Читать книгу The Science of Reading - Группа авторов - Страница 22

Disruptions to the development and operation of visual word identification arise from inadequate orthographic‐phonological knowledge sources and/or the processes that use these knowledge sources, as shown in Figure 1.2. Because visual input initiates word identification, hypotheses about its disruption (in visual processes) emerged in the earliest observations of acquired dyslexia (Pringle‐Morgan, 1896; see Woollams et al., this volume), then developmental dyslexia (Orton, 1925; see Wagner et al., this volume) and in later work inspired by visual neuroscience (Lovegrove et al. 1986; Facoetti et al, 2019). However, it is now well established that the primary causes of disruption lie in the orthographic‐phonological phases of identification.

Figure 1.2 The word‐identification system of the Reading Systems Framework. “Phonological units” rather than “language units” are highlighted to reflect their specific importance in dyslexia.

The link between skilled and disrupted word identification processes is made explicit in dual‐route models, which postulate selective disruption to either the direct (lexical) route or the indirect (sublexical) route to word identity. Castles and Coltheart (1993) established the existence of each type of disruption by testing children’s performance on both irregular, exception words (requiring the lexical route) and pseudowords (requiring the sublexical route). Although a problem with both kinds of words was most common, disassociations between exception word and pseudoword performance appeared for some children. Most showed a phonological dyslexia profile (more difficulty with pseudowords), while others showed a surface dyslexia pattern (more difficulty with exception words). In the Reading Systems Framework, the surface dyslexic is impaired in visual‐orthographic memory, whereas the phonological dyslexic is impaired in the linkage between sublexical orthographic strings and pronunciations.

These two different manifestations of disruption to the word reading system might, however, arise from a single problem in the phonological system. Difficulty reading exception words might be recast not as surface dyslexia but as due to a developmental delay (Manis et al., 1996) – that is, reading experience that is insufficient to acquire high‐quality word representations of exceptionally spelled words. A connectionist model by Seidenberg and McClelland (1989) showed the plausibility of a key assumption: A serious problem in phonological representations can lead to a “deficit” in reading exception words. Other studies – a review by Rack et al. (1992), a critique of visual deficit hypotheses (Vellutino, 1981), demonstrations of phonological processing and memory deficits (Brady & Shankweiler, 1991; Snowling et al., 1986) and a review of acquired dyslexia cases (Ramus, 2003) – added to the persuasiveness of the phonological deficit hypothesis. Imaging results converged to show associations between reading problems and failures to engage left hemisphere language areas (Shaywitz et al., 2004; Simos et al., 2007; Turkeltaub et al., 2003). Although the cause of phonological problems is uncertain, there is evidence that they originate prior to literacy: Among children at risk for dyslexia, preliterate language skills predict their phonological skills and subsequent reading skills (Hulme et al., 2015; Snowling et al., 2003). Moreover, interventions can improve children’s oral language skills and their prospects for reading (Hulme et al., 2020).

Other work has suggested that phonological problems may reflect lower level deficits in, for example, temporal coding in the auditory system (Tallal, 1980) or the perception of speech (Noordenbos & Serniclaes, 2015; although others have questioned these ideas (e.g., Strong et al., 2011; Snowling et al., 2019). Further, it has been proposed that automatized naming problems (e.g., & Wolf, 2011), when added to a phonological deficit, produce a “double deficit” (Wolf & Bowers, 1999) and Ziegler et al. (2019) concluded that most children show phonological deficits while also showing weaknesses in nonphonological tasks, especially letter detection. Although there are potentially multiple causes of disruption to the word‐identification system, the phonological deficit hypothesis is supported by extensive evidence and is now the standard theory. Indeed, a phonological deficit is part of the definition of dyslexia provided by the International Dyslexia Association (https://dyslexiaida.org/definition‐of‐dyslexia/).