gms | German Medical Science

Introduction: The primary aim of cochlear implantation is usually an improved understanding of speech, especially speech understanding in noise as this is the most common and yet challenging auditory condition in real world. In order to assess the improvements over time, the OLSA matrix test and Göttingen sentence test are the most common speech recognition tests. In recent years, Smits and colleagues developed an easy-to-use test, which is based on mono-syllabic digit triplets presented in noise [1]. Advantages of the digit triplet test (DTT) are that digits are highly familiar word material, they are easy to learn also for foreigners, there is only a small learning effect and the closed set response limits the effect of top-down processes. All these advantages make the DTT a perfect candidate for testing speech recognition in CI patients. The objective of the current study is to test the validity (reliability over time) of the DTT. Furthermore, it has been shown that the listening effort for the OLSA sentence test in noise has been rated high, especially by listeners with hearing impairment (e.g., [2]). Thus, the second objective is to evaluate the listening effort for the DTT.

Methods: In subjects implanted with a cochlear implant from Cochlear Ltd. we measured the DTT and the OLSA in noise across three time points (3, 4.5 and 6 months after first switch-on) to evaluate whether test scores change comparably over time. To evaluate listening effort we implemented a dual-task paradigm in which the subject had to perform the DTT and the OLSA while simultaneously reacting as fast as possible to a secondary task of a light switching on in front of them. The more difficult the primary task of performing the sentence test becomes the less capacity the brain has to fulfill the secondary task and reaction times should increase. In addition, a questionnaire to assess listening effort is analyzed.

Results and discussion: Preliminary results from this ongoing study show a better signal-to-noise ratio (SNR) in the DTT compared to the OLSA, which may result from the higher cognitive load of the OLSA making it the more difficult speech test. However, the SNRs decrease by a similar amount from the first to the third visit suggesting that both, DTT and OLSA, similarly reflect the improvement in speech understanding in noise over time. The analysis of the reaction times as well as the questionnaire show that the listening effort for the DTT is lower than for the OLSA and that the listening effort increases with increasing difficulty of the SNR.