Mini-Review of Technologies for Mobility of the Visually Impaired

As mobility is significantly correlated with autonomy and quality of life, a clear majority of the developed approaches and devices dedicated to visually impaired individuals attempts to augment or support orientation and mobility abilities and maximize independence and safety. Therefore, various methods and technical solutions have been proposed for generating a representation of the visual scene and transmitting this information to the user. As different visual impairments can be distinguished, from congenital blindness to low vision, dedicated solutions have been put forward to accommodate these different needs and abilities. These solutions may be used universally or take advantage of the specificity of the visual impairment (e.g. low vision, late blindness). Through the presentation of sensory supplementation, technical aids and visual neuro-prostheses studies, we will explore some of the approaches and technical solutions that have been proposed or are still in development. Additionally, we will discuss the benefits of providing specialized information dedicated to mobility as opposed to a general-purpose representation. Abbreviations: VIVisually Impaired; TVSSTactile Vision Substitution System; TDUTongue Display Unit; RPRetinitis Pigmentosa; AMDAge Related Macular Degeneration; DBRDepth-Based Representation; LBRLuminosity-Based Representation Biomedical Journal of Scientific & Technical Research Volume 9Issue 1: 2018 Cite this article: Guillaume T, Edwige P. Mini-Review of Technologies for Mobility of the Visually Impaired. Biomed J Sci&Tech Res 9(1)2018. BJSTR. MS.ID. 001732. DOI: 10.26717/ BJSTR.2018. 09.001732. 6825 of adapted cues, clues and landmark information for static and dynamic scene objects location. In the subsequent sections are addressed scene representation used in sensory supplementation devices (Section II), in augmented and virtual reality (Section III), in visual neuro-prostheses (Section IV) Technical Aid and Sensory Supplementations Systems This section presents an overview of non-invasive sensory supplementation systems, which provide geometric information to the user about its surroundings as well as information pertinent to mobility. In these systems, information usually acquired from one sensory modality is captured through an artificial sensor (e.g. video camera) and is processed to create stimuli adapted to another modality. Two main categories of these devices can be distinguished to supplement the sense of vision: visuo-tactile and visuo-auditory systems. Visuo-Tactile Sensory Supplementation Various systems have been proposed so far; some of the most representative are presented hereafter. Scene Representation Through the Tactile Sense Figure 1: Young visually impaired subject reproducing hand gesture perceived through a head-worn camera and a 6x24 vibrotactile array. The LED monitor in the foreground shows the active pattern of the tactile display [1]. The Bach-y-Rita’s TVSS (tactile vision substitution system [1]) is one of the early developed and most well-known visual to tactile sensory supplementation devices. The system converts an image captured by a video camera to generate tactile stimuli through a stimulation device placed on a part of the body (skin) such as the lower back, the abdomen or the fingertip in the first version of the system. Captured color images are transformed into black and white images and reduced spatially to accommodate for tactile device resolution (between 100 and 1032 stimulation points). Figure 1 shows a blind child reproducing hand gesture with the TVSS (placed on the table in front of the child). In [2], extending the initial work of Bach-y-Rita, Collins et al. have developed a 1024 wearable electrotactile system placed on the abdomen and converting images acquired through a 90° field of view camera. As a result, subjects equipped with such device have been able to safely avoid and navigate around large and contrasted objects. However, these results are only valid in simple indoor environment as subjects, even trained, failed to use the system in real outdoor environment. This setup was later modified into a tongue display unit (TDU), also called Brain Port, which requires reduced electrical current for the stimulation and was more suitable for mobility purpose [3]. Some research teams have developed a “specialized” representation approach to present relevant and adapted information for mobility. Space Representation in Mobility Support In [4], the authors propose a novel scene representation method dedicated to mobility. In their approach, the 3D scene captured by a stereoscopic pair of cameras, is projected vertically (i.e. gravitationally/orthographic projected) on a 2D plan. Through the proposed processing, obstacles are represented as nonaccessible areas on the plan, whether they are overhanging or lying on the ground. The obtained simplified map of the environment is then presented to the user through a hand-held touch stimulating Braille-like device (Figure 2) and is updated in real-time. In the proposed representation, processing of the 3D data allows a binary partitioning of the space into two zones: obstacle-free and obstacles. The system is aimed to provide a dynamical tactile representation of the scene where raised taxels (i.e. individual tactile stimulators that compose the device) principally show the limits of the obstacles-free space. Furthermore, information is represented on the tactile surface in a user-centered Euclidian reference frame which observation point is indicated by a notch on one of the borders of the tactile surface. Preliminary navigation experiments in standardized test environments indicate that the system can be used to perceive the spatial layout of the dynamical environment (named tactile gist [5]) through this binary tactile representation. Figure 2: Illustration of the developed scene representation (bottom row) and device (top row). Images of the scene, acquired with a stereo rig, are processed to create a 2D tactile map (right image). This simplified representation (tactile gist) shows dynamically the accessible and nonaccessible parts of the environment delimited by raised taxels. The origin of the Euclidian reference frame is attached to the tactile map and is materialized by a notch in one of the device borders. The stimulation device is a Braille matrix of 8 by 8 shape memory alloys based taxels [4,5,6]. Biomedical Journal of Scientific & Technical Research Volume 9Issue 1: 2018 Cite this article: Guillaume T, Edwige P. Mini-Review of Technologies for Mobility of the Visually Impaired. Biomed J Sci&Tech Res 9(1)2018. BJSTR. MS.ID. 001732. DOI: 10.26717/ BJSTR.2018. 09.001732. 6826 In [6], the authors propose a representation of the 3D scene like [4], except that there is no notch on the necklace-like device (overhanged over the neck) what increase the cognitive load for localization in the representation; for these reasons, this device have been replaced by a tactile belt which does not use an external explicite representation of the space. As another approach to mobility, Chekhchoukh et al. [3] propose a guidance technique using also the TDU based on a symbolic scene presentation. The authors mainly propose to generate a 3D path composed of dots that must be followed to travel from one place to another. Stimulus intensity associated to each dot represent the distance of this 3D dots from the user. Visuo-Auditory Sensory Supplementation Visual to auditory sensory supplementation systems may be categorized into two approaches: a) The auditory coding of the position and distance of the obstacles through the use of an ultrasonic, infrared or laser rangefinder device for instance; b) A visual to sound real time translation based on the coding of visual patterns extracted from captured images (e.g. from a head mounted camera). Range Finder Devices In this class, the auditory feedback provided by such devices gives the user information about the texture, the distance, the size and position of the scene entities. In these devices, distance is mainly represented by the sound intensity and the positions of objects around the user are coded through binaural disparity. For instance, the C-5 laser cane [7] is a triangulation-based device, embedded in a white cane. Obstacle detection output information on obstacles in three different zones (at head height, in front of the user and on the ground) by generating a specific tone. Vision to Sound Scene Translation In this class, image is converted appropriately into sound. One of the most well-known devices of this class is the voice developed by Meijer et al. [8]. It proposes an image to sound conversion of the captured video frame pixel arrays into successive sound signals. Each signal is generated according to the pixel position and brightness: pitch is proportional to pixel height (vertical position), amplitude (loudness) to brightness. To give information on the horizontal position of the stimulus, a left to right scanning technique has been implemented (“synchronization” sound click indicates the start of a frame scan). There are very few visually impaired people using the voice as the proposed representation is very complex and learning phase requires several years. Using Residual Vision: Augmented and Virtual Reality Devices Several visual disorders such as retinitis pigmentosa (RP), age related macular degeneration (AMD) or glaucoma may induce severe vision loss. Indeed, persons suffering from low vision may experience significant visual field reduction (like in RP patients) or central vision loss in the case of AMD for instance, visual defects (e.g. scotoma) and other visual impairments (e.g. reduced contrast sensitivity, impaired color vision). Augmented and virtual reality devices make possible, to a certain extent, to compensate these visual impairments by: a) Providing additional information in the remaining field of view. Without such technical ai