What phonological deficit?
Franck Ramus and Gayanesh Szenkovits
Different theories regarding
developmental dyslexia
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Different theories co-exist in an attempt to capture the
mechanisms which cause developmental dyslexia- the
magnosystem hypothesis, the temporal processing
impairment and the phonological deficit theory. (Habib
2000)
Here we will focus on the phonological deficit theory and
try to present it in a different light.
In Ramus own words:‘’ The present paper is, at last,
about a first significant attempt to get to grips with the
phonological deficit’’
Phonological cognitive architecture
assumed
Banana
Ba
Ba
The 3 main dimensions to the
phonological deficit rolled into 1
1. Poor phonological awareness (phoneme deletion task say ‘rock’ without ‘r’ – ‘ock’).
2. Poor verbal short term memory( poor digit span 1425367 – 1425???).
3. Slow lexical retrieval ( rapid automatic naming task ….. Owl).
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The poor performance of dyslexics in verbal
tasks is related to one or more of these
dimensions.
 The three dimensions have something in
common: They all implicate phonological
representations, each in its own way.
The phonological representations
in developmental dyslexia are
degraded
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The most commonly accepted hypothesis regarding the
phonological deficit in dyslexia is that the phonological
representations are degraded (Fuzzier, or noisier, or are not
sufficiently categorical and preserve to many acoustic or allophonic details).
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Nevertheless, there is much more to phonology than
these three dimensions.
First, the locus and the nature of the phonological deficit
must be explicitly defined. Moreover, the vast knowledge
on phonology is seldom brought to bear on the
phonological deficit hypothesis. Secondly, the
phonological deficits predict deficits in heard language (
Ramus 2001).
In search of a locus-experiments
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In all the presented experiments, subjects are dyslexic
and non dyslexic adults.
In the first set of experiments, there was an attempt to
find the deficient levels of phonological representations
depicted in the suggested cognitive model.
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Lexical and sublexical levels were contrasted using words versus nonwords.( ton vs. zan)
 Input and output pathways were contrasted by comparing repetition (both)
tasks with auditory discrimination task (only input representations).
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Results show deficiency in both lexical and sublexical
levels and both pathways. Furthermore, a substantial
impairment in the input pathway. Short term memory
load was an important factor.
Representations vs. working
memory processes-experiments
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Why do dyslexics fail to discriminate and repeat verbal
material, when the short term memory load is
significant?
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Could be because their phonological representations are degraded.
Alternatively, it could the phonological representations are intact but the
short term memory is limited.
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An experiment of phonological similarity was run to
differentiate between the explanations.
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The more phonologically similar a sequence of words are the harder it is to
recall the sequence. If the phonological representations of dyslexics are
degraded ,there will be a different in the similarity effect compared to
controls.
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Dyslexics show the same similarity effect as controls.
Thus, short term limitations are argued for.
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Universal or hypernative
phonology-experiments
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Language specific phonological representations are
acquired very early in life by a child.( rice – lice)
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As the developmental dyslexia deficit is congenital, one known hypothesis is
that dyslexics incompletely acquire the specific phonological category of
their language. Thus, their phonology is less specific to any particular
language.( Mody et al 1997)
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Thus, one prediction is that dyslexics will be able to
perceive and perhaps produce foreign speech sounds.
An experiment was performed using dyslexic French
speakers, who were tested in discrimination and
repetition of foreign Korean voicing categories.
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Again there was an assessment of short term memory load, by
contrasting conditions of one foreign nonwords compared to
conditions with two or three nonwords.
Universal or hypernative
phonology-continued
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The results showed that dyslexic were similar in
performance to controls in single nonwords, but not in
the two or three non word sequence.
The results suggest that dyslexics are equally unable to
represent foreign speech sounds as controls. Group
differences appear only when short term memory load
increases.
Thus this is compatible to the hypothesis that
phonological representations of dyslexics are intact and
short term memory processes to operating on them
seem to be impaired.
Phonological grammar-experiments
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This is the whole host of rule like processes that apply in
speech production when phonological lexical items and
assembled to make phrases. These phenomena are
related also to speech perception, as an adaptation to
native phonological structure.
Most of these differences are language specific and
learnt during acquisition of language. Do dyslexic
children learn them as well as controls?
In one experiment, assimilations by phonotactic
constraints were investigated.
Phonological grammar- continued
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In English, clusters like [dl] or [tl] can never occur in the begging of a word.
The consequence is when subjects hear a non word such as [dla] or [tla],
they most often assimilate it to the closest legal cluster( [gla] or [kla])
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In such a discrimination task it was found that dyslexics
listeners fell victims to this perceptual illusion as much as
controls, hearing [gla] instead of [dla].
Thus, their speech perception is constrained by the
same phonotactic of their native language as controls.
In conclusion, the aspects of phonological grammar that
was investigated seem perfectly intact.
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Unconscious speech processingexperiments
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A problem in psycholinguistics is that tasks require
attention to the stimuli, and introspection, which may blur
the effects observed, particularly when the population
tested have problems with phonological awareness.
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Auditory masked priming have shown phonological lexical representations
processed unconsciously (hospital- nurse).
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A new question can be how efficient are unconscious
lexical access to phonological representations in
dyslexics?
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A masked priming tasks in dyslexics replicated the results of controls.
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The results support the notion that phonological
representation in dyslexics are not degraded and
dyslexics rely on them and not on the acoustical level.
A new hypothesis
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Findings converge to a conclusion: the phonological
representation of dyslexics are normal.
 Although, subjects do have a phonological deficit
measured by traditional tests: nonword repetition and
rapid naming tasks.
 It seems that short term memory load is paramount to
the deficiency of dyslexics in different tasks studied:
such as digit span or phonological awareness tasks,
which require holding segmented phonological units in
short term memory and conscious access to those
representations.
 An alternative explanation for the phonological task
deficits is phonological access.
A new hypothesis-continued
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Phonological access:
 Verbal short term memory requires access to
phonological representations to copy them into buffers,
then access for them retrieval, as well as to access input
representation to copy them to output representation.
 Phonological awareness tasks involve conscious access
to phonological representations, which may place special
demands on the system.
 Rapid naming tasks require fast access to lexical
representations.
 Thus, dyslexics seem to fail in tasks that are particularly
demanding in phonological access.
Discussion
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Are the subjects dyslexic enough? Yes, the subjects had
a history of reading disability. Furthermore, their
performance in phonological tasks (digit span, rapid
naming) did not match controls.
 Is working with adult subjects enough? It can be argued
that children may have deficient phonological
representations, but these are recovered in adulthood. A
replication study with children is needed. This criticism
steel don’t explain why representations have recovered,
and additional load on phonological access have not.
 Other past articles have been coarse in defining the
phonological deficit as shown here.
Discussion- continued
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Its seems that deficient phonological access can be
viewed as an executive function deficiency. This is a
specific type of executive function, specific in processes
and in modality.
 In relation to sensory theories, others have found that
dyslexic never seem to have a problems in perceiving a
certain kind of stimulus, be it auditory or visual: rather
the difficulty is related to task requirements, and
specifically to tasks that demand short term memory, or
when the stimulus is noisy.
 Dyslexic can be viewed as people with dysfunctional
sensory presentation access: most just to phonology and
others also to other domains: visual or auditory.
But…
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Dyslexia: a deficit in visuo-spatial attention, not in
phonological processing (vidyagaskar et al. 2010)
Speech Perception Abilities of Adults With Dyslexia: Is
There Any Evidence for a True Deficit?( Hazan
et al. 2009)
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