Abstract :
Many direct-translation reading aids for the blind have been built in the past, employing an auditory output consisting of a combination of tones indicating the black regions in a vertical slice through a letter space, or a tactile output consisting of a raised or vibrating image of the letter shapes. Maximum reading rates obtained by the majority of subjects with these reading aids have been less than 10 correct words per minute, and the cause of this limitation has not been well understood. By analyzing the spatial spectral content of letter patterns, we show here that most of these reading aids have violated the well-known sampling theorem. It is suggested that this may be a significant factor in the observed reading-rate limitation. The design of a reading aid is described based on the conclusions from this analysis of the sampling process, and on recent results from tactile research. With this reading aid a hand-held probe images a vertical section of a letter space onto a 24 × 6 array of photosensors, and the probe is manually moved horizontally across the line of print. The signal from each photosensor controls a tactile stimulator in a corresponding array of 144 stimulators, which are placed on a single finger. In preliminary reading tests with this device, four subjects have all read at rates greater than 10 correct words per minute, and two of the subjects have read at rates greater than 20 correct words per minute.
