Letter-sound correspondences: New scanning data

A research team in Professor Leo Blomert’s lab at Maastricht University in the Netherlands reported that brain scans of children with and without dyslexia reveal differences when associating letters with sounds. Vera Blau and colleagues studied 34 9-½-year-old children, 18 of whom were identified as having dyslexia. While the children completed tasks under four different conditions (letters presented only visually; speech sounds presented alone; multi-sensory matching letter–sound pairs; and multi-sensory not-matching letter–sound pairs), the researchers obtained scans of brain activity. They found that in the brains of children with dyslexia there were weaker effects when letters and sounds matched than in the brains of children without dyslexia; these effects appeared most clearly in certain areas of the brain related to language function. In addition, the dyslexic readers’ brains showed weaker activation when speech sounds were the only stimulus (i.e., without accompanying letters).

Learning to associate auditory information of speech sounds with visual information of letters is a first and critical step for becoming a skilled reader in alphabetic languages. Nevertheless, it remains largely unknown which brain areas subserve the learning and automation of such associations. Here, we employ functional magnetic resonance imaging to study letter-speech sound integration in children with and without developmental dyslexia. The results demonstrate that dyslexic children show reduced neural integration of letters and speech sounds in the planum temporale/Heschl sulcus and the superior temporal sulcus. While cortical responses to speech sounds in fluent readers were modulated by letter-speech sound congruency with strong suppression effects for incongruent letters, no such modulation was observed in the dyslexic readers. Whole-brain analyses of unisensory visual and auditory group differences additionally revealed reduced unisensory responses to letters in the fusiform gyrus in dyslexic children, as well as reduced activity for processing speech sounds in the anterior superior temporal gyrus, planum temporale/Heschl sulcus and superior temporal sulcus. Importantly, the neural integration of letters and speech sounds in the planum temporale/Heschl sulcus and the neural response to letters in the fusiform gyrus explained almost 40% of the variance in individual reading performance. These findings indicate that an interrelated network of visual, auditory and heteromodal brain areas contributes to the skilled use of letter-speech sound associations necessary for learning to read. By extending similar findings in adults, the data furthermore argue against the notion that reduced neural integration of letters and speech sounds in dyslexia reflect the consequence of a lifetime of reading struggle. Instead, they support the view that letter-speech sound integration is an emergent property of learning to read that develops inadequately in dyslexic readers, presumably as a result of a deviant interactive specialization of neural systems for processing auditory and visual linguistic inputs.

The results presented by Professor Blau are provocative. As they state in the abstract and in the conclusion to their report, “letter-speech sound integration is an emergent property of learning to read.” Why don’t some students develop facility with the integration of the correspondences? Is there something about the practice their receive? Does some small deviation (e.g., being confronted with too many correspondences early in acquiring literacy) deflect the path to competent decoding skill? Do some neural anomalies make aquisition of correspondences more difficult?

Please understand that these results do not validate a type of instruction. The use of “multi-sensory” here is different than it is when used in “multi-sensory instruction.” (Try performing a letter-sound or grapheme-phoneme task without using multiple modalities!).

Blau, V., Reithler, J., van Atteveldt, N., Seitz, J., Gerretsen, P., Goebel, R., & Blomert, L. (2010). Deviant processing of letters and speech sounds as proximate cause of reading failure: a functional magnetic resonance imaging study of dyslexic children. Brain. Epub ahead of print. PMID: 20061325

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