Poster B20, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
Neural and perceptual phoneme discrimination in an acoustically variable context is compromised in dyslexia
Paula Virtala1, Sanna Talola1, Eino Partanen1, Teija Kujala1;1Cognitive Brain Research Unit, University of Helsinki
Natural speech includes acoustic variation between and within speakers. Still, healthy adults and even newborns process and categorise speech sounds effortlessly. The case may be different in individuals suffering from the reading deficit developmental dyslexia, known to degrade auditory and phonological processing. The present study investigated neural and perceptual processing of phonemes embedded in an acoustically variable or constant context in developmental dyslexia. Dyslexic (n=18) and typically reading (n=20) adults heard acoustically distinctive /æ/ and /i/ phonemes belonging to their native language Finnish. Their electroencephalogram (EEG) was recorded to study the change-related mismatch negativity (MMN) and P3a responses to the phoneme changes. Response amplitudes were compared between groups, constant and variable auditory contexts, and ignore and attentive listening conditions. The participants also reacted to phoneme changes by button presses in a separate condition, in order to compare the groups in perceptual discrimination accuracy (hit-ratio) and speed (reaction time). The MMN amplitude was diminished in dyslexic participants in variable but not constant auditory context. Also the hit ratio was smaller in dyslexics than typical readers in the variable context. According to our results, even very distinctive native language phonemes are challenging to discriminate for dyslexics when the context resembles natural variability of speech. This poor tolerance to acoustic variation in speech could underlie dyslexics’ difficulties in forming strong neural representations of native language phoneme categories during development. Furthermore, future studies should take into account that simple, repetitive stimuli may be insensitive to the speech processing deficits in dyslexia.
Themes: Disorders: Developmental, Speech Perception
Method: Electrophysiology (MEG/EEG/ECOG)