Wednesday, January 26, 2022

Book "The Neural Basis of Reading"

The Neural Basis of Reading
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Best notes:

"Reading is a unique human skill, and modern societies rely extensively on literacy skills. Reading disability can therefore have a profound personal, economic, and social impact"

"Visual word recognition is an important (and probably the best understood) component of reading."

"The process of silent word reading minimally requires two types of codes: orthographic (knowledge about letter identities and letter position) and semantic (knowledge about the meanings of words)."

"Sensitivity to the features of letters and the position of letters within words is vital to reading. It exlpians the ablity to "raed txet sUcH aS tHiS", it explains why we can navigate through a page of text which is otherwise simply a highly cluttered visual scene"

"when reading, the eyes are moving fast—very, very fast—and during these fast jumps across the word or line, the visual system is processing lines, corners and edges, constructing letters, concatenating information to information already processed, and calculating what to process next. This information is integrated with higher cortical mechanisms (for example, memory, language, attention) because reading is also an example of cognitive pattern recognition. It is these more cognitive mechanisms that are generally the focus in models of reading; however, it is nevertheless undeniable that the front-end of this highly interactive system is spatio-temporal visual processing."

"The fact that word recognition is limited by letter recognition does not obviate subsequent parallel and cascaded processing, such that after the initial selection and assembly of the visual pattern of a word, the activation of letters and subsequent word recognition can proceed by any parallel and cascaded process, as advocated in any number of models of word recognition (e.g., Seidenberg & McClelland, 1989; Plaut, McClelland, Seidenberg, & Patterson, 1996)."

"a dependence on the accurate encoding of individual letters is not the same thing as letter-by-letter reading, which is generally believed to be a serial process."

"dyslexia is entirely the result of poor phonological representations"

"SERIOL Model. It is well known that neural representations increase in abstractness as distance from the periphery increases. The SERIOL model offers a comprehensive theory of the representational transformations carried out by a skilled reader in the processing stream extending from primary visual cortex to lexical access (along the orthographic, lexical route)."

"The SERIOL framework is comprised of five layers: edge, feature, letter, bigram, and word. Each layer is comprised of nodes, corresponding to neural assemblies. For the edge, feature, and letter layers, a letter’s activation is taken to be the total amount of neural activity devoted to representing that letter. Thus, a letter’s activation increases with number the of nodes activated by the letter, and their firing rate and firing duration."

"Brain-imaging indicates a single lexical route to the lexicon (Cohen et al., 2000; Dehaene et al., 2004; Tarkiainen, et al. 1999), as would be expected on the basis of parsimony. That is, it would be inefficient to have separate modes of lexical processing for the LVF and RVF, and it is unclear how separate modes could be integrated together for a string crossing both VFs. Moreover, theoretical and experimental investigations based on the SERIOL model show that VF asymmetries can and do arise from orthographic activation patterns (Whitney, 2004; Whitney & Lavidor, 2004; Whitney & Lavidor, 2005). Therefore, it should be assumed that asymmetries in half-field studies reflect differences originating in prelexical, visual processing."

"Reading is one of the most important human cognitive skills. It is also one of the most artificial and complex, depending as it does on the automatic and accurate integration of visual word forms (orthography), auditory word sounds (phonology), and conceptual word meanings (semantics)"

"Visual features are extracted from the printed image and combined to form individual letters. These individual letters and letter clusters are converted into whole words to which meaning must then be applied via successful lexical access. Once the semantic information stored in the lexicon has been retrieved, the meaning of individual words is combined within the context of the sentence to produce a coherent meaning."

"mapping of 1,120 graphemes onto the 40 phonemes that constitute the English"

"brain regions are differentially involved in early reading and in skilled reading leads us to question the extent to which patterns of brain activation seen in good readers are reflected in the functional activations of children and adults with developmental dyslexia."

"There may be columns of neurons specialized for the recognition of letters, graphemes, or words, but they are likely to be intermixed with other neurons involved in object and face recognition (Allison, Puce, Spencer, & McCarthy, 1999). Therefore, at the scale accessible to human neuroimaging, most if not all of the cortical surface is likely to respond jointly to words, faces, and objects with smooth but systematic changes in local selectivity (Haxby et al., 2001)."

"reading acquisition proceeds by selection and local adaptation of a preexisting neural region, rather than by de novo imposition of novel properties onto that region."

"Only a single simulation model (Mozer, 1987) included a hierarchical processing stream capable of extracting a location-invariant code from a simulated retinal input (although no solution was proposed for case-invariance)."

"we have proposed a tentative neurobiological scheme called the local combination detectors (LCD) model (Dehaene et al., 2005)"

"The local combination detector scheme can thus explain why open bigrams are used in reading, rather than merely stipulating their existence. Furthermore, most of the desirable properties of the open-bigram scheme are preserved. In particular, strings with missing letters, such as “GRDN,” activate neurons that form a subset of the code for the full word “GARDEN,” thus explaining that one can prime the other (Humphreys et al., 1990; Peressotti & Grainger, 1999)."

"After the bigram level, the natural next step is ordered combinations of bigrams. Here, we expect neurons to begin to react to recurring multiletter strings, including morphemes or small words (Fig. 5.1). Note, however, that at any stage, words are never encoded by a single neuron or column, but by a sparsely distributed population of partially redundant neurons."

"Although letters and bigrams are the relevant units in alphabetic scripts, the same model should ultimately be able to simulate the acquisition of reading in any script."

"By presenting strings of symbols containing a hierarchy of stimuli designed to progressively stimulate increasingly higher levels of the proposed cortical hierarchy (falsefont stimuli, infrequent letters, frequent letters, frequent bigrams, frequent quadrigrams, and real words), we recently demonstrated a systematic progression of activation from posterior occipital to anterior fusiform, as predicted by the LCD model (Vinckier et al., 2007). Bigram frequency has also been found to modulate the VWFA activation (Binder et al., 2006)."

"At its core, reading is fundamentally about converting graphic input to linguistic-conceptual objects (words and morphemes). A universal theory of reading must explain how this occurs, considering the form of the graphic input and how it maps to phonological and semantic representations."

"The alphabetic reading network includes posterior visual regions (occipital areas and the left mid-fusiform gyrus) for orthographic processes, temporal/ parietal and anterior areas (superior temporal sulcus and inferior frontal sulcus/insula) for phonology, and both posterior (anterior fusiform) and anterior regions (inferior frontal gyrus) for meaning."

"Some uncertainty remains about the role of temporal and parietal areas that support word-level phonology. The left superior temporal gyrus is important in alphabetic reading"

"Reading in alphabetic languages consistently activates the inferior frontal gyrus. The activity in this region is closely associated with activity in the temporal-parietal area and is thus also generally thought to be involved in the recoding of visual information into phonological information (Sandak et al., 2004)."

"On the basis of this focused review, it is clear that MEG can reveal not only the sequence of cortical activations underlying visual word recognition, but also the dynamic interplay between the nodes of the cortical network. It is also clear that MEG data show both similarities and differences when compared to fMRI. This poses a challenge for integrating information from both modalities. Crucially, these recent results from MEG and EEG/ERP strongly suggest that visual word recognition involves very early interactions between the vision and language domains in skilled adult readers."

"The efficiency of the visual system of literate adults during reading reflects its ability to identify rapidly and in parallel arrays of several letters. Indeed, reading latencies are fairly constant irrespective of word length, at least within a range of about three to six letters (Lavidor & Ellis, 2002; Weekes, 1997) (Fig. 9.1). This perceptual ability takes about 5 years of instruction to develop, and an effect of word length persists at least to the age of 10 (Aghababian & Nazir, 2000). In addition to the processing of foveal strings of letters, text reading also requires the ability to explore sequentially arrays of words, on the basis of parafoveal vision, attentional scanning, and oculomotor control (Sereno & Rayner, 2003)."

"In summary, there are indications that the left posterior visual system is crucial for important features of expert reading, namely the fast and parallel computation of abstract letter identities."

"the most dramatic letter-by-letter reading effects occur in patients with lesions to the left-hemispheric ventral pathway. As a final point, the efficacy of the various processing stages may differ across subjects in proportion to their reading expertise, a source of variability that should be kept in mind when interpreting the performance of individual patients."

"In agreement with the dissection of the cerebral visual system into early visual cortex, ventral stream, and dorsal stream, we will now sketch in turn the features of hemianopic, ventral, and dorsal dyslexias."

"Letter-by-letter reading is the most frequent but certainly not the more dramatic form of pure alexia."

"Conclusion. Functional neuroimaging studies of reading have been invaluable for identifying the networks of brain regions engaged in various aspects of reading. Evidence that acute dysfunction (damage or hypoperfusion) in each of these brain regions reliably disrupts some aspect of reading can confirm that each of these areas is essential for a particular component process underlying reading. Studies of acute functional lesions (using DWI and PWI) and reading complement the functional imaging studies, by testing hypotheses generated from functional imaging studies concerning the role of particular areas (right and left inferior parietal lobule, right and left mid-fusiform gyrus, and Broca’s area) in reading."

"Phonological assembly refers to the operations associated with mapping from the orthographic to the phonological form in printed word identification. The failure to develop efficient phonological assembly skills in word and pseudoword reading, in turn, appears to stem from difficulties—at the earliest stages of literacy training—in attaining fine-grained phonemic awareness. Phonological awareness in general is defined as the metalinguistic understanding that spoken words can be decomposed into phonological primitives, which in turn can be represented by alphabetic characters (Brady & Shankweiler, 1991; Bruck, 1992; Fletcher et al., 1994; Liberman et al., 1974; Rieben & Perfetti, 1991; Shankweiler et al., 1995; Stanovich & Siegel, 1994)."

"the first requirement for skilled reading is rapid visual analysis of the letters and their order."

"Conclusion. The most important theme of this chapter is that the ability to read depends greatly on the temporal processing systems of the brain: the visual magnocellular system for sequencing letters and words accurately and gating their access to the visual ventral stream for their identification; its auditory equivalent, which responds to the frequency and amplitude transients that distinguish letter sounds; together with motor timing systems, particularly those supplying and mediated by the cerebellum, which coordinate reading eye movements, speaking, and writing. These supply the reading network, which overlays similar processing modules used for speech and language comprehension.Four main linked components of the reading network exist in the LH. The first is the VWFA situated in the left anterior fusiform gyrus, where letters are identified by the ventral visual stream. The second consists of Wernicke’s area communicating with the supramarginal and angular gyri at the left temporoparietal junction. Here, auditory and visual representations are integrated with the meaning of words stored in the semantic lexicon. These project via the arcuate fasciculus to the third main component, which is located in the left IFG, including Broca’s area. These areas are activated even for silent reading as well as reading out loud. The fourth important component is the right cerebellar hemisphere, which coordinates the other three."

"Fusiform Visual Word Form Area. The only completely new region that seems to have developed specifically for reading is an area known as the VWFA, which is situated in the anterior part of the left fusiform gyrus on the undersurface of the occipital lobe and extends forward into the back of the middle temporal gyrus (Cohen, Henry et al. 2004))"

"the child learns the visual form of several words, so that he no longer has to translate them into their auditory forms, but can immediately recognize the word visually and retrieve its meaning. A little later, he can extract meaning, not word by word, but from a whole group of words in a phrase or even in a whole sentence."

"During each fixation this “attentional spotlight” probably not only feeds letters, one after the other through for identification by the ventral stream, but it also defines their spatial location with respect to each other. Thus, during each fixation of about 250 ms, seven or eight letters are accessed sequentially without moving the eyes (Vidyasagar, 2004). Consistent with this, serial visual search has been found to be critically dependent upon activation of magnocellular pathways (Cheng, Eysel et al. 2004)"

"numerous studies have now shown that poor readers are significantly slower at serial visual search (Iles, Walsh et al. 2000) and greatly affected by distractors (Facoetti, A et al. 2001)."

"the main reason why it takes such a long time for children to learn to read fluently may be because training the visual attentional search mechanism to work properly for reading is a slow process."

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