Processing of syllable stress is functionally different from phoneme processing and does not profit from literacy acquisition

Abstract

Speech is characterized by phonemes and prosody. Neurocognitive evidence supports the separate processing of each type of information. Therefore, one might suggest individual development of both pathways. In this study, we examine literacy acquisition in middle childhood. Children become aware of the phonemes in speech at that time and refine phoneme processing when they acquire an alphabetic writing system. We test whether an enhanced sensitivity to phonemes in middle childhood extends to other aspects of the speech signal, such as prosody. To investigate prosodic processing, we used stress priming. Spoken stressed and unstressed syllables (primes) preceded spoken German words with stress on the first syllable (targets). We orthogonally varied stress overlap and phoneme overlap between the primes and onsets of the targets. Lexical decisions and Event-Related Potentials (ERPs) for the targets were obtained for pre-reading preschoolers, reading pupils and adults. The behavioral and ERP results were largely comparable across all groups. The fastest responses were observed when the first syllable of the target word shared stress and phonemes with the preceding prime. ERP stress priming and ERP phoneme priming started 200 ms after the target word onset. Bilateral ERP stress priming was characterized by enhanced ERP amplitudes for stress overlap. Left-lateralized ERP phoneme priming replicates previously observed reduced ERP amplitudes for phoneme overlap. Groups differed in the strength of the behavioral phoneme priming and in the late ERP phoneme priming effect. The present results show that enhanced phonological processing in middle childhood is restricted to phonemes and does not extend to prosody. These results are indicative of two parallel processing systems for phonemes and prosody that might follow different developmental trajectories in middle childhood as a function of alphabetic literacy.

Tracking independence and merging of prosodic and phonemic processing across infancy

“…The presently observed enhanced negativity to stress overlap in 3‐month‐olds and in 9‐month‐olds is comparable to that obtained for trochaic targets in a previous study with children and adults (Schild et al., ). We can conclude that already 3 months after birth, German infants are able to extract prosodic regularity in the speech stream and use it for phoneme‐free predictive coding of the predominant trochaic stress pattern.…”

“…They seem, rather, to handle both types of information separately from early on. This parallels independent ERP phoneme priming and ERP stress priming in children and adults (Schild et al., ,b). The timing of phoneme priming and prosodic priming in the ERPs is closely related to the temporal characteristics of speech stimuli: Rapidly varying phoneme‐relevant information is earlier available in the speech signal than the more slowly varying prosodic information.…”

“…ERP phoneme priming effects obtained in 6‐month‐olds and 9‐month‐olds are partly consistent with ERP phoneme priming effects previously obtained for infants and young children (Becker et al., ). Previously, we found enhanced frontal negativity paralleled by reduced posterior negativity for phoneme match compared to phoneme mismatch and argued for two different mechanisms: First, we related phoneme priming between 150 and 300 ms following target word onset to a premature form of the adult N100 (Becker et al., ; Duta et al., ; Wunderlich & Cone‐Wesson, ), revealing priming of abstract speech sound representations (Friedrich et al., ; Schild et al., , ; Schild et al., ). Second, we related phoneme priming between 350 and 550 ms (although then with lateralization to right‐hemispheric electrode leads) to the phonological N400 reported in ERP studies with infants, children and adults (Duta et al., ; Mani et al., ; Mills et al., ) indicating predictive phonemic coding on the basis of the primes.…”

“…In addition to separate processing streams, merging of phoneme‐relevant information and prosody was evident when unimodal auditory word onset priming was restricted to the dominant stress pattern in German, that is, to trochaic targets (Schild, Becker, & Friedrich, ). For adults and children (age 5 to 8 years), ERPs mainly reflected independent processing of phonemes and prosody.…”

Phoneme-free prosodic representations are involved in pre-lexical and lexical neurobiological mechanisms underlying spoken word processing

“…While there was enhanced posterior negativity for stress mismatch in the auditory–visual paradigm (Friedrich, Kotz, Friederici, & Alter, 2004; Friedrich, Kotz, Friederici, & Gunter, 2004), there was enhanced posterior negativity for stress match in the unimodal paradigm (Schild et al, 2014). Methodological differences between both studies might exert their influences here.…”