surface dyslexia

dyslexia

1. SURFACE DYSLEXIA
PRESENTED BY:
Ms Akanksha Gupta
Mr. Sunil Kumar

2. Dyslexia
•Acquired dyslexia refers to individuals who, as a
result of brain injury or neurologic condition, are
unable to perform normally on reading or writing
tasks, whereas pre-morbidly their reading and
writing performance was entirely normal (Coltheart,
1981).

3. •The study of the acquired dyslexia or reading
disorders is basically done on neuro-anatomical
and the general cognitive grounds.
•Neuro-anatomical approach- correlate specific
disorders of reading with specific lesions of the
brain and,
•General cognitive approach - effects of damage to
a general cognitive process such as visual
perception on a more specific task such as
reading.

4. •In accordance with the model building approach,
the study of cognitive functions (such as reading)
are approached with a specific theoretical model
consisting of explicit sets of processing stages
connected by a network of pathways.
• Disorders of reading are then explained, in terms of
impairment in one of the processing stages in
these multi-component models.

5. •The analysis of reading disorders with-in the format
of these models has resulted in the identification of
specific subtypes of acquired dyslexia such as
pure alexia or letter-by-letter reading, deep
dyslexia, surface dyslexia, phonological dyslexia,
attentional dyslexia, and neglect or positional
dyslexia.
•They can be classified as follows:

7. Definition
•Surface Dyslexia, which is similar to visual dyslexia
in other sub typing systems, is a subtype of
dyslexia characterized by a difficulty in the
lexical access of word meanings.
•This means that surface dyslexics are able to
recognize that printed words are words, but are not
able to access the definitions from within their
internal lexicon by way of the visual image of the
printed word.

8. •Surface dyslexia is an acquired disorder of reading
and writing of central origin.
•Surface dyslexics do however process auditory
words with little difficulty, and possibly with greater
speed and efficiency than normal non-surface
dyslexics.

9. •Subjects with surface dyslexia often fails to
recognize words directly and has to resort to
reading words aloud by working out their letter-
sound relationship or using analogies with similar
words.

10. •In languages like English, this leads to disordered
reading of irregular words.
• Spelling is also impaired and generally the
misspelled words are phonetically correct. (e.g.,
the client reads /steam/ aloud correctly while
pronouncing /steak/ as /steek/.

11. Symptoms of surface dyslexia

•About three-quarters of the words of English are
regular words. This term refers to words which obey
the standard spelling-to-sound rules of English.
•The remaining 25% or so of words are irregular
words, also referred to as exception words; such
words contain at least one violation of English
spelling-to-sound words. Examples are pretty and
bowl.

12. The defining symptoms of surface dyslexia are:
•Exception words are less often read correctly than
regular words when on word frequency, number of
letters, etc
•When an exception word is misread, the error is
generally a regularization error i.e. the
pronunciation given is the one specified by the
rules.
•For example, pretty is read as if it rhymed with
"jetty", and bowl is read as if it rhymed with "howl".

13. The common feature which defines these patients is
•their ability to attach semantics directly to the
printed words,
•their reduced capacity to access whole-word
phonology and
• their over reliance on relatively well preserved
grapheme-phoneme correspondence for sub word
length letter groups.

14. Surface dyslexia in adults is characterized by
the tendency to read words using letter-sound
rules.
They read regular words more easily than
irregular words and many of their reading errors
are regularization. These occur when irregular
words are decoded using phonological rules.
For e.g., ‘broad’ might be read as ‘brode’ and
‘great’ as ‘greet’.

15. •Additionally because surface dyslexics read sound
by sound they are prone to confuse the
meanings of homophones such as ‘fair’ and ‘fare’,
‘leek’ and ‘leak’, ‘meddle’ and ‘medal’ and they have
marked difficulty in understanding what they
read.
•Unlike phonological dyslexics, one aspect of their
reading which is intact is their non-word reading.

16. The theoretical interpretation
of surface dyslexia
•Because the non-lexical route reads by applying
letter – sound rules, it will misread words that don't
obey those rules; indeed, it will produce
regularization errors with such words.
•Therefore, according to the DRC model, correct
reading aloud of exception words depends upon
the lexical reading route.

17. •Hence damage to the lexical route will result in
surface dyslexia: non-words (and regular words) will
still be read correctly, but exception words will often
result in regularization errors.

18. •Since the lexical route has a number of different
components, there are a number of different
ways in which it can be damaged so as to produce
surface dyslexia, and so any two patients with
surface dyslexia may have quite different patterns
of damage in the lexical route.

19. •Two examples of such damage are :
1.Damage to entries in the Orthographic Input
Lexicon , and
2.Damage to entries in the Phonological Output
Lexicon.

20. •If the word ‘pretty’ has
been lost from the
Orthographic Input
Lexicon, it won't be
recognized lexically,
so will be read non-
lexically and so will
be regularized.
•If it has been lost from
the Phonological
Output Lexicon, it will
be recognized when it
is seen, but its
pronunciation won't be
retrieved from the
Phonological Output
Lexicon, so will have to
be generated non-
lexically - so again a
regularization error
will occur.
Orthographic
Input
Lexicon
Phonological
Output Lexicon

22. • KT was a case of “progressive semantic
deterioration with semantic dementia" (progressive
loss of semantic knowledge due to progressive
atrophy of temporal lobes), so, surface dyslexia was
also seen.

23. •In such cases, the surface dyslexia is presumed to
be due to an impairment of - entries in, or access
to, the Phonological Output Lexicon that
accompanies the semantic impairment.

24. Developmental surface dyslexia
•Holmes (1973) and Coltheart et al, (1983) have
described cases of developmental surface
dyslexia, and have shown that this form of
developmental dyslexia is not uncommon (Castles
and Coltheart 1994)

25. •They have no troubles with the phonic side of
reading and quickly learn to sound out words by
letter-sound rules.
•But have problems in learning to read that is in
developing sight vocabulary.

26. •They recognize quite fewer words than other
children their age who are making normal progress
in learning to read , by sight .
•Hence many exception words which the normal
children can read aloud correctly will be regularized
by the developmental surface dyslexic.

27. Distal Causes of Surface dyslexia

But, it is not possible to generalize with confidence
from these scans (Vanier & Caplan, 1985).
left hemisphere
lesions
wide variety of
lesion sites
acquired
surface
dyslexia SBAMTkYP
anSDYhETP
surface
dyslexia

28. •Surface dyslexia can result from a number of
different lesions in different parts of the functional
reading system.
•If the functional modules of that system map onto
different anatomic modules, then lesions in a
number of different parts can be distal causes of
surface dyslexia.

29. Also, Surface dyslexics' difficulties seems to coincide
with abnormalities in the left temporal lobe;
•where are found reduced usage patterns (Flynn,
Deering, Goldstein, and Rahbar, 1992) and
•atypical symmetry of size compared to the right
temporal region (Collins and Rourke, 2003).

30. •Surface dyslexics have difficulty recognizing text
objects. This can be explained logically as many
areas of left temporal region are recruited for
object recognition (Gazzaniga, Ivry, Mangun
1998) and
•What appears to be diminished use and capacity
are unusual usage patterns of both the left
temporal lobe and the angular gyrus (Collins and
Rourke, 2003).

31. •This is assumed to be correlated with poor or
dysfunctional connections between many of
these areas (Collins and Rourke, 2003).
•The findings lend credibility to the notion that
surface dyslexics are not able to connect text
images to their meanings, and must connect
them through unique pathways.

32. The role of visual factors in dyslexia
•Just like the language impairment seen in dyslexic
children, it is important to understand the precise
nature of their reading and spelling difficulties, so
their visual processing skills should also be
taken into consideration.

33. •As yet there is no conclusive evidence that visual
processing impairments on their own cause
dyslexia.
•But this does not rule out the possibility that such
difficulties might compound the reading problem.

34. •It is conceivable that visual skills contribute to the
development of reading- this is particularly
important in children with language difficulties in
providing an alternative set of compensatory
strategies for them.

35. There are 2 main strands to current
research on visual factors in dyslexia
1.Stein, 1991, has suggested that dyslexic children
have deficient ocular motor control.
They Dunlop test as part of an orthoptic
assessment and shown that fewer dyslexic children
have an established reference eye than normal
readers.

36. •They recommend monocular occlusion as a
means of encouraging binocular control and
facilitating learning to read. (Bishop, 1989).

37. 2. Lovegrove and Williams, 1993 said that dyslexic
children have low level impairments of the transient
visual system.
•Such difficulties would lead children to experience
blurring of print and thus affect their reading, but
unlike the data on phonological deficits, there is no
evidence to suggest that this visual impairment are
causally related to reading problems.

38. Types of Surface Dyslexia
•Surface dyslexia also illustrates the issue of
variability within a deficit syndrome, as it
fractionates into 2 subtypes,
othe “dysfluent” type and
osecond type that Patterson et al (1989) termed
“fluent surface dyslexia”

39. Dysfluent surface
dyslexia
•It can be simulated
by damaging the
orthographic-
phonological (OP)
computation as
implemented, while
the fluent pattern
cannot.
Fluent surface
dyslexia
•Shows
mispronunciations of
irregular words more
than regular words
or non-words.
•Errors were
frequency sensitive,
with only lower-
frequency items
affected more.

40. Dysfluent surface
dyslexia
Fluent surface dyslexia
•Naming latencies are
within normal limits for
older subjects.
•Finally all errors were
simple regularizations,
for e.g., “have”
pronounced “haive”
and “deaf’ pronounced
“deef”.

41. •This suggests that the 2 patterns have different
sources.
•One possibility is that the fluent surface dyslexic’s
performance reflects the intact operation of the
OP computation (unlike the dysfluent);
the brain injury eliminates contributions from the
orthography-semantics-phonology (OSP)
computations.

42. •The division of labor in the Seidenberg and
McClelland (1989) model is that OP produced
correct output for both high and low frequency
regular words and high frequency irregular words.
•These are the items that surface dyslexic patient
misses. Thus, their performance appears to result
from an intact OP computation with impaired input
from OSP.

43. Thus it can be concluded that

45. • This analysis of surface dyslexia provides
illustration of the differences between the:
Dual-route
model
Connectionis
t model

46. In the dual-route model

47. •It explains how a given type of error can arise
from multiple underlying causes.
•Thus, error on irregular words arose from
both:
.
In connectionist model

48. •Thus, the properties of the computations
within different components of the
connectionist network and,
• the division of labour between them
provide a basis for understanding 2 very different
“surface dyslexic” profiles.

49. Dysfluent type Fluent type
Errors on exception words

Errors on exception
words
Some regularization errors,
also “visual” errors
Errors almost all
regularizations
Also makes errors on
regular words

Very accurate on
regular words
Errors are not frequency
sensitive
Errors are frequency
sensitive
Nonword reading is impaired

Nonword reading is
accurate
Latencies abnormally long

Latencies within normal
limits
Semantics is largely intact Semantics is grossly
impaired

50. THANK YOU !!