Transcript Dia 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
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.
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