A phonological deficit or a broader auditory deficit as a core impairment of dyslexia?

Ahissar, M. 1 & Ghesquière, P. 2

1 Department of Psychology, Faculty of Social Sciences - The Hebrew University of Jerusalem. Israel
2 Humanities and Social Sciences at Katholieke Universiteit Leuven, Belgium

Auditory working memory as an underlying deficit in Dyslexia, Merav Ahissar.

A typical characteristic of Dyslexic individuals is their poor working memory. Though mainly studied in the verbal domain (e.g. Digit span), auditory working memory was found to be systematically impaired in Dyslexia across stimulus types. We previously suggested the ?anchoring deficit? which proposes that implicit aspects of working memory, which track regularities in incoming auditory stimuli, are impaired in Dyslexia (Ahissar et al., Nat Neurosci, 2006; Ahissar, TICS, 2007). This hypothesis explains Dyslexics? difficulties in acquiring efficient reading as stemming from difficulties in detecting the repeated underlying phonological patterns that characterize their language. Consequently, they need to actually ?read?, i.e. map the orthography to phonology, rather than retrieve only few reliable cues, as expert readers do. This hypothesis further explains Dyslexics? additional difficulties, e.g. poor performance in auditory discrimination tasks, as revealing a failure to utilize regularities in the sequence of auditory stimuli which typically facilitates perceptual performance (Oganian & Ahissar, 2012). We recently developed a computational model that dissociates between sensory noise and the contribution of recent history (working memory) in discrimination tasks (Raviv, Ahissar & Loewenstein, 2012). We indeed found that Dyslexics differ in their reduced weighting of recent history rather than in their increased sensory noise. The existence of Dyslexic musicians seems to challenge this auditory-general view, since musicians are known as very sensitive to sounds, and as having enhanced auditory working memory. We tested this population and found that even Dyslexic musicians have difficulties in non-verbal auditory memory (e.g. memory for pitch and for rhythm) compared with their peers. Moreover, their non-verbal auditory working memory is mainly impaired in its chunking ability, suggesting reduced ability to utilize regularities. Their working memory was a reliable predictor of their reading accuracy, as previously found for other dyslexic populations.

Temporal auditory processing and speech perception as possible underlying deficits of the phonological problems in persons with dyslexia, Pol Ghesquière.

Mapping graphemes to phonemes (the essence of reading) builds upon phonological awareness of the child, i.e. the consciousness of the sound structure of spoken language and the skill to manipulate it. Preschool children manipulate speech mainly at the syllable level. Only during reading acquisition phoneme awareness emerges and explicit phoneme representations develop. However, in order to develop clear phonological representations at syllable and phoneme level, the auditory system must be able to accurately process dynamic acoustic cues that are crucial for speech perception. Because of the importance of auditory sensitivity in reading acquisition, auditory processing and speech perception skills have received increasing attention in relation to dyslexia. Yet, only little evidence exists on the causal influence of these skills on reading development and on their specific nature. Therefore in 2003, we started a longitudinal project starting before the formal instruction of reading until the end of primary school. This project demonstrated that children with dyslexia have pre-reading deficits in auditory processing, speech perception and phonology, but more importantly, that basal auditory temporal processing and speech perception in kindergarten uniquely contribute to growth in reading ability. This is the first study that demonstrates that auditory processing and speech perception impairments in dyslexia are not merely an epiphenomenon of reading failure but that they precede and possibly contribute to the reading development. In a second cross-sectional project, involving 12-year-olds and adults diagnosed with dyslexia, we further investigated the precise nature of their auditory and speech perception problems. More specifically, by applying a balanced design we investigated whether the deficit is specific to speech and/or specific to temporal processing. Results show that both 12-year-olds and adults with dyslexia have an auditory temporal processing deficit which is not speech-specific.