Speech perception deficits in developmental dyslexia were investigated in quiet and various noise conditions. Dyslexics exhibited clear speech perception deficits in noise but not in silence. Place-of-articulation was more affected than voicing or manner-of-articulation. Speech-perception-in-noise deficits persisted when performance of dyslexics was compared to that of much younger children matched on reading age, underscoring the fundamental nature of speech-perception-in-noise deficits. The deficits were not due to poor spectral or temporal resolution because dyslexics exhibited normal 'masking release' effects (i.e. better performance in fluctuating than in stationary noise). Moreover, speech-perception-in-noise predicted significant unique variance in reading even after controlling for low-level auditory, attentional, speech output, short-term memory and phonological awareness processes. Finally, the presence of external noise did not seem to be a necessary condition for speech perception deficits to occur because similar deficits were obtained when speech was degraded by eliminating temporal fine-structure cues without using external noise. In conclusion, the core deficit of dyslexics seems to be a lack of speech robustness in the presence of external or internal noise.

Although the causes of dyslexia are still debated, all researchers agree that the main challenge is to find ways that allow a child with dyslexia to read more words in less time, because reading more is undisputedly the most efficient intervention for dyslexia. Sophisticated training programs exist, but they typically target the component skills of reading, such as phonological awareness. After the component skills have improved, the main challenge remains (that is, reading deficits must be treated by reading more—a vicious circle for a dyslexic child). Here, we show that a simple manipulation of letter spacing substantially improved text reading performance on the fly (without any training) in a large, unselected sample of Italian and French dyslexic children. Extra-large letter spacing helps reading, because dyslexics are abnormally affected by crowding, a perceptual phenomenon with detrimental effects on letter recognition that is modulated by the spacing between letters. Extra-large letter spacing may help to break the vicious circle by rendering the reading material more easily accessible.

Visual-attentional theories of dyslexia predict deficits for dyslexic children not only for the perception of letter strings but also for non-alphanumeric symbol strings. This prediction was tested in a two-alternative forced-choice paradigm with letters, digits, and symbols. Children with dyslexia showed significant deficits for letter and digit strings but not for symbol strings. This finding is difficult to explain for visual-attentional theories of dyslexia which postulate identical deficits for letters, digits and symbols. Moreover, dyslexics showed normal W-shaped serial position functions for letter and digit strings, which suggests that their deficit is not due to an abnormally small attentional window. Finally, the size of the deficit was identical for letters and digits, which suggests that poor letter perception is not just a consequence of the lack of reading. Together then, our results show that symbols that map onto phonological codes are impaired (i.e. letters and digits), whereas symbols that do not map onto phonological codes are not impaired. This dissociation suggests that impaired symbol-sound mapping rather than impaired visual-attentional processing is the key to understanding dyslexia.

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Specific language impairment (SLI) is one of the most common childhood disorders, affecting 7% of children. These children experience difficulties in understanding and producing spoken language despite normal intelligence, normal hearing, and normal opportunities to learn language. The causes of SLI are still hotly debated, ranging from nonlinguistic deficits in auditory perception to high-level deficits in grammar. Here, we show that children with SLI have poorer-than-normal consonant identification when measured in ecologically valid conditions of stationary or fluctuating masking noise. The deficits persisted even in comparison with a younger group of normally developing children who were matched for language skills. This finding points to a fundamental deficit. Information transmission of all phonetic features (voicing, place, and manner) was impaired, although the deficits were strongest for voicing (e.g., difference between͞b͞and͞p͞). Children with SLI experienced perfectly normal ''release from masking'' (better identification in fluctuating than in stationary noise), which indicates a central deficit in feature extraction rather than deficits in low-level, temporal, and spectral auditory capacities. We further showed that speech identification in noise predicted language impairment to a great extent within the group of children with SLI and across all participants. Previous research might have underestimated this important link, possibly because speech perception has typically been investigated in optimal listening conditions using non-speech material. The present study suggests that children with SLI learn language deviantly because they inefficiently extract and manipulate speech features, in particular, voicing. This result offers new directions for the fast diagnosis and remediation of SLI.phonetic deficit ͉ auditory deficit ͉ speech intelligibility ͉ masking noise ͉ specific language impairment M any children experience unexpected difficulties in understanding and producing spoken language despite normal intelligence, normal hearing, normal opportunities to learn language, and in the absence of any obvious neurological problems (for review, see ref. 1). This disorder is typically called specific language impairment (SLI). In the past years, research on SLI has experienced a growth of interest partially because it has become clear that more children than initially thought show language learning difficulties. Indeed, recent epidemiological studies estimate the incidence of SLI to be Ϸ7.4% in a population of monolingual English-speaking kindergarten children (2). Children with SLI exhibit deficits in several aspects of language, including phonology, morphology, and syntax (1, 3). One of the hallmarks of SLI is a deficit in the use of function morphemes (e.g., the, a, and is) and other grammatical morphology (e.g., plural -s, past tense -ed). Children with SLI also are at high risk for subsequent literacy problems (4).The causes of SLI are still hotly debated. Current theories of SLI fall into two categ...