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
Two tones of different frequencies alternated successively five times per second. When the difference in frequency was small, the alternation sounded like a continuous up-and-down movement of the pitch. When the difference in frequency was large, the alternation sounded like two unrelated, interrupted tones. The transition point between these two perceptual organizations is called the trill threshold. The trill threshold was measured as a function of frequency for 14 subjects; the results are summarized in Fig. 1.
Rats were trained to stable baselines of lever pressing on a variable intertrial interval continuous nonmatching to sample schedule (CNM) or on an analogous discrimination schedule. Scopolamine reduced accuracy of CNM performance to a similar extent over the three intertrial (retention) intervals: 2.5, 5, and 10 s, results indicating that the drug did not affect the time-dependent process of retention in working memory. When baseline levels of performance accuracy were similar in the CNM and discrimination tasks (but stimulus discriminability was greater in the CNM task), scopolamine reduced accuracy equally in the two procedures. Effects of scopolamine on accuracy of noncorrection trial CNM performance were simulated by reducing stimulus discriminability; however, scopolamine disrupted CNM correction trial performance much more than did reductions in stimulus discriminability. It is concluded that scopolamine's effects on working memory are not limited to possible effects on stimulus discrimination: Scopolamine may also affect retrieval of response rules from reference memory.
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