Deficient central mechanisms in tinnitus: Exploring the impact on speech comprehension and executive functions

Many individuals with chronic subjective tinnitus report significant problems in comprehending speech in adverse listening situations. A large body of studies has provided evidence to support the notion that deficits in speech-in-noise (SIN) are prevalent in the tinnitus population, while some studies have challenged these findings. Elemental auditory perception is usually only minimally or not impaired. In addition, deficits in cognitive functions, particularly executive functions, have also been observed in individuals with tinnitus. Given these previous findings, we theorize that deficient central mechanisms may be responsible for the reported speech comprehension problems in tinnitus. 25 participants suffering from chronic subjective tinnitus and 25 control participants, between 23 and 58 years of age, were examined in a cross-sectional design. The groups were case-matched for age, sex, education, and hearing loss. A large audiometric battery was used ranging from threshold and supra-threshold tasks to spoken sentence level speech tasks. Additionally, four cognitive tests were performed, primarily covering the area of executive functions. Tinnitometry and tinnitus-related questionnaires were applied to complement sample description and allow for secondary analyses. We hypothesized that tinnitus participants score lower in complex speech comprehension tasks and executive function tasks compared to healthy controls, while no group differences in elementary audiometric tasks were expected. As expected, individuals with chronic subjective tinnitus scored lower in the SIN and gated speech task, while there were no differences in the basic speech recognition threshold task and the other elementary auditory perception tasks. The cognitive tests revealed clear deficits in interference control in the Stroop task, but not in the Flanker task, in the tinnitus group. There were no differences in inhibition or working memory tasks. Our results clearly delineate differences between tinnitus individuals and control participants in two tests on speech intelligibility under adverse listening conditions. Further, the poorer performance in a task of interference control in individuals with tinnitus points towards an impaired central executive control in individuals with tinnitus. Taken together, our (partly) exploratory study provides novel evidence to the view that deficient central executive system in individuals with tinnitus probably account for impaired speech comprehension.