On the Relation between the Intelligibility and Frequency of Occurrence of English Words

Abstract

The threshold of intelligibility for a word in a wide-spectrum noise is shown to be a decreasing function of the frequency with which the word occurs in general linguistic usage (word frequency). The drop in threshold is about 4.5 db per logarithmic unit of word, although the thresholds for words of given frequency of occurrence are lower for. long words. The effect of restricting the listener''s alternatives in an intelligibility test to a specified number of words is calculated from this relationship. These calculations come within 1 db of published experimental data. Theoretical functions relating intelligibility threshold to word length are also calculated from the word-frequency effect, on the assumption that listeners can discriminate the length of a word at levels too low for it to be identified. These functions are in general agreement with the experimental results. Implications for intelligibility testing procedures are discussed.