Spoken word intelligibility tests under noisy conditions

Word intelligibility under noisy conditions has been regarded as an extremely useful parameter for assessing hearing ability in daily life. However, the familiarity of words used in the test must be controlled because word intelligibility is strongly affected by word familiarity. Moreover, the phonemes that the words contain must be considered because some phonemes are typically unintelligible, especially in noisy conditions. For these reasons, we developed the Familiarity-controlled Word lists 2003 (FW03). The FW03 includes 20 word lists of 50 words each in four familiarity ranks (4000 words in total) for which the entropy of the phoneme occurrence probability was maximized. Subsequently, we developed FW07 to facilitate clinical examinations, such as those required when fitting hearing aids. The number of words in each list was reduced from 50 to 20 in FW07 to reduce the burden imposed on the subject. When using FW07, we recommended that the presentation sound pressure level for each word be adjusted employing the Speech Recognition Threshold (SRT) to reduce the differences between the mean intelligibilities of the 20 word lists in the same familiarity rank. By employing this approach, smaller differences in the mean intelligibility were confirmed in the FW07 lists. This facilitated a comparison of word intelligibility under different conditions without same word repetition.