LM202 - Update on the TNT: A Profiling, Validation, and Fine-Tuning Tool

Abstract:
The Tracking of Noise Tolerance (TNT) test was proposed as an efficient and reliable means to estimate noise acceptance while instructing the listeners to maintain over 90 percent speech understanding. It has been used to profile a listener and quantify the benefit of hearing aid features. Recently, we have compensated for the hearing loss of the listener while conducting the test. We will review the studies conducted using this tool, update the audience on the new additions to the test, and summarize how the test may be used for different clinical purposes.

Summary:
The Tracking of Noise Tolerance (TNT) test was first proposed in 2017 by our research group to study the dynamic changes in noise acceptance for fixed loud speech over a two-minute period. It was inspired by the Acceptable Noise Level (ANL) test but different in that the TNT uses fixed loud speech (75 and 82 dB SPL) and listeners track the maximum noise level they can accept while understanding more than 90 percent of the words in the passage. The difference between the average noise level and the fixed speech level is the TNT, or how much noise the listener can accept. Furthermore, the TNT has several equivalated passages that can be used interchangeably. These procedural differences likely explain the excellent test-retest reliability of the measure (95 percent confidence interval < 2 dB within-session and < 4 dB between-session).

The TNT test has been used to validate the benefits of hearing aid features such as directional microphones, noise reduction algorithm, WDRC processing, and split processing. In addition, there was moderate correlation between the aided TNT and listener hearing aid satisfaction in noise. More recently, we used the TNT speech materials to evaluate subjective and objective speech understanding. We observed that while normal hearing (NH) listeners judged subjective speech understanding similarly as objective understanding, hearing impaired (HI) listeners perceived that they understood more than they actually did when not wearing hearing aids. We validated that the valleys of the TNT tracking correspond to about 90 percent subjective speech understanding, while the peaks correspond to around 40-50 percent subjective speech understanding. We also discovered that listeners used their subjective speech understanding as a means to determine noise acceptance. In conditions where subjective speech understanding is poor ( < 70 percent or so), listeners primarily use subjective speech understanding as the main criterion to determine how much noise they can accept. When the listening conditions improve and their subjective speech understanding improves, their criteria for noise acceptance shift toward a cognitive/emotional basis. These findings will be shared with the audience along with their clinical and technical implications.

In the last year, we furthered the development of the TNT by creating a version of the test that compensates for the degree of hearing loss of the listener. The hearing loss compensated version of the TNT (c-TNT) takes the hearing loss of the listener and applies the NAL-NL2 fitting formula to calculate necessary gain for the 75 dB fixed speech input to ensure that the calculated speech intelligibility index (SII) for the test materials would yield 100 percent speech understanding in quiet. Our limited data to date is that compensation improves noise acceptance on some but worsens noise acceptance in others. Despite the compensation, the TNT of HI listeners were still poorer than those of NH listeners. We will share these findings with the audience along with their clinical implications. A protocol will be outlined where the interested clinicians may follow to use the TNT effectively.

Brief Summary of Clinical Takeaways:
Clinicians will leave with knowledge on how to measure and use noise acceptance information to predict potential hearing aid acceptance (and required features), fine-tune parameters/features on the hearing aids, and validate the efficacy of the hearing aid fitting and/or specific features.