The intelligibility of speech as a function of the context of the test materials.

For many years communication engineers have used a psychophysical method called the "articulation test" (2, 3). An announcer reads lists :of syllables, words, or sentences to a group of listeners who report what they hear. The articulation score is the percentage of discrete test units reported correctly by the listeners. This method gives a quantitative evaluation of the performance of a speech communication system. There are three classes of variables involved in an articulation test: the personnel, talkers and listeners; the test materials, syllables, words, sen" tences, or continuous discourse; and the communication equipment, rooms, microphones, amplifiers, radios, earphones, etc. The present paper is ̂ directed toward the second of these three classes of variables, the test materials. The central concern can be stated as follows: Why is a stimulus configuration, a word, heard correctly in one context and incorrectly in another? Three kinds of contexts are explored: (a) context supplied by the knowledge that the test item is one of a small vocabulary of items, (b) context supplied by the items that precede or follow a given item in a word or sentence, and (c) context supplied by the knowl-