Bangor University DOCTOR OF PHILOSOPHY Cerebral asymmetries: handedness and the right hemisphere Karlsson, Emma Award date: 2019 Awarding institution: Bangor University Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 03. Oct. 2021 Cerebral asymmetries: Handedness and the right hemisphere Emma M. Karlsson Thesis submitted to the School of Psychology, Bangor University, in partial fulfillment of the requirements for the degree of Doctor of Philosophy School of Psychology Bangor University May 2019 Acknowledgments I would like to thank the examiners for their time and effort in reading and assessing this thesis. I would like to express my gratitude to my supervisor, Dr David Carey. You have made this project an absolute joy, and this experience would definitely not have been the same without your (unfiltered) encouragement, enthusiasm, and support. Thank you for giving me the opportunity to carry on with this fascinating line of research. A special thanks goes to my second supervisor Dr Patricia Bestelmeyer who has proved imaging and auditory expertise for this project. Furthermore, thanks to Dr Paul Mullins for all the imaging support, and to Andrew Fischer for all the help during MRI scanning sessions. I would also like to say a special thanks to David McKiernan, James Morgan, Elfyn Roberts, and Llewelyn Morris for all the technical support and expertise provided throughout this project. I am especially grateful to David McKiernan who always found time to help, and who’s innovative and magic-like skills saved this project from various disastrous outcomes on more than one occasion. This research would not have been possible without the dedication of the participants who took part; thank you for your time and effort to help create this piece of work. Lynn, Scott, and Noelle – thank you for your encouragement and for and introducing me to the world of academia. Lastly, I would like to extend my gratitude to my family and friends who have supported me throughout these past few years – both old friends and new ones I have been lucky enough to meet throughout this journey. - Tack från hela mitt hjärta i Summary There are well-known, but poorly understood, links between left cerebral language dominance and hand preference. Approximately 95% of right-handers and 70% of non-right- handers have language lateralised to the left hemisphere. In contrast, virtually nothing is known about handedness and cerebral dominance for a number of different specialisations linked with the right cerebral hemisphere. This thesis examines several of these asymmetries, including face, emotional, attentional, and body processing, in right-handed and non-right- handed groups using both behavioural and neuroimaging techniques. The main aims of these investigations were to quantify the frequencies of these biases, and to examine possible links between each of these asymmetries and speech/language, to see if they ‘anti-localise’ in the two hemispheres in a complementary fashion. To do this, a large pool of language ‘atypicals’ (individuals with right hemisphere dominance for language) were identified for inclusion in the neuroimaging experiments. An important foundation of this work advocates the use of proportional and individual level analyses, rather than the usual exclusive reliance on typical inferential statistics that focus on measures of central tendency. First, a large-scale battery of perceptual tests, which included measures of language, emotional, attentional, and face-related asymmetry, was administered to a large sample of right-handers and non-right-handers (Chapter 2). These efforts were coupled with a large- scale functional neuroimaging series, quantifying cerebral asymmetries for emotional prosody, emotional vocalisations, bodies, neutral and emotional faces, as well as for language (Chapter 3). The final empirical chapter attempts to predict the neuroimaging asymmetry groups from behavioural measures of asymmetry (Chapter 4). The results from this thesis confirms the links of the ‘target specialisations’ to the right hemisphere for the majority of individuals. Intriguingly, it also suggests that there are moderating effects of handedness, with non-right-handers having a more varied laterality profile whilst right-handed participants were largely complementary for all functions measured. The atypically lateralised individuals had the most varied asymmetry profiles, in spite of remarkably similar asymmetry for language with the right-handed and non-right-handed language typical groups. These results are discussed in terms of models of hemispheric specialisation, the use of perceptual tests to aid in the identification of individuals with rare laterality patterns, and future studies important for a full appreciation of cerebral dominance and human handedness. ii Table of contents Chapter 1 - General introduction.......................................................................... 1 1.1 The relationship between handedness and functional cerebral asymmetries for language…...................................................................................................... 1 1.2 Asymmetries and the right hemisphere: neuropsychological evidence.......... 5 1.3 Behavioural asymmetries: perceptual asymmetries relating to cerebral asymmetries......................................................................................................... 9 1.4 fMRI as a measure of functional asymmetries............................................... 14 1.5 Complementarity of hemispheric specialisations........................................... 21 1.6 Outstanding questions and thesis overview................................................... 24 Chapter 2 - Perceptual asymmetries in right-handers and non-right- handers…………..................................................................................................... 26 2.1 Introduction..................................................................................................... 26 2.2 Methods.......................................................................................................... 34 2.3 Results........................................................................................................... 50 2.4 Discussion...................................................................................................... 59 Chapter 3 - Functional asymmetries in right-handers and non-right- handers................................................................................................................... 64 3.1 Introduction..................................................................................................... 64 3.2 Methods.......................................................................................................... 77 3.3 Results........................................................................................................... 87 3.4 Discussion...................................................................................................... 117 Chapter 4 - Behavioural predictors of functional cerebral asymmetries......... 124 4.1 Introduction..................................................................................................... 124 4.2 Methods.......................................................................................................... 131 4.3 Results........................................................................................................... 133 4.4 Discussion...................................................................................................... 139 Chapter 5 - General discussion............................................................................ 142 5.1 Chapter 2 – Perceptual asymmetries in right-handers and non-right- handers................................................................................................................ 142 iii 5.2 Chapter 3 - Functional asymmetries in right-handers and non-right-handers 146 5.3 Chapter 4 - Behavioural predictors of functional cerebral asymmetries......... 148 5.4 Chapter 3 - Remaining themes and questions .............................................. 149 5.5 Concluding remarks....................................................................................... 155 References............................................................................................................. 156 Appendices............................................................................................................ 205 Appendix A.............................................................................................................. 205 Appendix B.............................................................................................................