Sublexical, lexical and phonological short-term memory processes: Evaluating models of speech perception and short-term memory

Sublexical, lexical and phonological short-term memory processes: Evaluating models of speech perception and short-term memory by Heather Raye Dial The current research examined the processes involved in speech perception and the relation of speech perception to phonological short-term memory (pSTM). Contrary to traditional models which assume that sublexical processing necessarily precedes lexical processing (e.g., McClelland & Elman, 1986; Norris, 1994), several studies have demonstrated that patients may perform better on lexical than sublexical speech perception tasks (e.g., Miceli, Gainotti, Caltagirone, & Masullo, 1980). These findings have led to proposals of separate sublexical and lexical routes in speech perception (dual route models; e.g., Hickok & Poeppel, 2000). However, studies demonstrating these dissociations did not closely match the phonological similarity of targets and distractors or task demands between sublexical and lexical tasks. Experiment 1, which rectified these design problems, demonstrated a close correspondence between sublexical and lexical processing across several speech discrimination tasks for brain damaged patients and supported obligatory sublexical processing models of speech perception. Experiment 2 sought to provide converging evidence by tracking patients’ eye movements while they performed sublexical and lexical identification tasks. As in Experiment 1, there was evidence a) of a close correspondence between sublexical and lexical processing and b) for obligatory sublexical processing. However, there were some dependent measures that failed to support the obligatory sublexical processing framework. Dual route models additionally claim that pSTM depends on the brain regions involved in perception, including a sensory-motor interface region involved in rehearsal (e.g., Hickock & Poeppel, 2000). In contrast, traditional models of pSTM assume a phonological maintenance buffer separate from perceptual processes (Martin & Breedin, 1992). In Experiment 3 we found behavioral and structural neuroimaging (lesion-symptom mapping) support for the buffer approach, though no significant results were found in attempts to localize sublexical and lexical processing. Acknowledgements First, I would like to thank my advisor and mentor of the past six years, Dr. Randi Martin. I owe much of what I have accomplished to her guidance and wisdom, criticisms and encouragement. I am a better person and scientist for having worked under her. I would also like to thank my other committee members, Dr. Caleb Kemere and Dr. Simon Fischer-Baum. I am especially grateful to Simon for having gone above and beyond, sitting with me to flesh out ideas, work through difficult research papers, and provide valuable career advice. For statistical guidance, I would like to thank Dr. David Lane. I am also indebted to the current and former members of the Brain and Language Lab: Corinne Allen-Pettigrew, Cris Hamilton, Azli Hassan, Yi Guo, Yingying Tan, Hao Yan, Qiuhai Yue, and Curtiss Chapman. I am so glad to have gotten to know each of these people and to have had the opportunity to learn from their experiences. Last of the Rice community, but certainly not least, I owe a great deal of thanks to Lanita Martin. Lanita has become more like family and has been there for me in my times of deepest need. For this she will forever hold a place in my heart. Outside of Rice, there are many people who deserve my thanks. First, I need to thank Ben Gott, my partner throughout my graduate studies, without whom I might have given up a long time ago. I’d also like to thank my caring family, Erin Dial-LaFleur, Jaye Dial, Sherri Dial, Tina Kelley, Joan Jarrell, Lesley Howell and Janice Marye, for always, always, providing me unconditional love and support. Finally, I’d like to thank two people I lost along the way, my father, Darren Dial, and grandmother, Geraldine DiBiase-these two people are more important to me than almost anything else in this world. This entire work is dedicated to them in memory of all they taught me. CONTENTS Acknowledgements . iv