Development of the Continuous Number Identification Test (CNIT): feasibility of dynamic assessment of speech intelligibility.

The present study was motivated by a need for a speech intelligibility test capable of indexing dynamic changes in the environment and adaptive processing in hearing aids. The Continuous Number Identification Test (CNIT) was developed to meet these aims. From one location in the free field, speech was presented in noise (∼2 words/s) with a 100-ms inter-word interval. On average, every fourth word was a target digit and all other words were monosyllabic words. Non-numeric words had a fixed presentation level such that the dominant signal-to-noise-ratio (SNR) was held at +6 dB SNR relative to background maskers. To prevent ceiling effects, however, targets were presented at a user-specific SNR, determined by an initial adaptive-tracking procedure that estimated the 79.4% speech reception threshold. Ten normal-hearing listeners participated. The CNIT showed comparable psychometric qualities of other established speech tests for long time scales (Exp. 1). Target-location changes did not affect performance on the CNIT (Exp. 2), but the test did show high temporal resolution in assessing sudden changes to SNR (Exp. 3). The CNIT is highly customisable, and the initial experiments tested feasibility of its primary features which set it apart from currently available speech-in-noise tests.