gms | German Medical Science

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. During regular follow up visits in the clinic the progress of speech understanding in noise is commonly measured with the OLSA matrix test. However, for CI patients this sentence test is challenging, frustrating and subjectively requires a high level of listening effort. In recent years, Smits et al. developed an easy-to-use test, which is based on mono-syllabic digit triplets presented in noise [1]. Advantages of the DTT are that digits are highly familiar, they are easy to learn with 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. In this study we aimed to compare speech reception thresholds (SRTs) and their improvement over time between the DTT and the OLSA matrix test. A second objective was to evaluate the listening effort in both speech tests, whether the DTT is less demanding than the OLSA.

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 (primary task) while simultaneously reacting as fast as possible to a light switching on in front of them (secondary task). The more difficult the primary task of performing the sentence test becomes the less capacity the brain has to execute the secondary task. Therefore, reaction times should increase. In addition, a questionnaire to assess listening effort was implemented.

The DTT shows a significantly better SRT than the OLSA. Along the timeline from the 3-month to the 6-month-visit, there is no significant improvement in the DTT threshold whereas subjects improved significantly in the OLSA from the first to the third visit. A possible explanation could be that the DTT already is at the lower threshold limit at the 3-month follow up due to the simplicity of the task. The listening effort measured with the dual-task paradigm resulted in no significant difference in the mean reaction times between the DTT and the OLSA. However, during the first visit the reaction times were longer for the OLSA compared to the DTT in most subjects whereas during the third visit they were shorter. That the difficulty and thus, the cognitive load gets larger with a decreasing signal-to-noise ratio (SNR) can be seen in the increasing reaction times with a more difficult SNR and in the higher reaction times for incorrect trials compared to correct trials. Subjectively, subjects rated the listening effort higher for the OLSA compared to the DTT in the questionnaire.