The function of sentence accents and given/new information in speech processing: different strategies for normal-hearing and hearing-impaired listeners?

Two experiments were carried out to investigate how the correspondence between sentence accentuation and distribution of information is used in human word processing. A forced-choice task with target words embedded in sentences was employed for this purpose. Target words provided either 'given' or 'new' information, and were either accented or unaccented. The subjects had to choose between two words that differed in the last consonant by one phonetic feature (e.g., mouth/mouse). The first experiment involved both normal-hearing and hearing-impaired listeners. A fixed amount of noise was used to reduce the quality of speech for normal-hearing listeners, in order to enable a comparison between the two listener groups. The results of the first experiment showed different processing patterns for normal-hearing and hearing-impaired listeners. The hearing-impaired listeners were more accurate with words that were properly accented for their information value, whereas the normal-hearing subjects were more accurate with accented than unaccented words regardless of their information value. A new group of normal-hearing subjects was tested in a second experiment with speech of more severely reduced quality. The results indicated that, under these circumstances, the normal-hearing listeners changed their strategy and also showed an interaction between information value and accent. It seems that, as speech becomes less intelligible, listeners depend increasingly on linguistic expectations stemming from the correlation between information value and accentuation.