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• this lecture will examine how written language is processed as revealed by neuropsychological findings

• how do people normally read (mostly single words), what occurs when that system is damaged?

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• History• reading impairment resulting from acquired brain damage is

called an acquired dyslexia– Dejerine (1892) distinguished two types of acquired

dyslexiaalexia with agraphia (an impairment of reading and writing

(spelling)alexia without agraphia (an impairment of reading without a

writing impairment) e.g., Howard Engel, a Canadian mystery writer; Benny

Cooperman is the name of his detective

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• Model of syndrome (Dejerine)– centre existed for the processing of visual images of

letters that mediated reading and writing– located in the angular gyrus region of the left parietal

lobe– when this region was damaged it would impair

reading and spelling– when only reading damaged, it was hypothesized that

visual areas feeding into this centre were damaged

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• Field of acquired dyslexia changed dramatically with Marshall & Newcombe (1973) publication– this paper investigated the pattern of errors made

by dyslexic patients

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– showed that there were two types of patientsone type of patient made grapheme to phoneme errors (e.g.,

insect ->insist, hard to soft c; incense ->increase, soft to hard c)grapheme-unit of written language, roughly a letterPhoneme- unit of spoken language, roughly sound of a letterdescribed patients making this type of error surface dyslexicsother type of patient made semantic substitution errors (e.g.,

speak -->talk, sick -- > ill, mud -- > quagmiredescribed these patients as deep dyslexicsDescribe Tom

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– Proposed two-route model of readingaccording to this model a written word when read can

access its memory representation via two routes -- either directly through its orthographic (visual word form) representation or indirectly through its phonological representation (recall, Posner)

surface dyslexia results when semantic route is damaged

deep dyslexia occurs when phonological route is damaged

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– Types of dyslexia: there appear to be 2 different types of dyslexia: peripheral dyslexias, impairments that interfere with the processing of a word as a word form, and central dyslexias, impairments that occur afterward

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• Peripheral dyslexias– Letter-by-letter reading

Letter-by-letter reading also called alexia without agraphia, agnosic alexia, word-form dyslexia

patients with this disorder read letters much better than words, and appear to read by building up word one letter at a time in a slow, laboured process – describe GM

quantitative data support this hypothesis

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• As Table 4.1 shows– Letter-by-letter readers show a word length effect that is

almost linear– in addition, letter reading errors appear to be correlated

with the time to read words– further results show that letter-by-letter readers find it

much more difficult to read words that are written in script

– also, accuracy performance decreases if exposure duration is reduced

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• Results suggest patients with alexia have to use an explicit letter-by-letter process in order to read a word– theoretical question: is letter-by-letter reading a

consequence of a perceptual deficit that is limited to the processing of written stimuli or is it a more general deficitif the deficit is specific this would suggest that there are

perceptual modules that are specific to the reading process (this issue is unresolved currently)

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– Evidence appears to favour the hypothesis that letter-by-letter reading is a consequence of a specific impairment

– letter-by-letter reading however, appears to be a compensatory strategy, rather than a feature of normal reading. Therefore, understanding letter-by-letter reading may provide little insight into the cognitive processes underlying normal reading

– put another way, letter-by-letter reading does not reflect a reduced set of normally operating processes

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– What is impaired in letter-by-letter readers?Standard hypothesis is that there is a deficit in the

processing of orthographic information?To test whether the alternative hypothesis that the

deficit might be in the naming of the word, Patterson & Kay (1982) showed words briefly (for 2 sec) and then had letter-by-letter readers make categorical judgements. Results showed that subjects were unable to make categorical judgements for words that could not be read immediately

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– Two similar models of letter-by-letter reading have been proposed by Patterson and Kay and by Warrington and Shallice

– note: in both models compensatory processes are hypothesized

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• Surface dyslexia– surface dyslexics appear to have difficulty mapping

graphemes into phonemes (letter combinations into sounds)– characterizing the grapheme to phoneme failures

assigning inappropriate sound when grapheme is ambiguous or depends on context (e.g., insect ->insist (hard to soft c); guest -> just (hard to soft g)

assigning a phonetic value to a soft grapheme (e.g., listen -> liston

failing to apply the rule of e (e.g., bike -> bik)reading one letter of vowel digraph (e.g., niece ->nice)

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• Surface dyslexia– other errors

stress shift errors: begin -> begginregularization errors: gone --> goan; pint --> pint with a short I

– insert Table 4.3 hereLint, flint, mint, pint, (note: sint)Other irregular words yacht

– In addition, to being a letter-by-letter reader, GM had surface dyslexia

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• Summary: Peripheral dyslexias– appear to be two distinct types of peripheral dyslexia

alexia without agraphiasurface dyslexia

– alexics appear to have damage to the word-form recognition system, and use a letter-by-letter processing strategy to compensate

– surface dyslexics may have damage to a system that translates graphemes into phonemes

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• Central dyslexias– Warrington has shown there are patients who

can read fluently phonologically and yet do not have semantic knowledge of the words that they are reading

– note: these patients appear to be able to read irregular words fairly well also

– these were patients with Alzheimer’s disease (AD)

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• Central dyslexias---spared phonological reading– Bub (1985) in a careful study showed that although

patient MP could read irregular words aloud, she was unable to understand their meaninge.g., on the Peabody test of word comprehension she

scored at the level of a 2.8 year old childin a word-word matching test - select an associate of the

target from among 4 items, she scored at chance (chair, apple, buy, pen: table)

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• Central dyslexias---spared phonological reading– Thus, these data suggest that it is possible to

access a phonological output representation of a word without being able to access the semantics of the word

– insert Figure 5.1 here

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• Central dyslexias--spared phonological reading– one way to account for this result is to assume

that visual input can be mapped into phonological output without entering into semantic memory

– see Figure 5.1

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• Central dyslexias--spared phonological reading– as Figure 5.1 shows it is assumed that visual input (a

written word) can access a visual input lexicon, which in turn can give rise to a phonological output lexicon without entering semantic memory

– alternatively visual input can access semantic memory (via a visual input lexicon) and/or can access the phonological output lexicon

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• Central dyslexias--spared phonological reading (summary)– other models have also been proposed to

account for this finding– what is common to each of these models is the

idea that visual input can be mapped into phonological output (speech) without having to go through semantic memory

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• Central dyslexias--deep dyslexia– the theoretical importance of deep dyslexia is

that it provides evidence that it is possible to access semantic memory via the orthographic route alone, rather than via the phonological route

– astonishing phenomenon (e.g., muddy --> quagmire)

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• Central dyslexias--deep dyslexia– types of errors made by deep dyslexics

semantic errors: ill--> sickvisual errors: life --> wifederivational errors: entertain -->entertainment

– effects of syntactic classnouns more likely to be read correctly than adjectives,

which were more likely to be read correctly than verbs, which were more likely to be read aloud than function words (e.g., prepositions and pronouns)

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• Central dyslexias--deep dyslexia– imageability

deep dyslexics are more likely to read highly imageable words than low imageable words

see Table 5.3 for a summary

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• Explanations of deep dyslexia– simplest explanation is that deep dyslexia occurs

when there is a relatively intact route from the visual word form to the semantic system, coupled with an impaired route from the visual word form to the phonological system

– See, for example Marshall & Newcombe model on next slide

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• Explanations of deep dyslexia– according to this account a visual word form elicits

a broad representation of meaning, not a specific specificationspecification sufficient to elicit concrete nouns, but not

to elicit abstract nouns, function words etc. Note: studies have shown that cognitively unimpaired

individuals are better able to retrieve the meaning of a word from its definition when the word is concrete than when it is abstract

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• Explanations of deep dyslexia– although other explanations of dyslexia have

been proposed, it appears that the data support the idea that it is possible to access semantic memory from an orthographic representation without having to access a phonological representation

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• Implications of acquired dyslexias for normal reading– the finding of letter-by-letter reading shows that people

with acquired brain injury may develop strategies of compensation that do not reflect normal cognitive processing of visual language

– thus, one needs to be careful in extrapolating from performance of brain injured patients to normals because brain-injured performance is not always just a ‘subtraction’

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• Implications of acquired dyslexias for normal reading– taken together the different types of dyslexia

support the idea that there are several different routes for reading wordsone route permits words to be read without being

understoodanother route permits visual word stimuli to reach

semantic systems without phonological mediation

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• A classic question in the psychology of language concerns the relation between the processes responsible for reading a word and writing a word– Dejerine in his investigations of alexia and

agaphia hypothesized that a single centre was responsible for both reading and writing

– insert Figure 4.1 here

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• Put more generally, one can ask whether the processes and representations used by input and output systems are the same or different– e.g., reading versus writing; speech perception

versus speech production; encoding versus retrieval (memory)

– it turns out that this question has proven to be difficult to answer

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• Why is this question difficult to answer?• Insert Figure 7.1 here

– Figure 7.1.I represents a common I/O system; 7.1.II represents separate I/O systems

– on the common I/O account a patient who has impaired performance at input and output has damage to the I/O system; dissociations between the two systems are accounted for by damage to the input (A) or output (D) systems

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– According to the separate system account similar degrees of impairment will occur when both systems are damaged, whereas dissociations between input and output are a reflection of selective damage to one of the I/O modules

– one pattern of performance that does appear to be difficult to account for in terms of the common I/O account is finding that some patients are impaired in their ability to repeat words (conduction aphasia)

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– Conduction aphasia. Patients have relatively well preserved language

comprehension and language production, but are impaired in their ability to repeat words

. Preserved speech comprehension suggests that the pathway into the input system is relatively intact; likewise preserved speech production suggests output system and speech is preserved

. Single i/o system would have to predict no impairment of word repetition

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– Another approach that has been taken to finding evidence for separability of input and output systems in reading and speaking has been to use a dual task paradigm

– the logic of using dual task is as follows:two routine but demanding tasks can be performed

well simultaneously if they are carried out by two separate functional subsystems (recall automaticity requirement)

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– It follows from this that if there are separate input and output systems, performance should be relatively well preserved under dual compared to single task conditions provided the two tasks engage different input and output systems

– In contrast, performance should deteriorate if the two tasks engage the same input or the same output systems

– Shallice, McLeod, and Lewis (1985) performed an experiment in which subjects performed tasks alone or concurrently

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– reading aloud (read and repeat words aloud)Visual input ortho input phonological output system (NOTE:

no semantic analysis)

– Word detection (listen to words and detect name)Auditory input phono input semantic system

– Reading aloud + word detectionTwo tasks are rel. independent, and hypothesized to use different

input and output systems. Hence there should be little interference. This result was obtained as shown in Figure on next slide

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Read aloud Shadow Name detection

Syllable count

Visual i/p Auditory i/p Aud. i/p Aud. i/p

Orthographic Phon. i/p Phon. i/p Phon. i/p

Phon. o/p Phon. o/p Semantic Phon. o/p

Read + name detection – little interference (diff. i/o systems)Read + syllable count – interference (same o/p system)Shadow + name detection – interference (same i/p system)Aud. = Auditory; Phon. = Phonological

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– Secondary tasks– Shadowing, hear words and repeat– auditory inputinput moduleoutput module– Shadowing should interfere with name

detection because both tasks require the input module

– Syllable counting should interfere with reading aloud because both tasks require output module

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Conclusion

if different i/o systems are engaged there is little interference (reading + name detection)

if similar input or output systems are engaged under dual processing there is considerable interference

these results suggest that input and output reading (input) and speaking (output) systems are involved

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– ConclusionsReading impairments (dyslexia) can be the result of a number of

specific impairmentsimpairments do not always ‘subtract’ cognitive processes (e.g.,

letter by letter reading)

– several different routes for reading wordsone route permits words to be read without being understood (AD

px)another route permits visual word stimuli to reach semantic

systems without phonological mediation(deep dyslexia)