Download 2. Acquired dyslexias

PS2011 & PS2016 Cognitive
Psychology – Dr John Beech
The Acquired Dyslexias
The acquired dyslexias
Introduction
• They are sometimes known as the “alexias”.
• The acquired dyslexias are usually acquired as a result of
brain damage; but a couple of them can also be used to
describe processes that have failed to develop.
• In a sense these are syndromes, ie they each have a
collection of symptoms, but there is a great deal of
variation so that individuals may not fit neatly within.
• What follows is just a brief overview of 4 of the acquired
dyslexias:
1. Phonological dyslexia
2. Deep dyslexia
3. Surface dyslexia
4. Letter-by-letter dyslexia.
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Phonological dyslexia: symptoms
• This condition was first described by Beauvois & Derouesne
(1979) and occurs both in acquired dyslexia as well as in
developmental dyslexia.
• We start here as it is a very common dyslexia as many children with
reading problems appear to have some form of phonological
dyslexia. The basic aspect is that there is a major problem with
reading nonwords (e.g. glip, trank) compared to reading ordinary
words and problems with unfamiliar words.
• A noteworthy aspect (to separate it from deep dyslexia—to follow) is
that there is some degree of ability to read nonwords. Those with
Phonological Dyslexia (PD) do not find it completely impossible. By
contrast in deep dyslexia nonword reading is impossible.
• Reading of words in (PD) varies between 50-100% in tests.
• Some PD cases also show overlap with deep dyslexia, so there is
some fuzziness.
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Phonological dyslexia: symptoms
• Reading errors in PD are usually either derivational (e.g. woman –
‘women’; think – ‘thought’; leave – ‘left’) or visual (e.g. band –
‘bend’; panda – ‘ponds’). Obviously a better reader will commit
fewer errors of this type.
• Some with PD have function word problems (e.g. an – ‘and’; is –
‘his’). Others apparently have no such problems. But even these
may have great problems reading function words in text even
though they can read them in isolation.
Theoretical interpretation
There appears to be damage to the non-lexical (phonological) route:
Abstract
letter
Identification
Letter-tosound
rules
Phonological
output
buffer
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Phonological dyslexia: causes
• There could be damage to any part of this route. But
although such damage means that reading nonwords is
very difficult, there should be no problem with real words.
This is because they can be read by means of a lexical
route (ie. reading by accessing word units), as in the
dual-route theory of reading.
• Coltheart (1985) proposed that the precise location of
such damage in PD determines the type of PD. For
instance, some have problems with strings of letters and
converting these into graphemes (e.g. SH-O-CK – 3
graphemes out of 5 letters). Children with PD invariably
have problems with phonics.
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Deep dyslexia - symptoms
• All patients with deep dyslexia (DD) have had considerable damage
to their left hemisphere. This produces aphasia* and hemiparesis*.
• Patients have a considerable number of problems, esp. in reading:
Semantic errors (weigh – “anchor”; brown – “black”).
Nonwords (e.g. blard) are not read or mistaken for a real word
(“lard”)– called lexicalization.
Function words (e.g. the, or, also).
Visual errors (e.g. band – ‘bend’; panda – ‘ponds’).
Concreteness: Concrete nouns (e.g. table, phone) are read
better than adjectives, verbs and abstract nouns (e.g. humour).
Morphological errors where the root of the word is correct, but the
affix is wrong (e.g. blender – “blend”; unkind – “kind”
Writing may be impossible because of the hemiparesis.
*Aphasia = loss of language production
*hemiparesis= partial paralysis to one side of the body
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Deep dyslexia: its cause
• Coltheart (1980) has proposed that DD is unique
because it is not using a damaged reading system,
instead the whole of the left hemisphere is out of
commission. This means that only the right hemisphere
is used for reading.
• Patterson et al. (1987) in support of this reports a case
whereby because of abnormalities, a 15-year-old had
her left hemisphere removed. Before she was a normal
reader, but after she had all the major symptoms of DD.
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Surface dyslexia: symptoms
• The major characteristic is sensitivity to spelling
regularity. Thus there are no problems with regularly
spelled words (e.g. hint), but considerable problems
reading irregularly spelled ones (e.g. pint, choir,
island).
• When making these errors those with surface dyslexia
(SD) consider that what they say is the actual word. E.g.
shoe will be read as “shO” (as in show) and the reader
will think the word is actually show.
• The length of words affects the reading time in SD.
• Nonwords – do not pose any problems.
• There are none of the symptoms of phonological or deep
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dyslexia.
• SD suggests reading by
applying letter-sound
rules. So irregular words
(also known as exception
words) produce
regularization errors (e.g.
choir – “choy-er”). This
in turn suggests damage
to a lexical route—a
route involving
processing word units.
• The figure shows KT
(McCarthy &
Warrington, 1986) who
has pure SD although
some exception words
are read accurately,
performance is a lot
worse than for regular
words.
Surface dyslexia:
interpretation
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Surface dyslexia: interpretation
• KT suffered from semantic dementia due to deteriorating
temporal lobes. Thus semantic knowledge was
deteriorating. This probably accounts for deterioration in
processing word units, but a relatively intact letter-sound
translation system.
• An alternative interpretation for SD, probably less plausible,
is that word analogies are being used inappropriately (e.g.
Patterson, 1981). For instance, broad is pronounced as
“brode”, because of the embedded word road.
• Developmental surface dyslexia is also in evidence
(Castles & Coltheart, 1984). These are children who have
grasped phonics relatively easily, but find it difficult to
develop their sight vocabulary. They too make
regularisations when encountering irregular words.
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Letter-by-letter reading: symptoms
• Otherwise known as pure
alexia.
• As implied by the name, words
and nonwords are read letter
by letter. In practice this
means that they are spelled
out aloud (e.g. “n-u-t-m-e-g…
nutmeg”). (The spelling part is
aloud, whispered, mouthed or
silent.)
• As might expected this means
very slow reading times that
increase as a function of word
length as shown on the right.
• Single letter reading is usually
OK, but some patients make
errors (rind – “r-i-n-g…ring”).
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Letter-by-letter reading: symptoms
• There are no problems in writing. But because of the
condition after a patient has written something they can’t read
it, which is very frustrating. Cursive handwriting is particularly
difficult for them as the individual letters are not separated.
• Understanding of language and producing language is
normal.
Areas of damage
Lesions are in two sites…
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Letter-by-letter reading: symptoms
Areas of damage
Lesions are in two sites:
1. Left occipital region – this results in right hemianopia*. This
effectively disables normal reading ahead. Psychologists can
present words to the left visual field.
2. The splenium - posterior of the corpus collosum.
Both these lesions are usually present. In normal functioning
(ie. NOT in L-by-L) words to the right visual field are
processed by the left visual cortex and then the splenium
transfers information between the hemispheres. But
obviously in L-by-L this can’t happen. The result is the slow
letter-by-letter reading.
*Hemianopia = inability to see a visual field, in this case to the
right of fixation.
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Letter-by-letter reading: unconscious reading
• There is anecdotal evidence that soon after initiating the
spelling out of the words L-by-L patients actually know
what it is.
• To test this Shallice & Saffran (1986) presented words
and nonwords briefly (1-2 sec durations) and asked them
to guess if it was a word or nonword. Reluctant to do
initially, but they score well above chance indicating that
semantic information is available.
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Summary of 4 acquired dyslexias
Types of dyslexia
Phono
Deep
Surface
L-by-L
1. Word v. nonword
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2. Spelling regularity
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3. Word length
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4. Concreteness
?
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5. Content v. function
?
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6. Semantic errors
?
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
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