Tracking of Noise Tolerance Test Outcomes With the International Speech Test Signal

The purpose of this study was to assess whether using the International Speech Test Signal (ISTS) as a nonmeaningful target signal changes listener outcomes on the Tracking of Noise Tolerance (TNT) test and their relationship to hearing loss and neuroelectrophysiological indices of central inhibition.

Single-blind mixed design conducted in 23 normal-hearing (NH) and 16 hearing-impaired (HI) older adults with moderate-to-severe degrees of sensorineural hearing loss. Participants performed a modified version of the TNT test where they were asked to react to a dynamic background noise while listening to the ISTS target stimulus. Test performance was characterized by average TNT test noise acceptance (TNT_Ave) and by the average difference between peaks and valleys in tracked noise level tracings (excursion). All listeners had previously performed the TNT test using English speech passages as target signals. Cortical sensory gating magnitudes were also measured from these listeners as electrophysiological indices of central inhibition.

Whereas NH listeners tolerated significantly less noise when performing the TNT test with ISTS relative to English speech targets, type of target signal had no effect on TNT_Ave scores in HI listeners. Conversely, HI listeners exhibited significantly greater excursion in their tracked noise levels when tested with the ISTS compared to English passages, but target type did not affect excursion in NH listeners. Regardless of target type or hearing group, TNT excursion was strongly predicted by listeners' bilateral four-frequency pure-tone averages. As previously observed for the English TNT, sensory gating magnitudes of the N1-P2 component negatively predicted TNT excursion scores measured using the ISTS target after accounting for listener age and hearing thresholds. In addition, noise acceptance (TNT_Ave) outcomes for ISTS targets were positively predicted by cortical gating magnitudes of the P1 component.

Replacing meaningful English speech with ISTS targets affected listener performance on the TNT test differently in NH and HI listeners. Comparing TNT outcomes for nonmeaningful and meaningful speech signals may be useful for gaining insight into the acoustic and nonacoustic (e.g., central/contextual) factors that affect listeners' dynamic reactivity to changing levels of background noise.