There is a need for adaptive technology to enhance indoor wayfinding by visually-impaired people. To address this need, we have developed and tested a Digital Sign System. The hardware and software consist of digitally-encoded signs widely distributed throughout a building, a handheld sign-reader based on an infrared camera, image-processing software, and a talking digital map running on a mobile device. Four groups of subjects—blind, low vision, blindfolded sighted, and normally sighted controls—were evaluated on three navigation tasks. The results demonstrate that the technology can be used reliably in retrieving information from the signs during active mobility, in finding nearby points of interest, and following routes in a building from a starting location to a destination. The visually impaired subjects accurately and independently completed the navigation tasks, but took substantially longer than normally sighted controls. This fully functional prototype system demonstrates the feasibility of technology enabling independent indoor navigation by people with visual impairment.

Most people with low vision require magnification to read. A magnifier's field of view often contains only a few letters at a time. Page navigation is the process by which the reader moves the magnifier from word to word, and from the end of one line to the beginning of the next line. Page navigation takes time and reduces reading speed. The major questions addressed in this paper are: (1) What role does page navigation play in limiting reading speed? and (2) Are the window width requirements for reading (number of characters in the field for a criterion performance level) increased by the need for page navigation? We measured the reading speeds of three normal-vision and seven low-vision subjects in two ways: with drifting-text requiring no page navigation, and with a closed-circuit TV (CCTV) magnifier which required page navigation. We built special hardware to record the location of the CCTV's magnified field in the text. These recordings were used to separate forward-reading time (left-to-right movement through the text) from retrace time (navigational movement). For normal-vision subjects, forward-reading and retrace times were about equal. For low-vision subjects, retrace times were shorter than forward-reading times, indicating that the forward-reading performance was limited by visual, not navigational, demands. The retrace time did have an impact, however, ranging from 17 to 50% of the overall time. The window requirements for reading with page navigation (CCTV) were larger than those for reading without page navigation (drifting-text). The difference was more than a factor of three for normal-vision subjects and close to a factor of two for low-vision subjects (10 characters for CCTV vs 5.2 characters for drifting-text for 85% of maximum reading speed.

We created a sequential ideal-observer model that could address the question, How much of letter identification performance and its change with eccentricity can be accounted for by preneural factors? The ideal-observer model takes into account preneural factors including the stimulus rendering properties of a CRT display, the optical imaging quality of the eye, and photon capture and sampling characteristics of the cones. We validated the formulation of the model by comparing its performance on simple psychophysical tasks with that of previous sequential ideal-observer models. The model was used to study properties of the image rendering of letters. For example, the model's identification of high-resolution letters (i.e., many pixels per letter), but not low-resolution letters, is largely immune to changes in pixel width. We compared human and ideal-observer letter-identification acuity for the lowercase alphabet at 0 degrees, 5 degrees, and 20 retinal eccentricity. Acuity of the ideal observer for high-contrast letters is approximately seven times better than that of the human observers at 0 degrees. Acuity decreased with eccentricity more rapidly for human observers than for the ideal observer such that the thresholds differed by a factor of 50 at 20 degrees. A decrease in stimulus duration from 100 to 33 ms resulted in no decrease in relative threshold size between the human and ideal observers at all eccentricities, indicating that humans effectively integrate stimulus information over this range. Decreasing contrast from 75% to 25%, however, reduced the difference in acuities twofold at all eccentricities between humans and the ideal-observer model, consistent with the presence a compressive nonlinearity only in the human observers. The gap between human and ideal acuity in central vision means that there are substantial limitations in human letter recognition beyond the stage of photoreceptor sampling. The increasing performance gap between human and ideal-observer performance with eccentricity implicates an increasing role of neural limitations with eccentricity in limiting human letter identification.

The proliferation of mobile devices and the emergence of wireless location-based services has generated consumer demand for availability of GPS in urban and indoor environments. This demand calls for enhanced GPS algorithms that accommodate high degrees of signal attenuation and multipath effects unique to the ''urban channel.'' This paper overviews the market for location-based services and discusses algorithmic innovations that address challenges posed by urban environments.

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