Stability of phoneme-related potentials across testing sessions and stimulus presentation conditions
ObjectivesObjective and ecologically valid measures of speech processing can complement conventional audiologic assessments. Phoneme-related potentials (PRPs), derived by averaging listeners electroencephalography (EEG) responses time-locked to phonemes in continuous speech, have emerged as a promising approach for capturing cortical processing of speech in naturalistic listening conditions. Importantly, PRPs reveal speech perception challenges even when conventional audiograms are clinically normal, positioning them as a promising neural marker for suprathreshold listening difficulties that standard audiometry often misses. As a critical step toward clinical translation, this study examined the extent to which PRP-derived measures remain stable across real-world contexts relevant to clinical implementation, including monaural versus binaural presentation, stimulus intensity level, and repeated testing sessions. The study also assessed cortical tracking of lower-level speech acoustics to determine whether the PRP findings could be attributed to acoustic processing. DesignEEG was recorded from 18 young adults with normal hearing as they listened to audiobook speech presented monaurally or binaurally at 60 or 75 dB across two sessions separated by approximately one week. Neural differentiation of phoneme manner-of-articulation classes (vowels, nasals/approximants, fricatives, and stops) in PRPs was quantified using two measures: an F-statistic reflecting between-manner relative to within-manner variability, and classification accuracy from a machine-learning model trained to predict manner class from PRPs. Temporal response function modeling assessed neural tracking of continuous acoustic envelope and onset features of the audiobook speech. ResultsNeither PRP-derived measure of manner differentiation showed significant effects of session, presentation modality, intensity level, or their interactions. Intraclass correlation analyses further indicated moderate-to-good reliability across all three factors. In contrast, neural tracking of the acoustic envelope and acoustic onsets was stronger under binaural than monaural presentation, with binaural presentation eliciting more pronounced cortical responses to the envelope. ConclusionsPRP-derived measures remained relatively stable across modest procedural variations that are common in clinical testing contexts, positioning PRPs as a potent objective index of naturalistic speech processing. This stability may reflect cortical processing of abstract, linguistically relevant speech categories and suggest that PRPs provide complementary information beyond audiologic assessments of peripheral auditory functions and EEG measures that primarily capture lower-level acoustic processing.