The Effects Of Adverse Listening Conditions Of The Subcortical Neural Encoding Of Speech Stimuli In Normal Hearing Adults

Biomarkers of Peripheral and Central Auditory System Integrity and Function

In hearing impaired patients, neurophysiological measurements are becoming increasingly relevant for diagnostic work-up, therapy indication and treatment monitoring. Objective measures, so-called biomarkers, can help to assess the integrity and function of the peripheral and central auditory system. There are a range of different measurement methods and techniques used in this context. These range from electrophysiological recordings (either with conventional measuring electrodes or, in case of cochlear implant recipients, directly with the implant electrode) to advanced imaging techniques (including magnetic resonance imaging changes to alterations in light absorption when using functional near-infrared spectroscopy). We expect these biomarkers to facilitate therapeutic indication and counselling of patients as well as to provide monitoring tools during (e.g. during cochlear implant insertion) and after therapy (i.e. in the rehabilitation phase).

The Effects of Adverse Listening Conditions of the Subcortical Neural Encoding of Speech Stimuli in Normal-hearing Adults

Objectives: To determine the difference in the effects of background noise and reverberation on the sub-cortical neural encoding of the speech stimulus /u/ using the Frequency Following Response (FFR). Energy related to both the fundamental frequency as well as first formant of the stimulus preserved in the FFR was measured in order to better understand the breakdown of speech in adverse listening conditions . Design: The FFR was recorded to 6 normal hearing adults (aged 24-25 years) in response to the vowel stimulus /u/. Each subject underwent two test sessions. The first session recorded the response to the stimulus in the presence of three levels of reverberation as well as a quiet condition involving no reverberation. The second session recorded the response to the stimulus in the presence of three levels of background noise as well as a quiet or no noise condition. Temporal waveforms, FFTs, and individual amplitude data for both F0 and F1 were generated for each test condition. Results: As expected, as the severity of the condition worsened, the response energy at the F0 decreased. This was seen for both the background noise and reverberation test conditions. In contrast, there were some differences in F1 encoding that occurred as a function of type of adverse listening condition. As expected, the energy at the F1 decreased as background noise condition worsened. However, the energy at the F1 increased as the reverberation condition worsened. This was an unexpected finding. The variability in the data, as reflected in the standard deviation values, was fairly consistent across all test conditions except for F1 data of reverberation. This change in variability could have played a role in the unexpected finding for that condition. Conclusion: The results of the current study suggest that degraded neural encoding abilities at the F0 and first formant may play a role in the speech perception difficulties individuals with sensorineural hearing loss experience.

Descending Control in the Auditory System