A low-resolution visual display showing the distance to nearby objects as a scale of brightness, and positioned close to the eyes without focussing optics, was sufficient to allow sighted participants to navigate a small obstacle course. All participants could use depth-based information to locate and avoid obstacles, and overall task performance appeared to improve at a logarithmic rate. Walking speed was shown to increase across trials without an increase in the number of collisions, suggesting that participants were rapidly adapting to the novel visuo-spatial display. Logarithmic adaptation rates are seen in visuo-motor tasks where participants learn to use an altered visual display, such as prismatic lenses, to walk around obstacles or manually reach for targets 
. Such rates are indicative of neural plasticity underpinning learning and adaptation. The high learning rates presented here help to show that depth-based imaging is capable of generating an intuitive visual field, which would be an advantage for an assistive device developed for people advanced in age and unfamiliar with such technology.
Situational awareness generally improves with a wide field of view, and while the LED displays in this experiment provided approximately 120 degrees of horizontal vision, the input image from the camera was restricted to under 60 degrees. In order to present a visible image on the display that was in proportion to the size and scale of objects in the real world, the vertical angle had to be limited to 26 degrees. Participants responded to this reduced vertical field of view by adopting a behaviour of walking with their heads angled downwards to better see the obstacles. A consequence of the limited visual field was that a high proportion of collisions were made with obstacles that they appeared to have passed were still by their side. Further iterations of the apparatus would clearly benefit from a wider horizontal and vertical input image.
Head mounted displays can often cause eye strain as they force the visual system to focus at a fixed depth. The displays in these experiments were unfocussable and when asked participants did not report any discomfort despite wearing the goggles continuously for up to thirty minutes. The distance between the eye and the display in this study was under 3 cm, which is too close to trigger accommodation, thus participants appeared not to attempt to focus on the display but rather looked through it. This behaviour was encouraged by creating a binocular display that allowed the eyes to fuse the image at a comfortable distance. However, even through this blurred view, it was easy for the participants of this study to identify the boundaries of objects and their approximate size and position.
Using a similar low-resolution and near positioned display, blind and partially-sighted individuals were able to see and respond to illuminated objects presented throughout their residual visual fields. All sight-impaired individuals were able to perform the head-mounted search task and many of the participants who self-reported that they had no useful residual vision could still complete the task. Predictably, participants with advanced RP (with peripheral vision deficits) were unable to reliably respond to objects presented in the periphery. Conversely, participants with AMD (characterised by a central vision deficit) appeared to have no specific problem detecting targets in any region of their visual fields, including the centre. The close proximity of the display to the eyes did not prevent the participants from finding the targets, nor did it produce symptoms of eye strain over the period of testing.
Having established that healthy controls can use a dynamic low-resolution depth-based display for navigation, and that severely sight-impaired people are able to perform a search task using static visual cues on a similar display, the next stage is to establish whether this technique can improve obstacle avoidance in blind or partially-sighted individuals. Severely sight-impaired individuals are often highly skilled at detecting and tracking object positions by using shadows, reflections and memory. People with macular degeneration often have sufficient peripheral vision in good light to detect obstacles while walking. In order to make a proper estimate of any benefit that this type of display may add, it would be necessary to combine depth-based information with their remaining vision using, for instance, a transparent see-through LED display.
In unquantified discussions with sight impaired individuals using the depth-based version of display, many were able to quickly and accurately detect people at a distance of up to 4 metres away. Furthermore, within ten minutes almost all were able to recognise nearby objects such as walls, chairs and their own limbs. This suggests that depth-based imaging may be an easy to learn and highly intuitive form of visual augmentation. For a more detailed assessment of the usefulness of such a wearable display for different severities of sight loss, the classification of visual acuity and visual fields and contrast sensitivity needs to be performed. For instance, contrast sensitivity is often much lower in visual impairments and some individuals may not be able to detect a scale of brightness indicating depth, rather they may see just a binary image (eg. object/no object).
This study provides evidence of the potential to develop a wearable display that can deliver simplified, rapid and usable object detection for the purpose of obstacle avoidance in people with very limited sight. With refinements to the field of view, screen resolution and portability, such a device may be able to provide intuitive visual enhancements through one's residual vision.