Development of a Digital Spelled-Speech Reading Machine for the Blind

This machine uses the one-to-one correspondence between spelled-speech utterances and the printed alphabet symbols. Letter recognition was done by first extracting essential features from the information picked up by a photocell scanner and then matching these features with a stored set of data. In order to reduce the amount of memory required to generate letter sounds, redundant phonemes were eliminated and a selected set of basic phonemes was extracted by a segmentation process. Letter sounds were then synthesized by concatenation of these basic phonemes. Also vowels and vowel-like sounds have quasi-periodic waveforms. These sounds were reproduced satisfactorily by repeating over and over again a pitch period extracted from the original waveforms. These algorithms of letter and phoneme synthesis offer considerable saving of memory space and cost in constructing a digital spelled-speech reading machine for the blind. Further reduction in memory storage was accomplished by an encoding scheme. For the experiments, a computer was used to synthesize the letter sounds and to simulate this machine. Experimental results indicated that blind subjects could read spelled sentences between 60 and 70 words/m with 90-percent correct intelligibility after only 1 h of contact with the letter sounds.