Context-Dependent Encoding in the Human Auditory Brainstem Relates to Hearing Speech in Noise: Implications for Developmental Dyslexia

SummaryWe examined context-dependent encoding of speech in children with and without developmental dyslexia by measuring auditory brainstem responses to a speech syllable presented in a repetitive or variable context. Typically developing children showed enhanced brainstem representation of features related to voice pitch in the repetitive context, relative to the variable context. In contrast, children with developmental dyslexia exhibited impairment in their ability to modify representation in predictable contexts. From a functional perspective, we found that the extent of context-dependent encoding in the auditory brainstem correlated positively with behavioral indices of speech perception in noise. The ability to sharpen representation of repeating elements is crucial to speech perception in noise, since it allows superior “tagging” of voice pitch, an important cue for segregating sound streams in background noise. The disruption of this mechanism contributes to a critical deficit in noise-exclusion, a hallmark symptom in developmental dyslexia

Aggregate neural responses to speech sounds in the central

auditory syste

Brainstem responses to speech syllables

OBJECTIVE: To establish reliable procedures and normative values to quantify brainstem encoding of speech sounds. METHODS: Auditory brainstem responses to speech syllables presented in quiet and in background noise were obtained from 38 normal children. Brainstem responses consist of transient and sustained, periodic components—much like the speech signal itself. Transient peak responses were analyzed with measures of latency, amplitude, area, and slope. Magnitude of sustained, periodic frequency-following responses was assessed with root mean square, fundamental frequency, and first formant amplitudes; timing was assessed by stimulus-to-response and quiet-to-noise inter-response correlations. RESULTS: Measures of transient and sustained components of the brainstem response to speech syllables were reliably obtained with high test–retest stability and low variability across subjects. All components of the brainstem response were robust in quiet. Background noise disrupted the transient responses whereas the sustained response was more resistant to the deleterious effects of noise. CONCLUSIONS: The speech-evoked brainstem response faithfully reflects many acoustic properties of the speech signal. Procedures to quantitatively describe it have been developed. SIGNIFICANCE: Accurate and precise manifestation of stimulus timing at the auditory brainstem is a hallmark of the normal perceptual system. The brainstem response to speech sounds provides a mechanism for understanding the neural bases of normal and deficient attention-independent auditory function

Seeing speech affects acoustic information processing in the human brainstem.

Afferent auditory processing in the human brainstem is generally assumed to be determined by acoustic stimulus features and immune to stimulation by other senses or cognitive factors. In contrast, we show that lipreading during speech perception influences acoustic processing astonishingly early. Event-related brainstem potentials were recorded from 10 healthy adults to concordant (acoustic-visual match), conflicting (acoustic-visual mismatch) and unimodal stimuli. Audiovisual interactions occurred around 11ms post-stimulation and persisted for the first 30ms of the response. Furthermore, response timing and magnitude depended on audiovisual pairings. These findings indicate that early auditory processing is more plastic than previously thought