Speech Perception Deficit in Children with Dyslexia

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Speech Perception Deficit in Children with
Dyslexia
S. MESSAOUD-GALUSI, V. HAZAN, S. ROSEN

• Department of Speech, Hearing and Phonetic
  Sciences
• UCL

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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)

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Theoretical Background Categorical Perception

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

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Theoretical Background Identification

• Extremes of the continuum are clearly labelled

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Theoretical Background Identification

• Intermediate stimuli are perceived as more
  ambiguous

Intermediary stimuli
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Theoretical Background Identification

• The listener labels the extreme and intermediate
  stimuli as belonging to different categories

Intermediary stimuli
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Theoretical Background - Discrimination

• When sounds labelled as pea are presented, they
  are difficult to discriminate

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Theoretical Background Discrimination

• When sounds are labelled differently, they are
  easy to discriminate.

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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
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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
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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

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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

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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.

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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

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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

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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

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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
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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
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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
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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

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Experimental Tests - Speech in noise

• The colours and numbers change
• SNR varied adaptively

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Results identification of /pi-bi/ in quiet

• Groups differ in slopes

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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

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Results identification of /pi-bi/ in noise

• No significant difference between groups in noise
• Greater effect of noise in controls than in
  dyslexics

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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

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Results Discrimination within - adaptive

• The dyslexic children
• are WORSE at perceiving
• within category differences
• than the controls

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Results Discrimination across - adaptive

• Surprisingly, no difference between groups

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Results Discrimination in noise

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

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Results Discrimination within/across - fixed

• Within category no group difference
• Across category dyslexics were significantly
  poorer than controls

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Results Speech in noise

• No group differences

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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

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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

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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