Self-Consciousness and 'Split' Brains : The Minds' I

Could a single human being ever have multiple conscious minds? Some human beings do. The corpus callosum is a large pathway connecting the two hemispheres of the brain. In the second half of the twentieth century a number of people had this pathway cut through as a treatment for epilepsy. They became colloquially known as split-brain subjects. After the two hemispheres of the brain are cortically separated in this way, they begin to operate unusually independently of each other in the realm of thought, action, and conscious experience, almost as if each hemisphere now had a mind of its own. Philosophical discussion of the split-brain cases has overwhelmingly focused on questions of psychological identity in split-brain subjects, questions like: how many subjects of experience is a split-brain subject? How many intentional agents? How many persons? On the one hand, under experimental conditions, split-brain subjects often act in ways difficult to understand except in terms of each of them having two distinct streams or centers of consciousness. Split-brain subjects thus evoke the duality intuition: that a single split-brain human being is somehow composed of two thinking, experiencing, and acting things. On the other hand, a split-brain subject nonetheless seems like one of us, at the end of the day, rather than like two people sharing one body. In other words, split-brain subjects also evoke the unity intuition: that a split-brain subject is one person. Elizabeth Schechter argues that there are in fact two minds, subjects of experience, and intentional agents inside each split-brain human being: right and left. On the other hand, each split-brain subject is nonetheless one of us. The key to reconciling these two claims is to understand the ways in which each of us is transformed by self-consciousness. Cover 1 Self-Consciousness and “Split” Brains: The Minds’ I 4 Copyright 5 Dedication 6 Acknowledgments 8 Contents 10 List of Figures 14 1: The Unity Puzzle 18 1. The Dual Brain 18 2. The Split-Brain Surgeries 21 2.1. The first split-brain surgeries 22 2.2. The discovery of the split-brain phenomenon 22 2.3. The first split-brain experiments 25 2.4. Working with split-brain human beings 28 3. The Unity Debates 32 4. Outline of Book 35 5. On Paths Not Taken 36 2: Subjects of Experience and Subjective Perspectives 40 1. The Question of Split-Brain Consciousness 40 2. Conscious Unity and Disunity 42 2.1. Access unity and awareness unity 43 2.2. Delineating perspectives 44 3. The Positive Case for the 2-Perspectives Claim 45 3.1. The empirical basis of the 2-perspectives claim 46 3.2. The bihemispheric consciousness claim 48 3.3. Conscious unity as causal integration 49 3.4. Two qualitatively distinct perspectives 51 4. One Perspective Nonetheless 52 4.1. The 1-interhemispherically-switching-stream account 52 4.2. The conscious-unity-through-unified-agency account 56 4.3. The persisting-phenomenal-unity account 61 5. Subjects and Subjective Perspectives 63 3: Dual Intentional Agency 67 1. The Question of Split-Brain Agency 67 2. Intentional Agency 68 3. The Positive Case for the 2-Agents Claim 70 3.1. True agents versus zombie systems 70 3.2. Individual intentional agency 74 3.3. The autonomy condition on agency 76 3.4. Intentional autonomy 80 4. Dual Agency and Disunified Behavior 82 4.1. The objection from normal behavior 83 4.2. The objection from unified behavior 84 4.3. The objection from ordinary behavior 88 4.4. Dual agency in daily life 91 5. Agents and Anthropomorphism 95 4: How Many Minds? 97 1. Identities of Split-Brain Psychological Beings 97 2. Distinct Candidate Thinkers in the Split-Brain Case 98 3. The Case for the 2-Thinkers Claim 100 3.1. Interhemispheric independence 101 3.2. Thinkers as thinking systems 105 3.3. Misconceptions about the 2-thinkers claim 107 4. Indirect Interaction and Psychic Independence 112 4.1. Direct versus indirect interaction 112 4.2. The architecture of (a) mind 116 4.3. Mental duality versus the disunity of mind 119 5. Mental Duality versus the Partial Unity of Mind 122 5: Objection from Sub-Cortical Structures 124 1. Objection from Sub-Cortical Structures 124 2. Direct Interhemispheric Interaction in the Split-Brain Case 126 2.1. Unity of the ambient visual field 128 2.2. Transfer of semantic associations 129 2.3. Unified emotion and affect 130 2.4. Attention and other resources 132 2.5. Motor and motoric forms of integration 133 3. Non-Discrete Minds 135 4. The “Split” Brain and the Duality of Mind 137 4.1. The dual brain 138 4.2. Cross-cueing in split-brain subjects 145 4.3. Psychic autonomy 149 4.4. The agent of interaction 151 5. But Is It True? 153 6: Bodies and Being One 156 1. Unity and Necessity 156 2. Universal Plural Personhood 156 3. The Objection from Us 159 4. The Objection from I 163 5. S as the Object of Embodied Self-Awareness 164 5.1. Bodily self-awareness 165 5.2. Explicit self-consciousness versus implicit self-awareness 166 5.3. The implicit object of bodily self-awareness 169 6. The Self-Consciousness Objection to Any Reconciliation Account of the Split-Brain 170 7: Self and Other in the Split-Brain Subject 173 1. Self-Consciousness and Strict Self-Reference 173 2. I-Thoughts and I-Thinkers 174 2.1. RH Language and the 1-I-thinker claim 174 2.2. The 2-I-thinkers claim 176 2.3. R as I-thinker 176 3. Three Striking Features of Self-Consciousness in Split-Brain Subjects 179 3.1. Lack of mutual recognition 180 3.2. Common subjective identification 182 3.3. Lack of capacity for self-distinction 185 4. Capacity for Self-Distinction 187 4.1. Recognition and perception 188 4.2. Self-distinction 190 4.3. Distinguishing R from L 191 5. Subjective versus Objective Self-Reference 192 8: The Self-Consciousness Condition of Personhood 198 1. The Question of Split-Brain Personhood 198 2. Persons and the Interpersonal 200 2.1. Persons and personal capacities 201 2.2. The self-consciousness condition of personhood 202 2.3. Self-governance and social governance 205 2.4. Two distinctively interpersonal practices 206 2.5. Why social self-consciousness matters for personhood 209 3. R and L as One Interpersonal Agent 211 4. Objections to the Failure Argument 218 4.1. The relational fact objection 218 4.2. The overly strict objection 220 5. Objections to the Success Argument 221 5.1. Is S a thinker? 221 5.2. Self-knowledge and self-reference 225 5.3. Self-governance and psychic unity 225 9: Duality Myths 228 1. The Standard Explanation of the Split-Brain Sociological Phenomenon 228 2. Unity in Commonsense Psychology 229 3. Divided Minds and Duality Myths 230 4. Living Myths 232 5. R and L as They Are 235 Appendix 238 1. Visual Unity 238 2. Can Semantic Associations Transfer? 241 3. Unified Emotion and Affect 248 4. Unitary and Dual Attentional Systems 254 5. An at Some Level Unitary System for Motor Control 259 5.1. Competition for response control 260 5.2. Gating of bihemispheric motor information 261 5.3. Response coordination 268 Bibliography 276 Author Index 302 Subject Index 307 The largest fiber tract in the human brain is the corpus callosum, which connects the two cerebral hemispheres. A number of surgeries severing this structure were performed on adults in the United States in the second half of the twentieth century. After they are surgically separated from each other in this way, a “split-brain” subject’s hemispheres begin to operate unusually independently of each other in the realms of perception, cognition, and the control of action—almost as if each had a mind of its own. But can a mere hemisphere really see? Speak? Feel? Know what it has done? The split-brain cases raise questions of __psychological identity__: How many subjects of experience are there within a split-brain subject? How many persons? How many minds? Under experimental conditions, split-brain subjects often act as though they were animated by two distinct conscious beings, evoking the __duality intuition__. On the other hand, a split-brain subject seems like __one__ of us—not like __two__ of us sharing one body. Split-brain subjects thus also evoke the __unity intuition__.This book is devoted to reconciling these two apparently opposing intuitions. The key to doing so are facts about the way __self-consciousness__ operates in split-brain subjects. A split-brain subject is composed of two conscious psychological beings that fail to recognize each other’s existence and indeed cannot distinguish themselves from each other. Instead, each must first-personally identify with the split-brain subject as a whole, and in so doing, the two make themselves into one person. Elizabeth Schechter Explores The Implications Of The Experience Of People Who Have Had The Pathway Between The Two Hemispheres Of Their Brain Severed, And Argues That There Are In Fact Two Minds, Subjects Of Experience, And Intentional Agents Inside Each Split-brain Human Being: Right And Left. But Each Split-brain Subject Is Still One Of Us. Elizabeth Schechter.