# Stereo Vision Based Sensory Substitution for the Visually Impaired
## Implementation and Performance Evaluation
### Usability Assessment
Thus, the project devised efficient training resources, relying on valuable contribution from neuroscience, psychophysics and behavioral science specialists, best practices provided by Orientation and & Mobility instructors and on modern concepts like serious games. The above results of the usability assessment were obtained by the visually impaired users after three two-hour sessions of incremental training with the SoV system in virtual environments and indoor environments, followed by another four two-hour sessions which included training and testing in outdoor scenarios. When comparing SoV with the white cane, we found out that, for our sample of rather inexperienced white cane users, mobility with the SoV device was accomplished with performance comparable to the performance with the white cane, and sometimes better. The SoV system offers the clear advantage of informing the user about the presence of objects which could not be otherwise detected with the cane (head level objects or signs) or that could be missed by it (holes in the ground). Moreover, the system allows a good perception of walls which are very much used by VI people as a shoreline during navigation. With the SoV system, users could walk at a reasonable distance from the wall, without the need to hit it with the cane (average of 23 cane hits when using the white cane only, compared to 3.5 hits when using the white cane and SoV on a 30 m path) and could easily detect the corners of the buildings (with a 0.92 average accuracy over all tests). For inexperienced white cane users, mobility with the SoV device was accomplished with performance comparable to using the cane, and sometimes better. Users more experienced in using the white cane tend to rely more on the cane than on the system, when provided with both assistive devices. Less skilled white cane users chose to rely more on the SoV system. The added value of SoV compared to the white cane was reported by the participants to consist in: providing early feedback about static and dynamic objects (at a larger distance than the white cane), providing distinctive feedback about head-height objects, walls, negative obstacles and signs. A selection of videos showcasing some of the usability experiments can be accessed on the YouTube channel of the Sound of Vision project ([[https://www.youtube.com/channel/UC5](https://www.youtube.com/channel/UC5) MSSMmEG1 ABPZDoxzPIZoWQ]([https://www.youtube.com/channel/UC5](https://www.youtube.com/channel/UC5) MSSMmEG1 ABPZDoxzPIZoWQ)), one of the most illustrative for the outdoor evaluation being [[https://www.youtube.com/watch?v=3](https://www.youtube.com/watch?v=3) XIR2 RNy8 cg]([https://www.youtube.com/watch?v=3](https://www.youtube.com/watch?v=3) XIR2 RNy8 cg). Figure 8: Examples of outdoor testing scenarios: (**left**) Semi-controlled environment, in which the test consisted in walking along a building wall while avoiding hanging and ground-level obstacles; (**right**) uncontrolled environment, in which the test consisting in walking on a crowded sidewalk.