phonology, dyslexia and the brain: a temporal sampling ... · power et al. 2016: impaired envelope...
TRANSCRIPT
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Phonology, Dyslexia and the Brain:
A Temporal Sampling Perspective
Usha Goswami
Centre for Neuroscience in Education
University of Cambridge
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Learning to read involves many senses …
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Predicting Reading & Dyslexia Across Languages
Brain
Language
Reading
Phonology
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Phonological Development: Levels of Analysis
Spoken
language
lexicon
Acoustics
Motor
Visual
Phonetics
Phonology
Sensory
Cognitive
Behaviour
“Phonological
awareness”
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Spoken/Written Language Processing
Lexicon/
Reading
Acoustics
Phonetics
Phonology
Psychology
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Psychology: Phonological Awareness
Shows Language Universal Development
(Ziegler & Goswami, 2005)
Preschool: large units
syllables
rhymes (onset/rime)
l – ast, bl - ast
With schooling: small units
phonemes b – l – a – s -t
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Spoken/Written Language Processing
Lexicon/
Reading
Acoustics
Phonetics
Phonology
Neuroscience
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The Brain and the Speech Signal:
Many Complementary Sensory Cues
Spectrogram e.g. phonetics
Amplitude modulation
e.g. prosody, rhythm
NINE SEVEN TWO THREE TWO
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Envelope and Fine Structure:
Envelope = power-weighted average
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Envelope: Importance of Rise Times
Modulation rates
cued in part by
rise times
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Envelope is of Key Importance to Speech Processing
Envelope studies: showed that brain could recognise
speech when very little or no spectral info. present
Recognition achieved on basis of envelope alone
(Shannon 1995 - amplitude/temporal cues)
Can also contrast envelope and fine structure – work
of Oxenham and colleagues
Language – envelope carries speech intelligibility
Music – fine structure carries the tune
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Auditory Chimera Sentences
Perception mainly from fine structure
Not much from envelope
Perception mainly from envelope
Not much from fine structure
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Envelope information most
important for speech intelligibility
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The Acoustic Signal: High Complexity
Spectrogram: emphasises formant structure
Amplitude modulation: emphasises speech rhythm
Low frequency envelopes are key structural cues
NINE SEVEN TWO THREE TWO
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The AE
Speech Spectogram
Child-Directed Speech: Nursery Rhymes
Leong, Stone, Turner, Gos 2014, JASA
Leong & Goswami 2015, PLoS One
AM Phase Hierarchy Models
Many amplitude envelopes
at different rates are
nested in the overall AE
(temporal rate)
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"Ma -ry Ma -ry quite con tra -ry"
‘STRESS’ AM ~ delta
(~2 Hz)
‘SYLLABLE AM’ ~ theta (~5 Hz)
‘ONSET/RIME’ AM ~ beta
(~ 20 Hz)
Leong & Goswami (2015)
Unpacking the AM structure of nursery rhymes
Spectral AM Phase Hierarchy: S-AMPH PLoS One
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Onset - rime
Syllable
Stressed syllable
GAR den
gar
g ar
den
d en
Universal Sequence of Phonological Awareness
Related to Nested AM Hierarchy in signal?
Leong & Goswami, 2015, PLoS One
~ 2 Hz
~ 5 Hz
~ 20 Hz
Acoustic hierarchy helps support phonological learning??
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Amplitude Modulations and Phonology
Brain
Language
Reading
Phonology
Amplitude envelope “rise times”
are strong cues to speech rhythm,
prosodic structure and syllable stress
Rhythm
Prosody
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How Does the Brain Encode Modulation?
Language
Representations
Neurons
Networks
Neuroscience
Simple neural coding
mechanisms, like
oscillation at different
rhythmic rates, appear
to be critical.
delta: 0.5 – 4 Hz
theta: 4 – 8 Hz
beta: 15 – 30 Hz
gamma: 30 – 50 Hz
Nested – delta at top
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Levels of Analysis
Phonological
difficulties
Amplitude
modulation &
rise time?
Rhythmic
difficulties?
Neural
Sensory
Cognitive
Brain Imaging –
Brain encodes energy
patterns or amplitude
modulations: oscillating
networks phase re-set
via ‘rise times’ in energy
(amplitude rise times)
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Speech signal
Rapid modulations
Gamma networks
~30 – 50 Hz
Slow modulations
Theta networks
~4 – 8 Hz
Binding for
speech perception
The Brain Samples Information in Different
Frequency Bands (delta, theta, gamma ..)
“syllables” “phonemes”
Poeppel
Giraud
Phase locking
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Speech signal
Rapid modulations
Gamma networks
~30 – 50 Hz
Slow modulations
Theta networks
~4 – 8 Hz
Binding for
speech perception
Is Phase Locking to Slower Modulations and
Rhythmic Events Impaired in Dyslexia?
Syllables (~ 5Hz) Phonemes (~35 Hz)
Slow modulations
Delta networks
~0.5 – 4 Hz
stressed
syllables (~ 2 Hz)
Rhythm
Syllables
Meter
Phonetic
information ?
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Envelope: Importance of Rise Times:
Acoustic Cue to Modulation Rates
Modulation rates
cued in part by
rise times
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Across Languages: Rise Time Impairments in DYS
English, French, Spanish, Hungarian, Chinese, Finnish…
… indicating speech envelope processing difficulties
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Rise time thresholds in infants at family risk for dyslexia:
Kalashnikova, Goswami, Burnham – in press
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Dyslexia: Rise Time and Phonological Skills
Across languages, children with dyslexia show:
Poor phonological awareness: stress patterns
syllables
rhymes
phonemes
Poor phonological memory: eg memory for digits
Poor rapid naming: naming pictures
naming colours
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Levels of Analysis
Phonological
difficulties
Amplitude
modulation &
rise time?
Rhythmic
difficulties?
Neural
Sensory
Cognitive
Role of rise time
sensitivity and
oscillations?
Dyslexia = difficulties
in recovering prosodic
(rhythmic) structure
from the speech signal?
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Do children with dyslexia have rhythmic
and prosodic difficulties?
Meter: Strong and weak “beats”
Music : Strong/
weak beats
Speech: Stressed/
unstressed
syllables
Amplitude
Envelope
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Metrical Musical Rhythms?
Rise time signals the attack time of
different musical instruments
Metrical same-different task: 2 Hz beat
3 / 4 time
4 / 4 time
Huss et al., 2011; Goswami et al., 2013, Cortex
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Musical Metrical Same-Different Task: 10 Yrs
10
20
30
CA DYS RA
No
. c
orr
ec
t/ 3
6
Correct responses
**
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Musical meter and reading
Reading R2 change sig
Step 1: age 0.03 ns
Step 2: IQ 0.03 ns
Step 3: metrical perception 0.42 .0001
Spelling
Step 3: metrical perception 0.28 .0001
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What about general rhythm perception?
e.g. tapping tasks
1.5 Hz (666 ms)
2 Hz (500 ms)
2.5 Hz (400 ms)
Thomson & Goswami, 2008
J. Physiology Paris (9 yr olds)
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Tapping to a Rhythm (1.5, 2 or 2.5 Hz)
(inter-tap interval variability)
0
10
20
30
40
50
60
1.5 Hz 2 Hz 2.5 Hz
tap
ra
te v
ari
ab
ilit
y (
ms
)
DYS CA
*
*
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Rhythmic tapping and reading
Reading % var sig
Step 1: age 0.08 .05
Step 2: IQ 0.18 .01
Step 3: tapping 0.15 .01
Spelling
Step 3: tapping 0.21 .01
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Dyslexia and Non-speech Rhythm
Children with dyslexia show rhythmic
impairments with musical rhythm and
when “tapping to the beat”
Perception on simple musical rhythm
and tapping tasks is a significant predictor
of reading development
Suggests rhythmic awareness and
phonology are related developmentally
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Prosodic (“Beat”) Structure in Language
e.g. “dee dee” tasks
“Jack and Jill went up the hill”
“Harry Potter”
Goswami et al. 2010, Reading & Writing
Goswami et al., 2013, J Memory Lang
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DeeDee Tasks: 12 Yr Olds
30
50
70
CA DYS RA
% c
orr
ec
t
nursery rhymes famous
**
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DeeDee Tasks: 9 Yr Olds
30
50
70
CA DYS RA
% c
orr
ec
t
famous
**
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Perceiving syllable patterning in speech
Children with dyslexia show sensory
impairments in perceiving prosodic
patterning (alternating strong and weak
syllables – “metrical structure”)
Suggests that prosodic / rhythmic perception plays
a key role in phonological development
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Speech signal
Rapid modulations
Gamma networks
~30 – 50 Hz
Slow modulations
Theta networks
~4 – 8 Hz
Speech percept
Phonetics:
ba - pa
Rhythm
Syllables
Meter
Role of Rise times/ Oscillations:
Dyslexia and atypical neural entrainment?
Slow modulations
Delta networks
~0.5 – 4 Hz
Temporal Sampling Theory (Goswami 2011, 2015)
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How Does the Brain Encode Modulation?
Language
Representations
Neurons
Networks
Neuroscience:
MEG
EEG Simple neural coding
mechanisms, like
oscillation at different
rhythmic rates, appear
to be critical.
delta: 0.5 – 4 Hz
theta: 4 – 8 Hz
beta: 15 – 30 Hz
gamma: 30 – 50 Hz
Nested – delta at top
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Entrainment to Speech by Children with
Dyslexia: AV, A, V Power et al., 2013
“ba ba ba ba ba ba..” (2 Hz rate)
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Significant difference in preferred phase in
the delta band for DYS vs control children:
Auditory and Auditory-Visual Conditions
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Delta band:
DYS = sig
entrainment
but different
preferred phase
DYS
CA
Power et al. 2013 – Phase of Entrainment Differences
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Power et al. 2013 – Impaired Oscillatory
Processes in Children with Dyslexia
Stimulus-induced modulation of oscillatory delta
processes functionally atypical in dyslexia
Rise time difficulties = brain less efficient at phase
resetting low-frequency oscillatory networks?
=> DYS entrain to a less informative portion of the
speech signal
Would affect perceptual organisation of speech at all
linguistic levels via the oscillatory (AM) hierarchy
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Power et al. 2016: Impaired Envelope
Encoding In Children with Dyslexia
Gave 200 semantically unpredictable sentences to
children
Speech degraded by noise vocoding (forces greater
reliance on envelope perception)
Measured quality of neural encoding of the
sentences using stimulus reconstruction in EEG
“Arcs flew their cough”
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Dyslexic children show poorer encoding of 2 Hz envelopes,
even when compared to RL controls (younger children)
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CA controls
Dyslexic
RL controls
Brain Response 0 – 2Hz
vs Stimulus Envelope
(black line)
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Onset - rime
Syllable
Stressed syllable
GAR den
gar
g ar
den
d en
Universal Sequence of Phonological Awareness
Related to Oscillatory Sampling Efficiency?
Leong & Goswami, 2015, PLoS One
~ 2 Hz
~ 5 Hz
~ 20 Hz
Acoustic hierarchy helps support phonological learning??
Oscillations = neural mechanism for mapping energy patterns
in the input (a hierarchical relational structure – delta at top)
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Educational Remediation?
Can musical and motor rhythms impact the
oscillatory networks for processing speech?
Music : Strong/
weak beats
Speech: Stressed/
unstressed
syllables
Amplitude
Envelope
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Bhide, Power & Goswami (2013)
Music+motor intervention for poor readers (10 weeks):
Drumming, singing, marching, poetry, hand-clap games…
Effect sizes:
Reading 0.73
NWR 0.95
Spelling 0.90
Rhyming 1.0
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Implications of TS Theory for Remediation
(Ideally prior to schooling)
“Entraining the oscillators” – use music + motor activities
to emphasise the rhythms and metrical structure of speech
- nursery rhymes
- poetry
- music and singing
Other rhythmic experiences:
- dancing
- marching
- playing instruments