gms | German Medical Science

Hearing loss, aging-related changes in central auditory processes, and cognitive declines are the main causes of speech-understanding deficits in the older adults [1], [2]. Auditory training may enhance the brain processes related to speech identification and consequently improve behavioural performance [3], [4]. Yet, it is still not clear at which level the training is effective. One opportunity is to disentangle the multi-modal bottom-up and top-down neural mechanism contributing to changes in the auditory cortex. In this study, we are investigating how speech perception and related brain responses have changed after an auditory training intervention in older listeners. Here, we are presenting the experimental design and preliminary data.

Healthy older adults (60–90 years) were participating in a four-week training intervention. They had normal hearing for their age or mild to moderate hearing loss, with or without Hearing Aids. In a crossover designed study with repeated measures the participants performed two different training sets: First, an identification set (bottom-up) consisted of nonsense consonant-vowel-consonant syllables (CvvC) [5]. The second set used sentence repetitions (top-down) [6]. Both sets were presented in varying background noise in five training sessions each. Brain responses were recorded with EEG before, in between the sets, and after the training, as well as after a six weeks retention periode. Two pairs of syllables (CvvC) were used to elicit the brain response: MAAM-MAAN and NAAM-NAAN. We were recording the Mismatch Negativity (MMN) responses indicating the automatic discrimination of differences in the syllable offset. The behavioral outcome in speech recognition in noise was tested with QuickSIN and BKBSIN (pre, post, longterm). These tests involved different levels of cognitive contributions. We expected that differences between both tests indicate changes on different level of processing.

In all participants the syllable stimuli elicited clear auditory evoked responses. A novelty of our approach is demonstrating MMN responses to deviation of the ending consonant. A strong MMN is elicited for a deviation in syllables with the same onset and offset. However, when onset and offset consonant were different, the MMN response was strongly attenuated. These findings indicate that the mismatch in the ending consonant depends on the context of the leading consonant of the CvvC syllable. The results contribute to the discussion whether the MMN indicates the listeners ability in discriminating between phonological items or the complete syllable and may help to answer the question at which level training may impact on the underlying brain processes.