Sensory substitution devices (SSDs) have come a long way since first developed for visual rehabilitation. They have produced exciting experimental results, and have furthered our understanding of the human brain. Unfortunately, they are still not used for practical visual rehabilitation, and are currently considered as reserved primarily for experiments in controlled settings. Over the past decade, our understanding of the neural mechanisms behind visual restoration has changed as a result of converging evidence, much of which was gathered with SSDs. This evidence suggests that the brain is more than a pure sensory-machine but rather is a highly flexible task-machine, i.e., brain regions can maintain or regain their function in vision even with input from other senses. This complements a recent set of more promising behavioral achievements using SSDs and new promising technologies and tools. All these changes strongly suggest that the time has come to revive the focus on practical visual rehabilitation with SSDs and we chart several key steps in this direction such as training protocols and self-train tools.

Distinct preference for visual number symbols was recently discovered in the human right inferior temporal gyrus (rITG). It remains unclear how this preference emerges, what is the contribution of shape biases to its formation and whether visual processing underlies it. Here we use congenital blindness as a model for brain development without visual experience. During fMRI, we present blind subjects with shapes encoded using a novel visual-to-music sensory-substitution device (The EyeMusic). Greater activation is observed in the rITG when subjects process symbols as numbers compared with control tasks on the same symbols. Using resting-state fMRI in the blind and sighted, we further show that the areas with preference for numerals and letters exhibit distinct patterns of functional connectivity with quantity and language-processing areas, respectively. Our findings suggest that specificity in the ventral ‘visual’ stream can emerge independently of sensory modality and visual experience, under the influence of distinct connectivity patterns.

Purpose: Sensory-substitution devices (SSDs) provide auditory or tactile representations of visual information. These devices often generate unpleasant sensations and mostly lack color information. We present here a novel SSD aimed at addressing these issues. Methods: We developed the EyeMusic, a novel visual-to-auditory SSD for the blind, providing both shape and color information. Our design uses musical notes on a pentatonic scale generated by natural instruments to convey the visual information in a pleasant manner. A short behavioral protocol was utilized to train the blind to extract shape and color information, and test their acquired abilities. Finally, we conducted a survey and a comparison task to assess the pleasantness of the generated auditory stimuli. Results: We show that basic shape and color information can be decoded from the generated auditory stimuli. High performance levels were achieved by all participants following as little as 2-3 hours of training. Furthermore, we show that users indeed found the stimuli pleasant and potentially tolerable for prolonged use. Conclusions: The novel EyeMusic algorithm provides an intuitive and relatively pleasant way for the blind to extract shape and color information. We suggest that this might help facilitating visual rehabilitation because of the added functionality and enhanced pleasantness.

Purpose: Independent mobility is one of the most pressing problems facing people who are blind. We present the EyeCane, a new mobility aid aimed at increasing perception of environment beyond what is provided by the traditional White Cane for tasks such as distance estimation, navigation and obstacle detection. Methods:The "EyeCane" enhances the traditional White Cane by using tactile and auditory output to increase detectable distance and angles. It circumvents the technical pitfalls of other devices, such as weight, short battery life, complex interface schemes, and slow learning curve. It implements multiple beams to enables detection of obstacles at different heights, and narrow beams to provide active sensing that can potentially increase the user's spatial perception of the environment. Participants were tasked with using the EyeCane for several basic tasks with minimal training. Results: Blind and blindfolded-sighted participants were able to use the EyeCane successfully for distance estimation, simple navigation and simple obstacle detection after only several minutes of training. Conclusions: These results demonstrate the EyeCane's potential for mobility rehabilitation. The short training time is especially important since available mobility training resources are limited, not always available, and can be quite expensive and/or entail long waiting periods.

Visual-to-auditory sensory-substitution devices allow users to perceive a visual image using sound. Using a motor-learning task, we found that new sensory-motor information was generalized across sensory modalities. We imposed a rotation when participants reached to visual targets, and found that not only seeing, but also hearing the location of targets via a sensory-substitution device resulted in biased movements. When the rotation was removed, aftereffects occurred whether the location of targets was seen or heard. Our findings demonstrate that sensory-motor learning was not sensory-modality-specific. We conclude that novel sensory-motor information can be transferred between sensory modalities.

Graphical virtual environments are currently far from accessible to blind users as their content is mostly visual. This is especially unfortunate as these environments hold great potential for this population for purposes such as safe orientation, education, and entertainment. Previous tools have increased accessibility but there is still a long way to go. Visual-to-audio Sensory-Substitution-Devices (SSDs) can increase accessibility generically by sonifying on-screen content regardless of the specific environment and offer increased accessibility without the use of expensive dedicated peripherals like electrode/vibrator arrays. Using SSDs virtually utilizes similar skills as when using them in the real world, enabling both training on the device and training on environments virtually before real-world visits. This could enable more complex, standardized and autonomous SSD training and new insights into multisensory interaction and the visually-deprived brain. However, whether congenitally blind users, who have never experienced virtual environments, will be able to use this information for successful perception and interaction within them is currently unclear.We tested this using the EyeMusic SSD, which conveys whole-scene visual information, to perform virtual tasks otherwise impossible without vision. Congenitally blind users had to navigate virtual environments and find doors, differentiate between them based on their features (Experiment1:task1) and surroundings (Experiment1:task2) and walk through them; these tasks were accomplished with a 95% and 97% success rate, respectively. We further explored the reactions of congenitally blind users during their first interaction with a more complex virtual environment than in the previous tasks–walking down a virtual street, recognizing different features of houses and trees, navigating to cross-walks, etc. Users reacted enthusiastically and reported feeling immersed within the environment. They highlighted the potential usefulness of such environments for understanding what visual scenes are supposed to look like and their potential for complex training and suggested many future environments they wished to experience.

Visual sensory substitution devices (SSDs) use sound or touch to convey information that is normally perceived by vision. The primary focus of prior research using SSDs was the perceptual components of learning to use SSDs and their neural correlates. However, sensorimotor integration is critical in the effort to make SSDs relevant for everyday tasks, like grabbing a cup of coffee efficiently. The purpose of this study was to test the use of a novel visual-to-auditory SSD to guide a fast reaching movement. Methods: Using sound, the SSD device relays location, shape and color information. Participants were asked to make fast reaching movements to targets presented by the SSD. Results: After only a short practice session, blindfolded sighted participants performed fast and accurate movements to presented targets, which did not differ significantly from movements performed with visual feedback in terms of movement time, peak speed, and path length. A small but significant difference was found between the endpoint accuracy of movements under the two feedback conditions; remarkably, in both cases the average error was smaller than 0.5 cm. Conclusions: Our findings combine with previous brain-imaging studies to support a theory of a modality-independent representation of spatial information. Task-specificity, rather than modality-specificity, of brain functions is crucially important for the rehabilitative use of SSDs in the blind and the visually impaired. We present the first direct comparison between movement trajectories performed with an SSD and ones performed under visual guidance. The accuracy level reached in this study demonstrates the potential applicability of using the visual-to-auditory SSD for performance of daily tasks which require fast, accurate reaching movements, and indicates a potential for rehabilitative use of the device.

In early blind individuals, brain activation by a variety of nonperceptual cognitive tasks extends to the visual cortex, while in the sighted it is restricted to supramodal association areas. We hypothesized that such activation results from the integration of different sectors of the visual cortex into typical task-dependent networks. We tested this hypothesis with fMRI in blind and sighted subjects using tasks assessing speech comprehension, incidental long-term memory and both verbal and nonverbal executive control, in addition to collecting resting-state data. All tasks activated the visual cortex in blind relative to sighted subjects, which enabled its segmentation according to task sensitivity. We then assessed the unique brain-scale functional connectivity of the segmented areas during resting state. Language-related seeds were preferentially connected to frontal and temporal language areas; the seed derived from the executive task was connected to the right dorsal frontoparietal executive network; and the memory-related seed was uniquely connected to mesial frontoparietal areas involved in episodic memory retrieval. Thus, using a broad set of language, executive, and memory tasks in the same subjects, combined with resting state connectivity, we demonstrate the selective integration of different patches of the visual cortex into brain-scale networks with distinct localization, lateralization, and functional roles.