loudness for their size and frequency for distance encoding. Such a sonic representation of 3D scenes allows the user to identify the geometric structure of the environment and determine the distances to potential obstacles. The prototype application was tested by three visually impaired users who managed to successfully perform indoor mobility tasks. The system's usefulness was evaluated quantitatively by means of system usability and task-related questionnaires.
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