The adaptive modified rhyme test

Abstract

This paper discusses an application of the adaptive maximum-likelihood procedure (MLP) [Watson and Pelli, Percept. Psychophys. 33, 113–120 (1983)] to speech intelligibility measurements conducted with the modified rhyme test (MRT) [House et al., J. Acoust. Soc. Am. 37, 158–166 (1965)]. The MLP procedure allows the experimenter to preset the target intelligibility at any value and determine the corresponding speech-to-noise (S/N) ratio. This makes it an efficient tool for estimating the change in the S/N ratio required to maintain identical intelligibility in different noise conditions of the communication channel. The MLP-MRT was tested on a group of 12 listeners. The S/N ratio corresponding to intelligibilities of 50%, 70%, and 88% was determined in five test runs of 30 items each. Subsequently, the S/N ratios estimated by the adaptive procedure were verified by measuring the intelligibility scores by a nonadaptive method. Results showed that intelligibility scores obtained by the nonadaptive method differed by less than 5% from the intelligibility preset in the adaptive procedure. [Part of the work was done as a collaborative project between NRC and the Defence and Civil Institute of Environmental Medicine, during the author’s stay with the Acoustics and Signal Processing Group, NRC, Ottawa, Canada.]