Hemispheric Lateralization of Japanese Kanji and Kana: Evidence for Right Hemisphere Involvement in Semantic Processing of Kanji
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. HEMISPHERIC LATERALIZATION OF JAPANESE KANJIAND KANA: EVIDENCE FOR RIGHT HEMISPHERE INVOLVEMENT IN SEMANTIC PROCESSING OF KANJI by Chisato Aoki B. A. ,Doshisha University M. Ed. ,M. A. ,Northeastern University ABSTRACT OF DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Psychology in the Graduate School of Arts and Sciences of Northeastern University, January, 1990. The purpose of this research was to investigate whether the right hemisphere of the human brain is involved in linguistic (semantic) processing. Among right-handed persons, linguistic processing has been shown to be lateralized primarily in the left hemisphere (LH), while visual-spatial processing has been thought to be lateralized primarily in the right hemisphere (RH) (e. g. Gazzaniga, 1967; Kimura, 1961, 1966). Japanese orthography is a good tool with which to study this general issue because it has both ideographic characters, Kanji, and syllabic characters, Kana. Access to the Kanjilexicon may be achieved via visual-orthographic codes, without phonological mediation (Sait0, 1981), and so may involve the RH. However, access to the Kana lexicon requires prelexical phonological processing (Gory0, 1987; Sait0, 1981), presumably involving the LH. Thus the hypothesis of this thesis was that the RH would be better than the LH in processing the meaning of Kanji words, but the opposite pattern would hold for Kana words. Previous research has generally supported LH processing for Kana and RH for Kanji, although the pattern of results does depend on the task. For Kanji, earlier results are generally in line with the expectation of RH dominance for visually- sensitive tasks (Hatta, 1977; Sasanuma at a1. , 1977). Only when high-level semantic tasks are used, such as superordinate Gategorization and judgment of semantic congruence, does LH dominance occur with Kanji(Hatta, 1981; Hayashi & Hatta, 1982; Sasanuma at a1. , 1981). However, lateralization of the comprehension of word meaning, a lower-levelsemantic task, has not been previously tested. It is interesting to test RH involvement in word comprehension in normals, partly because clinical observations on Japanese partial split-brain and alexic patients suggest that the RH may be able to understand familiar and concrete Kanji words. The relative dominance of the RH and LH was tested in a series of tachistoscopic half-visual field experiments. A picture-word matching task was used to test the hypothesis. This task minimizes overt phonological processing, and does not require higher cognitive processes such as superordinate categorization. Two sets of experiments were conducted using this task. The first set (Expts. I-4) employed both Kanji and Kana. The pictures and words were matched for meaning (the "semantic" task). The reaction time (RT) for making the match was recorded. A cross-over interaction for the RTS between character type and visual field (i. e. , hemisphere) predicted by the hypothesis was obtained in a clear-cut fashion. This result extended previous work (Jones & Aoki, 1988). In the second set of Experiments'(6-8), only Kanji characters were used. These were tested not only in the "semantic" task but also in a "phonological" task in which the sound of the word was matched to the sound of the picture's name. Again, RTS showed an interaction between task and visual field, providing additional evidence to support the hypothesis that the RH is involved in comprehending Kanji words. This interaction, though clear in the first session, tended to wash out over subsequent . sessions. For both Kanji and Kana, the predicted interaction was strong only when both the picture and word were presented to the same visual field. When the picture was centered and only the word was lateralized, the interaction was reduced or disappeared. These aspects of the data may be consistent with hemispheric activation theory (Kmsbourne, 1973). Taken together, the results of this research indicate that in the picture-word matching task, using highly familiar and highly concrete words and lateralized presentations of both the picture and the character, Kana words are processed better in the LH, while Kanji words are processed better in the RH. This pattern of results supports the idea that LH function is necessary when prelexical phonology is required to access the lexicon, while the RH can comprehend the words when access to the lexicon is achieved by visual-orthographic codes, without phonological mediation. .. 11 Copyright 1990 Chisato Aoki NORTHEASTERN UNIVERSITY Graduate School of Arts and Sciences Dissertation Title: Hemispheric Lateralization of Japanese Kanji and Kana: Evidence for Right Hemisphere Involvement in Semantic Processing of Kanji Author: Chisato Aoki Department: Psychology Approval for Thesis Requirements of the Doctor of Philosophy Degree: I It fro . 11 , \ .//'.. , I. .{> I I I I^ ^/ ^,. a .^ , o ^^~ I ^ 9'0 Th sis Committee D to ;I, . IC^.* I~zf'-?O Head of Department Date NORTHEASTERN UNIVERSITY Graduate School of Arts and Sciences Dissertation Title: Hemispheric Lateralization of Japanese Kanji and Kana: Evidence for Right Hemisphere Involvement in Semantic Processing of Kanji Author: Chisato Aoki Department: Psychology Approved for Thesis Requirements of the Doctor of Philosophy Degree: ,. A^, ^' ?'o . I o I^^I^;,,, I, 00 I- f"- 90 ^^. I 8 ?'O Th sis Committee te IC I-^-^O Head of partment Date Graduate School Notified of Acceptance: I A1"' I^ 12 6z. -/,,- ,) Signed te Copy Deposited in Library: Signed Date . 111 ACKNOWLEDGEMENTS This dissertation could not have been completed without the contributions and help of many people. I would like to express my appreciation to my dissertation adviser, Dr. Adam Reeves, who kindly allowed me to work independently, and gave me his intellectual as well as technical support whenever I needed. I am especially indebted to Dr. Adam Reeves for his tremendous patience and effort to read the manuscript many times and improve my writing. I also would like to thank my former adviser, Dr. Martin Block, for his guidance and support thoughout my graduate career. I am grateful to the other members of my committee, Drs. Harold Goodglass, Nancy Hildebrandt, and Nancy Soja, who gave me critical comments and constant encouragement throughout my work. I would like to thank anthe faculty members in the Department of Psychology, who gave me an outstanding opportunity to learn about various fields of psychology in the U. S. I especially would like to express my gratitude to Dr. John Armington, who advised me to stay in this program. Without his advice, I could not have completed my Ph. D. in the U. S. I also want to thank my fellow graduate students in the Vision Lab and Language & Cognition Group, especially Marc Bearse, who acted as sounding boards for my ideas. My special thanks go to BTOhmsek Yen-ura, my wonderful assistant and very good friend. He helped me with finding subjects, running experiments, inputing data and correcting the manuscript of this thesis. More importantly, he cheered me up with his unique jokes whenever I was down, and encouraged me throughout my work. Without his help, I could not have completed my dissertation. IV A special note of appreciation is extended to all of my Japanese subjects, who kindly participated in my experiments. I would especially like to thank Mr. Sakamaki, the head of Showa Women's Institute in Boston, who provided me with Japanese students for my research. Finally, I would like to thank my parents, thousands of miles away, who encouraged me and supported me throughout my graduate career. Their faith and confidence in me led me to the end of this long road. HEMISPHERIC LATERALIZATION OF JAPANESE KANJIAND KANA: EVIDENCE FOR RIGHT HEMISPHERE INVOLVEMENT IN SEMANTIC PROCESSING OF KANJI A Dissertation presented by Chisato Aoki to The Department of Psychology In partial fulfillment of the requirements for the degree of Doctor of Philosophy in the field of Psychology Northeastern University Boston, Massachusetts January, 1990 . , V TABLE OF CONTENTS Acknowledgements ................................................................................................... in Chapter I : Introduction. ............................................................................................. I Introduction ...................................................................................................... I Background ....................................................................................................... 4 I. The Nature of Kanji and Kana. ................................................................. 4 2. Cognitive Psychological Study .................................................................... 7 3. Clinical Observations ...............................................................................----8 4. Tachistoscopic Visual Half-Field Studies ................................................ 12 5. Semantic Processingg in the Right Hemisphere ...................................... 15 Hypothesis ....................................................................................................... I 7 Chapter 2: Semantic Task with Kanji and Kana. .................................................. 18 Introduction ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,..................................................... I , q Experiment I: a short presentation of a lateralized picture. ....................... 20 Experiment 2: a long presentation of a lateralized picture.