Reading from a neurolinguistic perspective

1. Bastiaan de Boer Reading from a neurolinguistic perspective Deep dyslexia Several models have been proposed to explain deep dyslexia reading performance. Now follows a review of these models with an emphasis on the manner in which these frameworks conceptualize both the occurrence of semantic errors and the inability to read aloud nonwords. 1) The dual route account: Morton and Patterson-model Deep dyslexia reflects multiple sites of damage within the dual-route model for reading. The inability to read aloud nonwords is caused by the unavailability of the route, through which people assemble phonology. Instead, reading is assumed to proceed through the semantically mediated adressed route, which is normally capable of supporting reading through whole word access, but because of semantic errors, this route is also assumed to be damaged. 2) The continuum account: phonological and deep dyslexia Deep and phonological dyslexia represent the endpoint along the same continuum of reading disability. This is based on reports of patients that initially got the diagnosis of deep dyslexia, but over time evolved to a pattern of impairment associated with phonological dyslexia. Glosser and Friedman, in contrast to Moron and Patterson, argue for a model in which reading via the nonsemantic route is accomplished by locating subword orthographical information directly to phonological entries in the output lexicon. According to this account, the evolution from deep to phonological dyslexia reflects the recovery of the semantic system and thus the disappearance of semantic errors. 3) The connectionist account A computational model of normal reading is implemented as nodes interconnected to a parallel distributed processing network. The nodes form layers that represent various features of a word. Plaut and Shallice produced many deficits analoguous to those in deep dyslexia by introducing a single lesion to a connectionist network that located ortography to phonology via semantics. However, they used connectionist networks that mapped semantic activation directly onto the phonological layer. Given that nonwords have no semantic representation, these networks could not support nonword reading. 4) The right hemisphere hypothesis: the neurological account According to the right hemisphere hypothesis, deficits in deep dyslexia reflect the contributions of the right hemisphere to reading after the dominant left hemisphere has been damaged. The damage to the left hemisphere eliminates acces to the left orthographic lexicon. To continue the process of reading acces to the right hemisphere is necessary, although this hemisphere can't subserve the production of language. Therefore, once the orthographic lexicon accesses the semantic representation, it is transmitted from the right to the left hemisphere, after which the assembled information is used to access a phonological entry in the left hemisphere, where a pronounciation is selected and produced. 5) The Failure of Inhibition Theory (FIT) Each of the aforementioned models of deep dyslexia assume multiple locations of damage in the reading system. In contrast, Buchanan a.o. proposed in FIT that selection impairment, due to failure of inhibition in the phonological output lexicon, alone accounted for the various types of reading errors in deep dyslexia. According to FIT, lexical access in deep dyslexia can be achieved via either the addressed route for real words or the assembled routine for unfamiliar words and nonwords.1 1=Colangelo, A., Buchanan, L., Localizing damage in the functional architecture: The distinction between implicit and explicit processing in deep dyslexia, Journal of Neurolinguistics 20 (2007) 114-116.

2. Irony and metaphor comprehension Apart from how specific fysical disorders, like deep dyslexia, influence reading, one can also investigate how reading ’influences' the brain, i.e. how different genres like metaphor and irony are processed. In the last decades, studies of the functional architecture of linguistic abilities in the brain have examined the relative abilities of the two cerebral hemispheres, and have revealed that although the left hemisphere (LH) is dominant for the majority of language functions, the right hemisphere (RH) is involved in the processes of narrative construction and discourse representation. The involvement of the RH in the processing of verbal irony, conventional and novel metaphors have been examined by Eviatar and Just. Higher levels of discourse processing evoke patterns of cognition and brain activation that extend beyond the literal comprehension of sentences. Eviatar and Just used fMRI to examine brain activation patterns while 16 healthy participants read brief three-sentence stories that concluded with either a literal, metaphoric, or ironic sentence. The fMRI images acquired during the reading of the critical sentence revealed a selective response of the brain to the two types of nonliteral utterances. Metaphors Metaphoric utterances resulted in significantly higher levels of activation in the left inferior frontal gyrus and in bilateral inferior temporal cortex than the literal and ironic utterances. Irony Ironic statements resulted in significantly higher activation levels than literal statements in the right superior and middle temporal gyri, with metaphoric statements resulting in intermediate levels in these regions. 2 2 = Eviatar, Z., Just, M.A., Brain correlates of discourse processing: An fMRI investigation of irony and conventional metaphor comprehension, Neuropsychologia 44 (2006) 2348–2359.

3. Processing complex writing systems: Japanese Cerebral mechanisms of language are subject to continuing investigation. With the emergence of functional brain imaging techniques, the study of language-specific mechanisms in the brain of neurologically intact subjects has become possible. The most recent of these techniques is Magnetoencephalography (MEG), that affords mapping of task-specific changes in neurophysiological activity in real time. • Previous MEG studies on monolingual and English–Spanish bilingual speakers show strong predominance of activity in left hemisphere areas, manifested after the initial sensory (visual) processing of the printed stimuli. These studies conducted with Spanish and English speaking participants, predominantly showed activation of: • the ventral occipitotemporal areas (graphemic/orthographic processing) • the posterior part of the superior temporal gyrus (phonological decoding) • the middle temporal gyrus / mesial temporal cortex (lexical/semantic processing) • the inferior frontal region (articulatory recoding) • the angular gyrus (word recognition) Quantitative and qualitative hemispheric asymmetry studies executed by Valaki a.o. on Japanese native speakers show left-hemisphere superiority for phonetic processing. Studies on Japanese patients with pure alexia imply that the semantic processing of reading Kanji (a logographic script borrowed from Chinese) words depends on the left posterior inferior temporal area, while the phonological reading of Kana (a phonetic syllabary script used for rendering foreign names and loan-words) is mediated by the left angular gyrus. The literature suggests that at least partially overlapping brain circuits are involved in processing the three components of the Japanese writing system: Kanji, Hiragana (a phonetic syllabary script used for general purpose transcription) and Kana. The MEG study addressed the question as to whether the Japanese mixed logographic and syllabary writing system involves different patterns of brain activation for language comprehension, as opposed to the established patterns in Indo-European languages with alphabetical writing systems. The activation of the temporoparietal areas, and the middle/mesial and the inferior frontal activity suggest similarities with profiles established in previous reading comprehension studies involving (indo-european) alphabetic writing systems.3 3 = Valaki, C., Do different writing systems involve distinct profiles of brain activation? A magnetoencephalography study, Journal of Neurolinguistics 16 (2003) 429–438.