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Speech Perception Deficit in Children with Dyslexia

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Title: Speech Perception Deficit in Children with Dyslexia


1
Speech Perception Deficit in Children with
Dyslexia
S. MESSAOUD-GALUSI, V. HAZAN, S. ROSEN
  • Department of Speech, Hearing and Phonetic
    Sciences
  • UCL

2
The Research Project Why?
  • Many studies claim that a deficit in speech
    perception is at the heart of dyslexia
  • However other investigations found no speech
    perception deficit (Blomert et al. 2003)
  • Moreover, studies accounting for individual
    variability indicate that only a subgroup of
    dyslexics have difficulties (Adlard Hazan 1998,
    Manis et al 1997)

3
Theoretical Background Categorical Perception
  • Involves an acoustic continuum modelled on real
    syllables obtained by changing key acoustic
    elements in a gradual way
  • Pea Bee

4
Theoretical Background Identification
  • Extremes of the continuum are clearly labelled

5
Theoretical Background Identification
  • Intermediate stimuli are perceived as more
    ambiguous

Intermediary stimuli
6
Theoretical Background Identification
  • The listener labels the extreme and intermediate
    stimuli as belonging to different categories

Intermediary stimuli
7
Theoretical Background - Discrimination
  • When sounds labelled as pea are presented, they
    are difficult to discriminate

8
Theoretical Background Discrimination
  • When sounds are labelled differently, they are
    easy to discriminate.

9
Theoretical Background Identification in
Dyslexic individuals
  • They are less consistent in their identification
  • Dyslexic listeners typically show shallower
    identification slopes relative to average readers

AVERAGE READERS
DYSLEXICS
10
Theoretical Background Categorical Perception
in Dyslexia
  • Dyslexic listeners discriminate less differences
    between sounds from different category
  • Some suggest that dyslexic perceive better
    differences within the same category

AVERAGE READERS
DYSLEXICS
11
Theoretical Background Suggested link
  • Grapheme to phoneme correspondences require well
    segmented and distinct phonemic representation
  • Some studies suggest that poor phonemic
    representation as indexed by poor Categorical
    Perception in dyslexic individuals is linked to/a
    cause of reading impairments

12
Research questions
  • Is there a categorical Perception deficit in
    dyslexic individuals?
  • they should be poorer at CP tasks
  • Do they have problems processing speech in noisy
    environments?
  • They should be more affected by noise in CP task
  • Recognition of isolated words with noise in the
    background should be harder

13
Research questions
  • What is the prevalence of speech perception
    deficit in dyslexic children?
  • What is the consistency of the speech perception
    deficit in dyslexics
  • we tested the same skills in different but
    related tasks.

14
Population
  • 113 children recruited
  • 62 formally diagnosed dyslexic
  • 51 average readers matched in age
  • Between 6.6 and 13.7 years old
  • Monolingual native English speakers
  • Normal auditory threshold (audiometry)
  • Not language impaired or ADHD

15
Baseline Tests
  • All within normal range (gt85)
  • verbal and non-verbal IQ (wisc, BPVS)
  • receptive grammar (TROG)
  • Reading and phonological processing tests
  • Reading
  • Phonological awareness
  • Phonological STM

16
Experimental Tests Identification Task
  • In quiet and in noise at 6dB Signal to Noise
    Ratio background babble noise
  • Throughout the task the VOT was varied adaptively

17
Experimental Tests Discrimination Task
  • Listener presented with 3 frogs
  • Listener clicks on the frog that says something
    different
  • 3 tasks testing across and within phonemic
    category discrimination in quiet
  • 1 task testing phonemic discrimination in noise

pi
pi
bi
18
Experimental Tests Within and Across Category
Differences
  • Adaptive task
  • WITHIN Standard stimuli always pea, comparison
    stimuli starts at bee and changes to pea in quiet
    and with noise in the background
  • ACROSS Pea and Bee across boundary in quiet

pi
pi
bi
19
Experimental Tests Across and Within Category
  • Fixed set of stimuli
  • Fixed pea and bee stimuli differing in 15 and 20
    ms VOT
  • Within and Across category
  • Fixed task Adaptive task

pi
pi
bi
20
Experimental Tests - Speech in Noise
  • Words in Noise
  • Highly familiar words presented with noise in the
    background
  • Signal to Noise Ratio (SNR) varied adaptively
  • Increase after a correct repetition
  • Decrease after an incorrect repetition

21
Experimental Tests - Speech in noise
  • The colours and numbers change
  • SNR varied adaptively

22
Results identification of /pi-bi/ in quiet
  • Groups differ in slopes

23
Results identification of /pi-bi/ in quiet
AVERAGE READERS
DYSLEXICS
  • Catch trials
  • Well identified by most listeners at the start of
    the task
  • As the task goes, dyslexics make more errors in
    identifying catch trials, showing an effect of
    fatigue

24
Results identification of /pi-bi/ in noise
  • No significant difference between groups in noise
  • Greater effect of noise in controls than in
    dyslexics

25
Results identification of /pi-bi/ in quiet and
in noise
  • In quiet, poorer identification and poorer
    attention in the dyslexic group relative to
    controls.
  • In noise, no greater effect of noise in the
    dyslexic group but greater effect of noise in the
    control group

26
Results Discrimination within - adaptive
  • The dyslexic children
  • are WORSE at perceiving
  • within category differences
  • than the controls

27
Results Discrimination across - adaptive
  • Surprisingly, no difference between groups

28
Results Discrimination in noise
  • Both groups are
  • WORSE in noise
  • The dyslexic children
  • are POORER than controls

29
Results Discrimination within/across - fixed
  • Within category no group difference
  • Across category dyslexics were significantly
    poorer than controls

30
Results Speech in noise
  • No group differences

31
Results Prevalence of poor perceivers in the
participants
  • Identified participants scoring below the 1.65 SD
    of the controls
  • That is the 5th percentiles
  • In a consistent set of tasks 3 or more
  • 12 of the dyslexics and 9 of the controls
    identified as poor perceivers
  • Also 33 of the dyslexics and 68 of the controls
    within norm in all the tasks

32
Results Summary
  • No consistent difficulties in categorical
    perception in the dyslexic group
  • The presence of noise did not systematically
    affect the dyslexic more than the controls
  • Group differences may be due to poor attention
  • Only a small proportion of the dyslexic children
    had consistent difficulties with speech while
    some did not have any at all

33
Conclusion
  • Speech perception difficulties do not
    systematically lead to reading difficulties
  • Reading difficulties are not systematically
    linked to poor speech perceptual skills
  • Speech perceptual difficulties does not explains
    reading deficit that dyslexic individuals suffer
    from
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