Stability of Early Auditory Evoked Potential Components Over Extended Test-Retest Intervals in Young Adults

Peripheral deficits and phase-locking declines in aging adults

Age-related difficulties in speech understanding may arise from a decrease in the neural representation of speech sounds. A loss of outer hair cells or decrease in auditory nerve fibers may lead to a loss of temporal precision that can affect speech clarity. This study's purpose was to evaluate the peripheral contributors to phase-locking strength, a measure of temporal precision, in recordings to a sustained vowel in 30 younger and 30 older listeners with normal to near normal audiometric thresholds. Thresholds were obtained for pure tones and distortion-product otoacoustic emissions (DPOAEs). Auditory brainstem responses (ABRs) were recorded in quiet and in three levels of continuous white noise (+30, +20, and +10 dB SNR). Absolute amplitudes and latencies of Wave I in quiet and of Wave V across presentation conditions, in addition to the slope of Wave V amplitude and latency changes in noise, were calculated from these recordings. Frequency-following responses (FFRs) were recorded to synthesized /ba/ syllables of two durations, 170 and 260 ms, to determine whether age-related phase-locking deficits are more pronounced for stimuli that are sustained for longer durations. Phase locking was calculated for the early and late regions of the steady-state vowel for both syllables. Group differences were found for nearly every measure except for the slopes of Wave V latency and amplitude changes in noise. We found that outer hair cell function (DPOAEs) contributed to the variance in phase locking. However, the ABR and FFR differences were present after covarying for DPOAEs, suggesting the existence of temporal processing deficits in older listeners that are somewhat independent of outer hair cell function.

Unconstrained multivariate EEG decoding can help detect lexical-semantic processing in individual children

In conditions such as minimally-verbal autism, standard assessments of language comprehension are often unreliable. Given the known heterogeneity within the autistic population, it is crucial to design tests of semantic comprehension that are sensitive in individuals. Recent efforts to develop neural signals of language comprehension have focused on the N400, a robust marker of lexical-semantic violation at the group level. However, homogeneity of response in individual neurotypical children has not been established. Here, we presented 20 neurotypical children with congruent and incongruent visual animations and spoken sentences while measuring their neural response using electroencephalography (EEG). Despite robust group-level responses, we found high inter-individual variability in response to lexico-semantic anomalies. To overcome this, we analysed our data using temporally and spatially unconstrained multivariate pattern analyses (MVPA), supplemented by descriptive analyses to examine the timecourse, topography, and strength of the effect. Our results show that neurotypical children exhibit heterogenous responses to lexical-semantic violation, implying that any application to heterogenous disorders such as autism spectrum disorder will require individual-subject analyses that are robust to variation in topology and timecourse of neural responses.