AS14.1 – The Role of Neural Oscillations in Auditory Resolution and Speech Perception – Implications for CAPD, Phonological Awareness and Reading Disorders Presented by Sharon Cameron National Acoustic Laboratories Date: 11 December 2014 Time: am Location: Denis Byrne Seminar Room Fabrice Bardy Harvey Dillon Tim Beechey Nicky Chong-White

Overall Aim To investigate the relationship between speech perception and the ability of the central auditory nervous system to sample and process rapidly- changing frequency and amplitude information contained in an incoming acoustic signal.

Hypotheses Neural oscillations enable sampling of the incoming acoustic signal that enables:  identification of changes in amplitude, which is critical for parsing the speech stream into syllabic units; and  adequate sampling of speech during periods of rapid spectral variation.

Hypotheses In some children with CAPD, phonological awareness and reading deficits, neural oscillation are:  not sufficiently powerful or synchronised at important frequency ranges, or  are inappropriately balanced across the brain hemispheres.

Hypotheses  This results in inefficient sampling of the acoustic signal and thus an unclear or “fuzzy” representation of the incoming sound.  This may, in turn, lead to creation of poorly-defined stored phonemic representations, difficulties matching the identifying features of the acoustic signal to stored templates, or a deficit in parsing the speech stream into syllabic units.

Specific Aims 1.Development of two behavioural tests to assess participants’ identification skills for (a) fast formant transitions and (b) amplitude modulation (syllable parsing). 2.Development of EEG (and potentially MEG) test stimuli and analytical protocols for assessment of spontaneous, evoked (time locked) and induced neural oscillations. 3.Assessment of 150 typically developing and a-typically children (CAPD; phonological awareness and reading deficits) on a range of assessments.

Cognition memory, IQ, attention (TAPS-3; WNV; TEA-Ch Sentence perception Sentences in competing noise (LiSN-S) Auditory resolution Formant Transition (FT) Detection Amplitude Modulation (AM) Discrimination (syllable parsing) Neural oscillations Evoked & spontaneous (delta, theta, alpha, beta, gamma) EEG/MEG Reading Non-word versus irregular word (CC2) Phonology Phonemic & phonological awareness (CTOPP) γ δ, θ δ, θ, γ α, β Structural Equation Modelling

Objective The development of clinical protocols and tools that will allow identification, and differential diagnosis, of deficits in speech perception, auditory processing, phonological awareness and reading, where the underlying cause is related to the resolution with which the auditory signal is analysed by the brain.

Behavioural Experiments

Behavioural Phoneme Identification Test – Stimuli Synthesized (Praat) stimuli along /ba/-/da/ continuum presented in random order: Part 1 (44 stimuli): 11 steps: [0, 10, 20, 30, …, 90, 100]% da 4 presentations of each Part 2 (48 stimuli): 7 steps: [0, 100]% da + 5 steps around threshold (between 1-99% of psychometric function) o 4 presentations [0, 100%] da o 8 presentations of others

/ba/-/da/ Categorisation Stimuli 50% 100% /ba/ 100% /da/ 60% /ba/ 60% /da/ Initial F2 frequency interpolated from 100% /ba/ to 100% /da/. F1, F3, F4 transition do not vary between stimuli.

2AFC Phoneme Identification Test - GUI Practice Session: 5 x /ba/ 100% 5 x /da/ 100% Test Session: 92 stimuli Participant presses BA or DA button depending on what phoneme they heard.

Phoneme Identification Test - Scoring Alternate stimuli assessed for test-retest reliability. Psychometric function fitted to data to find threshold. Reaction time, and number of repeats measured for each stimulus.

Results: /ba/-/da/ Categorisation (n = 10 TD Adults) Number of times participants press /ba/ divided by total number of presentations at each step size. Change in second formant frequency from 100% /ba/ to 100% /da

Results: /ba/-/da/ Categorisation (n = 1 TD Adult)

Behavioural Amplitude Modulation Detection Test - Stimuli Synthesized (Praat) steady state vowel [a:]. Two and three syllable stimuli with varying amplitude modulation depths are presented in random order. Part 1 (44 stimuli) : 11 steps: [0, 10, 20, 30, …, 90, 100]% modulation depth (x 2 and 3 Syllables). 2 presentations of each Part 2: (48 stimuli) 7 steps: [0, 100]% + 5 steps around threshold (between 1-99% of psychometric function) o 2 presentations [0, 100%]: x 2/3 syllables o 4 presentations of others: x 2/3 syllables

Amplitude modulation stimuli: Synthesized [a:] – Three syllables 100% AM 10% AM Unmodulated 50% AM

100% AM 10% AM Unmodulated Amplitude modulation stimuli: Synthesized [a:] – Two syllables 50% AM

3AFC Amplitude Modulation Detection Test - GUI Practice Session: 3 x 100% AMD (2&3) 3 x 0% AMD (2&3) Test Session: 92 stimuli Subject presses “ 1 ”, “ 2 ” or “ 3 ” depending on how many syllables they heard. A small amount of AMD will sound like 1 syllable.

Modulation Identification Score: o Modulation identified = score of 1 o Modulation not identified = score of 0 o Incorrect number of syllables identified (2 vs. 3) = score of 0.5. Alternate stimuli assessed for test-retest reliability. Psychometric function fitted to data (2 and 3 syllable responses combined) to find threshold Reaction time, and number of repeats measured for each stimulus. Behavioural Amplitude Modulation Detection Test - Scoring

Results - 3FC Amplitude Modulation Detection Test (n = 5 TD Adults) Modulation identification score divided by total number of presentations at each step size. Change in amplitude modulation depth from 0% to 100%

Results - 3FC Amplitude Modulation Detection Test (n = 1 TD Adult)

Normal categorical perception What do we expect to see in our clinical vs. TD children?

Most of the acoustic space is categorised Ambiguous/speech error Discrete, non-confusable phonemes

Continuous perception Over-sampling hypothesis: redundant acoustic details are perceived

No discrete categories Over-sampling hypothesis: redundant acoustic details are perceived

Under-sampling hypothesis: Only canonical/endpoint tokens are categorised Otherwise chance performance Add Noise?

Very little acoustic Space is usable Discrete categories if acoustic input is canonical. Categorisation is affected by any degradation of the Signal.

Proposed EEG/(MEG?) Experiments

Brain oscillation reflecting computation in the brain Delta (1-3 Hz) Δ or δ Theta (4-8 Hz) θ or ∅ (Intrinsic/obligatory brain activity) Alpha (10-14 Hz) α Beta (18-22 Hz) β Gamma (30-60 Hz) γ δ θ α β 1 β 2 γ 1 γ 2 γ 3 γ 4

Frequency Coupling Delta -Theta / Beta => prediction (e.g. rhythm) For example, the phase relationship and/or amplitude ratio between oscillatory bands δ θ α β 1 β 2 γ 1 γ 2 γ 3 γ 4

Delta -Theta / Beta => prediction (e.g. rhythm) Theta / Gamma => sampling (e.g. acoustic encoding) Frequency Coupling

δ θ α β 1 β 2 γ 1 γ 2 γ 3 γ 4 Alpha => attention Brain oscillations reflecting computation in the brain

EEG paradigm 1 – Phoneme Identification Active Listening Paradigm 1.EEG cap recording 64 electrodes (Neuroscan). 2.Stimuli presented over insert earphones in sentence form, e.g. “I saw BAWA/DAWA eating chips.” 3.Question presented, e.g. “Who is eating chips?” 4.Participant uses response button to answer “BAWA or DAWA”. 5.Stimuli are 100%/70% [ba]; 100%/70% [da]. Passive Listening Paradigm: All 4 stimuli randomly presented. 2 Conditions: -Active listening - button press – Stim 1: BAWA or DAWA (who is eating chips?) Stim 2: 100%/50%/0% (1 or 2 Syllables) -Passive listening

I saw DAWA eating chips (100%) I saw BAWA (100%) eating chips EEG Auditory Stimuli – Phoneme Perception Stimuli Synthesized speech in Praat 100% [da] 70% [da] 100% [ba] 70 % [ba]

EEG paradigm 1 – Amplitude Modulation Detection Active Listening Paradigm 1.EEG cap recording 64 electrodes (Neuroscan). 2.Single amplitude modulated vowel /a:/ presented over insert earphones. 3.Response button used to indicate whether 1 or 2 syllables were heard. 4.Stimuli are: 100% amplitude modulation depth (2 syllables) 50% AMD 0% AMD (1 syllable). Passive Listening Paradigm: All 4 stimuli randomly presented. 2 Conditions: -Active listening - button press – Stim 1: BAWA or DAWA (who is eating chips?) Stim 2: 100%/50%/0% (1 or 2 Syllables) -Passive listening

EEG Auditory Stimuli – Amplitude Modulation Detection Amplitude Modulated Signal: Synthesized /a:/ with different depths 0% Modulation 50% Modulation 100% Modulation

Data Analysis: Example of time-frequency analysis (Gilley et al. 2014) Control Group LLP Group Gamma Theta Alpha Beta