Voice Pitch Elicited Frequency Following Response in Chinese Elderlies

Background: Perceptual and electrophysiological studies have found reduced speech discrimination in quiet and noisy environment, delayed neural timing, decreased neural synchrony, and decreased temporal processing ability in elderlies, even those with normal hearing. However, recent studies have also demonstrated that language experience and auditory training enhance the temporal dynamics of sound encoding in the auditory brainstem response. The purpose of this study was to explore the pitch processing ability at the brainstem level in an aging population that has a tonal language background.Method: Mandarin speaking younger (n=12) and older (n=12) adults were recruited for this study. All participants had normal audiometric test results and normal suprathreshold click-evoked auditory brainstem responses (ABR). To record Frequency Following Responses (FFR) elicited by Mandarin lexical tones, two Mandarin Chinese syllables with different fundamental frequency pitch contours (Flat Tone and Falling Tone) were presented at 70 dB SPL. Fundamental frequencies (f0) of both the stimulus and the responses were extracted and compared to individual brainstem responses. Two indices were used to examine different aspects of pitch processing ability at the brainstem level: Pitch Strength and Pitch Correlation. Results: Lexical tone elicited FFR were overall weaker in the older adult group compared to their younger adult counterpart. Measured by Pitch Strength and Pitch Correlation, statistically significant group differences were only found when the tone with a falling f0 (Falling Tone) were used as the stimulus.Conclusion: Results of this study demonstrated that in a tonal language speaking population, pitch processing ability at the brainstem level of older adults are not as strong and robust as their younger counterparts. Findings of this study are consistent with previous reports on brainstem responses of older adults whose native language is English. On the other hand, lexical tone elicited FFRs have been shown to correlate with the length of language exposure. Older adults’ degraded responses in our study may also be due to that, the Mandarin speaking older adults’ long term exposure somewhat counteracted the negative impact on aging and helped maintain, or at least reduced, the degradation rate in their temporal processing capacity at the brainstem level

Envelope-following responses and the effects of cochlear delay

There is great interest in developing clinical applications for phase-locked auditory potentials that are elicited by human speech. A common analysis of vowel-elicited responses is to analyze the envelope-following response (EFR) amplitude at the fundamental frequency (F0) of the eliciting vowel. For this study, we systematically examined the effect of modeled vowel formants on EFR amplitude. EFRs were elicited using a fundamental frequency of 103 Hz, representative of a male speaker’s fundamental frequency. Stimuli consisted of two simultaneously presented sinusoidally amplitude-modulated tones with the same F0. One carrier frequency was fixed at 353 Hz, representing a first formant frequency; the carrier frequency of the other tone, representing a second formant frequency, varied across conditions. At each F0, different distances between the carrier frequencies targeted a range of cochlear phase delays (e.g., 90 to 180°). This study hypothesized that the amplitude of the EFR at the F0 of a complex sound would be affected by the cochlear travel delay related to the acoustic characteristics of the eliciting sound. The findings of this study did not show significant changes in response amplitude across stimulus conditions. Therefore, these results do not indicate that cochlear travel delay has a significant affect on envelope-following responses amplitude

Rapid neural processing of grammatical tone in second language learners

The present dissertation investigates how beginner learners process grammatical tone in a second language and whether their processing is influenced by phonological transfer. Paper I focuses on the acquisition of Swedish grammatical tone by beginner learners from a non-tonal language, German. Results show that non-tonal beginner learners do not process the grammatical regularities of the tones but rather treat them akin to piano tones. A rightwards-going spread of activity in response to pitch difference in Swedish tones possibly indicates a process of tone sensitisation. Papers II to IV investigate how artificial grammatical tone, taught in a word-picture association paradigm, is acquired by German and Swedish learners. The results of paper II show that interspersed mismatches between grammatical tone and picture referents evoke an N400 only for the Swedish learners. Both learner groups produce N400 responses to picture mismatches related to grammatically meaningful vowel changes. While mismatch detection quickly reaches high accuracy rates, tone mismatches are least accurately and most slowly detected in both learner groups. For processing of the grammatical L2 words outside of mismatch contexts, the results of paper III reveal early, preconscious and late, conscious processing in the Swedish learner group within 20 minutes of acquisition (word recognition component, ELAN, LAN, P600). German learners only produce late responses: a P600 within 20 minutes and a LAN after sleep consolidation. The surprisingly rapid emergence of early grammatical ERP components (ELAN, LAN) is attributed to less resource-heavy processing outside of violation contexts. Results of paper IV, finally, indicate that memory trace formation, as visible in the word recognition component at ~50 ms, is only possible at the highest level of formal and functional similarity, that is, for words with falling tone in Swedish participants. Together, the findings emphasise the importance of phonological transfer in the initial stages of second language acquisition and suggest that the earlier the processing, the more important the impact of phonological transfer

Development and significance of the spatial auditory change complex in adult cochlear implant users

Despite their great success, cochlear implants (CIs) are associated with a wide range in speech perception outcomes. Interactions of electrode contacts on the CI array, resulting in impaired transmission of the auditory signal, may contribute to poor outcome in certain individuals. The aim of this thesis was to determine whether the spatial auditory change complex (ACC), an electrophysiological measure of electrode discrimination, could be used to objectively assess electrode independence, with a view to using this as a clinical tool for patient assessment. In a series of experiments, the spatial ACC and behavioural electrode discrimination were measured in adult CI users. It was found that it is feasible to measure the spatial ACC in CI devices from different manufacturers and during the early period after switch-on. There was a strong relationship between objective and behavioural measures of electrode discrimination and in several cases, the development of the spatial ACC preceded accurate behavioural discrimination. Longitudinal measurements revealed that the amplitude of the spatial ACC and behavioural discrimination scores increased significantly over the first 6 to 12 months of CI use, providing evidence for auditory plasticity. The time course of adaptation varied substantially, and was slower and more limited in certain individuals. Speech perception was found to be more consistently related to behavioural measures of electrode discrimination than to the spatial ACC. Increasing stimulus intensity led to a significant increase in the spatial ACC amplitude and behavioural discrimination scores. By altering the recording setup and stimulus characteristics, the efficiency and sensitivity of spatial ACC measurements could be improved. These findings show that the spatial ACC provides a useful measure of electrode independence. It is proposed that these measurements could be used to guide clinical interventions that lead to improved hearing outcome in CI users

Error Signals from the Brain: 7th Mismatch Negativity Conference

The 7th Mismatch Negativity Conference presents the state of the art in methods, theory, and application (basic and clinical research) of the MMN (and related error signals of the brain). Moreover, there will be two pre-conference workshops: one on the design of MMN studies and the analysis and interpretation of MMN data, and one on the visual MMN (with 20 presentations). There will be more than 40 presentations on hot topics of MMN grouped into thirteen symposia, and about 130 poster presentations. Keynote lectures by Kimmo Alho, Angela D. Friederici, and Israel Nelken will round off the program by covering topics related to and beyond MMN