Effect of word familiarity on word intelligibility of four continuous words under long-path echo conditions

The massive earthquake that occurred on 11 March 2011 in Japan demonstrated that the intelligibility of speech presented over mass notification sound systems is often significantly degraded by long-path echoes. This study examines the effect of word familiarity on speech intelligibility in the presence of long-path echoes, in order to increase speech intelligibility in such systems. We performed two experiments using sets of four sequentially connected words (quadruplets), in place of an actual sentence. In Experiment 1, we investigated word intelligibility in the presence of simulated long-path echoes for quadruplets consisting of words with the same word familiarity rank. The results indicated that the intelligibility of high-familiarity words is higher than that of low-familiarity words, irrespective of the number of simulated long-path echoes. In Experiment 2, quadruplets with mixed word familiarity were used to investigate intelligibility under more realistic conditions. The results of Experiment 2 demonstrate that the intelligibility of high-familiarity words is higher than that of low-familiarity words under long-path echo conditions, even when high- and low-familiarity words coexist in one quadruplet. These facts show that high-familiarity words are more robust against the influence of long-path echoes than low-familiarity words, strongly suggesting that announcements presented from mass notification sound systems should consist of high familiarity words as much as possible.