Auditory and speech processing in Specific Language Impairment (SLI) and dyslexia Outi Tuomainen Thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy University College London June 2009 I, Outi Tuomainen , confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. 2 ABSTRACT This thesis investigates auditory and speech processing in Specific Language Impairment (SLI) and dyslexia. One influential theory of SLI and dyslexia postulates that both SLI and dyslexia stem from similar underlying sensory deficit that impacts speech perception and phonological development leading to oral language and literacy deficits. Previous studies, however, have shown that these underlying sensory deficits exist in only a subgroup of language impaired individuals, and the exact nature of these deficits is still largely unknown. The present thesis investigates three aspects of auditory-phonetic interface: 1) The weighting of acoustic cues to phonetic voicing contrast 2) the preattentive and attentive discrimination of speech and non-linguistic stimuli and 3) the formation of auditory memory traces for speech and non-linguistic stimuli in young adults with SLI and dyslexia. This thesis focuses on looking at both individial and group-level data of auditory and speech processing and their relationship with higher-level language measures. The groups of people with SLI and dyslexia who participated were aged between 14 and 25 and their performance was compared to a group of controls matched on chronological age, IQ, gender and handedness. Investigations revealed a complex pattern of behaviour. The results showed that individuals with SLI or dyslexia are not poor at discriminating sounds (whether speech or non-speech). However, in all experiments, there was more variation and more outliers in the SLI group indicating that auditory deficits may occur in a small subgroup of the SLI population. Moreover, investigations of the exact nature of the input-processing deficit revealed that some individuals with SLI have less categorical representations for speech sounds and that they weight the acoustic cues to phonemic identity differently from controls and dyslexics. 3 ACKNOWLEDGEMENTS My sincere thanks are to all the people who participated in this study. I also wish to thank their families and guardians who gave their permission and their time for this study. I wish to express my gratitude to my loyal pilot subject, JT, who took part in all the experiments (over and over again), their pilot versions and gave me a hand during the weekend testing sessions. I thank a team of people who supervised my work and/or gave their comments on my work (in alphabetical order): Dr. Chris Donlan, Prof. Karl Friston, Prof. Valerie Hazan, Prof. Heather van der Lely and Dr. Anna Shestakova. Any errors, however, remain mine. Furthermore, I wish to address a particular thank to all staff and students at the (former) departments of Human Communication Science and Phonetics and Linguistics as well as at the Wellcome Trust Centre for Neuroimaging -and especially to Dr. Flavia Adani, Yin-Juei Chang, Dr. Mike Coleman, Dr. Nichola Gallon, Kristjan Kalm, Dr. Elena Kushnerenko, Dr. Alex Leff, Dr. Chloe Marshall, Dr. Yasuyo Mingawa-Kawai, Steve Newton, Angela Pozzuto, Tom Schofield, Saleh al-Shaalan, Dr. Marisa Silveira and Athina Skordi. Finally, I would like to thank Prof. Heikki Hämäläinen at the Centre for Cognitive Neuroscience at University of Turku (Finland) for kindly providing me a quiet office space for the write-up of this thesis along with all my friends at the CCN. 4 TABLE OF CONTENTS 1. Thesis outline ...............................................................................................................11 2. Specific Language Impairment ....................................................................................11 2.1 Introduction............................................................................................................11 2.2 Characteristics of SLI.............................................................................................13 2.2.1 Syntax..........................................................................................................13 2.2.2 Morphology.................................................................................................14 2.2.3 Phonology ...................................................................................................16 2.2.4 Auditory processing ....................................................................................17 2.3 Sub-grouping SLI...............................................................................................25 2.4 Causes of SLI .....................................................................................................27 2.4.1 The biological causes of SLI.......................................................................28 2.4.2 The cognitive causes of SLI........................................................................29 2.4.2.1 The domain-specific account ...................................................................29 2.4.2.2 The domain-general account....................................................................32 2.6 Summary ............................................................................................................37 3. Developmental dyslexia...............................................................................................38 3.1 Introduction........................................................................................................38 3.2 Understanding dyslexia......................................................................................39 3.2.1 Biological level ...........................................................................................39 3.2.2 Cognitive level ............................................................................................41 3.2.2.1 Magnocellular theory ...............................................................................42 3.2.2.2 Phonological theory .................................................................................47 3.2.3 Behavioural level ........................................................................................50 3.3 SLI and dyslexia: the same disorder? ................................................................52 3.5 Summary ............................................................................................................56 4. Speech Perception: From Phonetics to Phonology ......................................................57 4.1 Introduction........................................................................................................57 4.2 The problem of speech perception .....................................................................57 4.2.1 Auditory theories of speech perception.......................................................60 5 4.3 Integrating multiple cues: trading relations and acoustic cue weight ................62 4.4 Development of speech perception ....................................................................67 4.4.1 Categorical perception of sounds................................................................67 4.4.2 Development of phonological categories....................................................70 4.5 Speech sound processing in the auditory cortex ................................................73 4.5.1 Mismatch negativity (MMN) as an index of auditory sensory memory.....75 4.6 Summary ............................................................................................................81 5. Aims and structure of the thesis...................................................................................82 5.1 Participant selection in the current thesis...........................................................83 5.2 Stimulus selection in the current thesis..............................................................89 6. Cue weighting in Specific Language Impairment (SLI) and dyslexia.........................91 6.1 Introduction........................................................................................................91 6.2 Method ...............................................................................................................93 6.2.1 Participants..................................................................................................93 6.2.2 Stimuli.........................................................................................................95 6.2.3 Procedure.....................................................................................................97 6.3 Results................................................................................................................98 6.3.1 Correlations...............................................................................................101 6.3.2 Individual data and within-category variation ..........................................102 6.4 Discussion and conclusion ...............................................................................107 7. Electrophysiological investigation of auditory processing in SLI and dyslexia........110 7.1 Introduction......................................................................................................110 7.1.1 Chapter outline..........................................................................................110