Automated directory listing retrieval system based on isolated word recognition

Automated directory listing retrieval has been a goal of the Bell System and others for a long time. Recent attempts at implementing such a system relied on button pushing on the part of the user. Since the Touch-Tone ® keyboard does not contain a unique key corresponding to each letter of the alphabet, the button pushing system had some drawbacks. In an attempt to alleviate these problems and to provide a more natural form of communication for the user, the use of spoken spelled names was proposed in place of pushing buttons. An early form of this directory listing retrieval system was a speaker trained system (i.e., it had to be trained to each user individually) and it used a simplified directory search algorithm. Subsequent improvements and modifications to both the recognition algorithm and the directory search procedure have led to the current implementation in which the overall system is speaker independent and can automatically find the name (or names) in the directory which provides the best acoustic match to the spoken name. The new system can automatically detect and correct simple (i.e., single letter) anomalies in the spelling of the name, including letter substitutions, inversions, deletions, and insertions. If a conflict in the detected name occurs (e.g., 2 or more names with the same or close acoustic distance scores), the system automatically requests additional information to help resolve the ambiguity. In evaluational tests on an 18 000 name Bell Laboratories directory, the directory listing retrieval system found the unique correct name in 98.3 percent of the trials, on average, even though the acoustic recognizer provided the correct letters only about 70 percent of the time.